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* ABSTRACT
* I. INTRODUCTION
* II. FUNDAMENTALS OF THE HER
* III. BRIEF OVERVIEW OF THE HER ELECTROCATALYSTS BASED ON NON-PT NMNs
* IV. CONSTRUCTING ROBUST NON-PT NOBLE METAL-BASED ELECTROCATALYSTS TOWARD THE
HER
* V. NEW TRENDS IN THE ELECTROCATALYTIC HER
* VI. CONCLUSIONS AND OUTLOOK
* ACKNOWLEDGMENTS
* DATA AVAILABILITY
* REFERENCES
ROBUST NON-PT NOBLE METAL-BASED NANOMATERIALS FOR ELECTROCATALYTIC HYDROGEN
GENERATION
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* Volume 7, Issue 4 >
* 10.1063/5.0021578
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Free Submitted: 20 July 2020 Accepted: 24 September 2020 Published Online: 16
October 2020
* ROBUST NON-PT NOBLE METAL-BASED NANOMATERIALS FOR ELECTROCATALYTIC HYDROGEN
GENERATION
*
Applied Physics Reviews 7, 041304 (2020); https://doi.org/10.1063/5.0021578
Jie Yu1, Yawen Dai1, Qijiao He1, Chun Cheng1, Zongping Shao2,3,a), and Meng
Ni1,4,a)
more...View Affiliations
* 1Department of Building and Real Estate, The Hong Kong Polytechnic
University, Hung Hom, Kowloon, Hong Kong 999077, China
* 2State Key Laboratory of Materials-Oriented Chemical Engineering, College of
Chemical Engineering, Nanjing Tech University, No. 5, Xin Mofan Road, Nanjing
210009, People's Republic of China
* 3Department of Chemical Engineering, Curtin University, Perth, Western
Australia 6845, Australia
* 4Environmental Energy Research Group, Research Institute for Sustainable
Urban Development (RISUD), The Hong Kong Polytechnic University, Hung Hom,
Kowloon, Hong Kong 999077, China
* a)Authors to whom correspondence should be addressed: shaozp@njtech.edu.cn
and meng.ni@polyu.edu.hk
View Contributors
* Jie Yu
* Yawen Dai
* Qijiao He
* Chun Cheng
* Zongping Shao
* Meng Ni
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ABSTRACT
Currently, the electrocatalytic hydrogen evolution reaction (HER) has been a key
point of focus for developing sustainable hydrogen economy, but it is hampered
by sluggish reaction kinetics. Despite the fact that various non-noble
metal-based materials as electrocatalysts toward the HER are gaining
considerable attention, noble metal-based nanomaterials (NMNs) for catalyzing
the HER still have advantageous features, i.e., wide pH applicability, high
intrinsic activity, and good stability. Considering a high chemical similarity
to HER-benchmark Pt metals, various non-Pt NMNs with high atom utilization,
super efficiency, and durability for HER catalysis are engineered through
various structural/electronic tailoring strategies, which has become a
significant trend in this research field. Herein, a panoramic review about
recent representative efforts and progress in the design of non-Pt NMNs is
presented. It first introduces the HER fundamentals and then generally describes
the structural and electronic characteristics of non-Pt noble metals matching
the HER. Followed on, different tuning strategies for fabricating effective
non-Pt NMN catalysts, including composition optimizing by constructing alloys or
novel compounds, morphological tuning via decreasing the particle size or
designing unique nanostructures, and hybrid engineering as well as crystalline
structure/facet controlling, are systemically summarized, with a special focus
on the underlying structure–activity relationship for different catalysts. The
features of pH universality and bifunctionality for these non-Pt NMN catalysts
are also highlighted. At the end, existing challenges and future perspectives
awaiting this emerging research field are discussed.
I. INTRODUCTION
Section:
ChooseTop of pageABSTRACTI. INTRODUCTION <<II. FUNDAMENTALS OF THE H...III.
BRIEF OVERVIEW OF TH...IV. CONSTRUCTING ROBUST N...V. NEW TRENDS IN THE
ELEC...VI. CONCLUSIONS AND OUTLO...Choose
Energy plays a crucial role in our daily life, which also drives the rapid
advancement of our society. As we all know, ever since the industrial
revolution, modern society has relied more and more heavily on exhaustible
fossil fuels.1,21. Y. Zhao, W. Gao, S. Li, G. R. Williams, A. H. Mahadi, and D.
Ma, “ Solar-versus thermal-driven catalysis for energy conversion,” Joule 3(4),
920–937 (2019). https://doi.org/10.1016/j.joule.2019.03.0032. S. Chu and A.
Majumdar, “ Opportunities and challenges for a sustainable energy future,”
Nature 488(7411), 294–303 (2012). https://doi.org/10.1038/nature11475 It is
roughly estimated that over 79.5% consumption of energy in the whole world comes
from traditional fossil fuels.33. REN21, see
http://www.ren21.net/about-ren21/about-us/ for “ Renewables 2018 Global Status
Report, 2018.” However, fossil fuels are non-renewable and emit a lot of
pollutants and greenhouse gas during their utilization. Actually, the excessive
use of fossil fuels based on low-efficiency combustion technology has caused
many negative effects on the earth's environment, such as the formation of haze,
acid rain, and extreme climate.33. REN21, see
http://www.ren21.net/about-ren21/about-us/ for “ Renewables 2018 Global Status
Report, 2018.” It is well accepted that in order to realize a sustainable
development of our society, clean and sustainable energy systems should be
adopted. Wind, tidal, and solar energies are renewable, abundant, and
carbon-neutral, which are ideal energy resources to replace traditional fossil
fuels for the future.44. C. G. Morales-Guio, S. D. Tilley, H. Vrubel, M.
Grätzel, and X. Hu, “ Hydrogen evolution from a copper (I) oxide photocathode
coated with an amorphous molybdenum sulphide catalyst,” Nat. Commun. 5, 3059
(2014). https://doi.org/10.1038/ncomms4059 However, these renewable energies are
intermittent and site-specific, which hamper their wide application.55. R.
Banos, F. Manzano-Agugliaro, F. G. Montoya, C. Gil, A. Alcayde, and J. Gomez, “
Optimization methods applied to renewable and sustainable energy: A review,”
Renewable Sustainable Energy Rev. 15(4), 1753–1766 (2011).
https://doi.org/10.1016/j.rser.2010.12.008 To reliably utilize renewable
energies, effective energy storage is essential, such as electrochemical energy
storage by batteries, pumped hydro-energy storage, flywheel energy storage,
compressed gas energy storage, etc. However, large scale electrical energy
storage using batteries is costly as large-scale batteries are needed. The
pumped hydro and compressed gas storages are inexpensive, but are site-specific.
Flywheel energy storage suffers from significant self-discharge and is not
suitable for long-term energy storage. Alternatively, the excess renewable power
can be stored as chemical energy by driving an electrolysis cell for generating
hydrogen (H2) gas, which can be converted back to electricity using a fuel cell
when the renewable power is insufficient. As H2 can be stored, transported, and
converted without much difficulty, as depicted in Fig. 1, it is considered as a
promising energy carrier for energy storage.66. J. Wang, F. Xu, H. Jin, Y. Chen,
and Y. Wang, “ Non-noble metal-based carbon composites in hydrogen evolution
reaction: Fundamentals to applications,” Adv. Mater. 29(14), 1605838 (2017).
https://doi.org/10.1002/adma.201605838 H2 has the largest gravimetric energy
density among various available fuels and is carbon-free.77. S. Yuan, S.-Y.
Pang, and J. Hao, “ 2D transition metal dichalcogenides, carbides, nitrides, and
their applications in supercapacitors and electrocatalytic hydrogen evolution
reaction,” Appl. Phys. Rev. 7, 021304 (2020). https://doi.org/10.1063/5.0005141
Moreover, hydrogen production based on water electrolysis is also regarded as a
highly clean and sustainable approach due to water as the sole starting raw
material and high-purity hydrogen as the product.
FIG. 1. An overall ideal route toward distributed power generation based on
stable and sustainable hydrogen renewable energy supply.
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* High-resolution
In such a typical electrochemical water-splitting system, two half-cell
reactions, i.e., oxygen evolution reaction (OER) at the anode and hydrogen
evolution reaction (HER) at the cathode, are involved. The occurrence of these
two reactions requires additional energy input to overcome the reaction energy
barrier, known as a dynamic overpotential.8,98. S. Anantharaj, S. R. Ede, K.
Karthick, S. S. Sankar, K. Sangeetha, P. E. Karthik, and S. Kundu, “ Precision
and correctness in the evaluation of electrocatalytic water splitting:
Revisiting activity parameters with a critical assessment,” Energy Environ. Sci.
11(4), 744–771 (2018). https://doi.org/10.1039/C7EE03457A9. J. Yu, R. Ran, Y.
Zhong, W. Zhou, M. Ni, and Z. Shao, “ Advances in porous perovskites: Synthesis
and electrocatalytic performance in fuel cells and metal-air batteries,” Energy
Environ. Mater. 3(2), 121–145 (2020). https://doi.org/10.1002/eem2.12064 Certain
catalysts are needed to minimize this overpotential and hence save the energy.
As to the HER, considerable research studies have been conducted to develop
various efficient electrocatalysts in recent years, including noble-metal
nanomaterials (NMNs), transition metals (TMs), their corresponding oxides
(TMOs), phosphides (TMPs), chalcogenides (TMDs), nitrides (TMNs), and carbides
(TMCs), as well as metal-free composites.1010. J. Zhu, L. Hu, P. Zhao, L. Y. S.
Lee, and K.-Y. Wong, “ Recent advances in electrocatalytic hydrogen evolution
using nanoparticles,” Chem. Rev. 120(2), 851–918 (2020).
https://doi.org/10.1021/acs.chemrev.9b00248 Compared to noble metals (NMs),
these transition metal-based or metal-free materials feature earth abundance,
low cost, and certain electrocatalytic performances. However, they also show
some inherent drawbacks, mainly of poor conductivity, limited pH applicability,
low intrinsic activity, and weak durability, which can hinder their practical
applications.11–1311. Y. Zhao, J. Bai, X.-R. Wu, P. Chen, P.-J. Jin, H.-C. Yao,
and Y. Chen, “ Atomically ultrathin RhCo alloy nanosheet aggregates for
efficient water electrolysis in broad pH range,” J. Mater. Chem. A 7(27),
16437–16446 (2019). https://doi.org/10.1039/C9TA05334D12. J. Yu, Q. He, G. Yang,
W. Zhou, Z. Shao, and M. Ni, “ Recent advances and prospective in
ruthenium-based materials for electrochemical water splitting,” ACS Catal.
9(11), 9973–10011 (2019). https://doi.org/10.1021/acscatal.9b0245713. C. Li and
J.-B. Baek, “ Recent advances in noble metal (Pt, Ru, and Ir)-based
electrocatalysts for efficient hydrogen evolution reaction,” ACS Omega 5(1),
31–40 (2020). https://doi.org/10.1021/acsomega.9b03550 At least, in the near
future, it is still a big challenge for the widespread application of these
noble metal-free electrocatalysts in large scale water electrolysis for hydrogen
production. Consequently, the noble-metal nanomaterials, with super activity and
robust stability in a wide range of pH, are still the most attractive
electrocatalysts for the HER to ensure an energy-efficient water-splitting
procedure.
As always, platinum (Pt) is considered as the benchmark electrocatalyst for the
HER in all ranges of pH, which expresses nearly zero overpotential, low Tafel
slope, and superior long-term durability. With regard to other platinum-group
noble metals, like Ru, Rh, Pd, and Ir, they possess a high similarity to Pt
metal in chemical inertness and thus theoretically are also promising HER
catalysts.13,1413. C. Li and J.-B. Baek, “ Recent advances in noble metal (Pt,
Ru, and Ir)-based electrocatalysts for efficient hydrogen evolution reaction,”
ACS Omega 5(1), 31–40 (2020). https://doi.org/10.1021/acsomega.9b0355014. Z. W.
Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov, and T. F.
Jaramillo, “ Combining theory and experiment in electrocatalysis: Insights into
materials design,” Science 355(6321), eaad4998 (2017).
https://doi.org/10.1126/science.aad4998 More importantly, the HER activity of Pt
in basic media is approximately two or three orders of magnitude inferior to
that in acidic media due to slow water-dissociation kinetics, while there is
only one order of magnitude performance variation between basic and acidic
solutions for other noble metals, i.e., Ru or Rh.1515. N. Zhang, Q. Shao, Y. Pi,
J. Guo, and X. Huang, “ Solvent-mediated shape tuning of well-defined rhodium
nanocrystals for efficient electrochemical water splitting,” Chem. Mater.
29(11), 5009–5015 (2017). https://doi.org/10.1021/acs.chemmater.7b01588
Accordingly, much attention has been paid to these non-Pt noble metal
electrocatalysts with great success in the last years. Furthermore, taking the
scarce reserve for noble metals into consideration concurrently, researchers
mainly employed various tuning strategies to rationally design non-Pt noble
metal-based nanomaterials (NMNs) with high utilization amounts of noble metals,
well-exposed active sites, enhanced intrinsic activity of each active center,
and excellent electronic conductivity in the past 5 years.16–2016. P. Jiang, H.
Huang, J. Diao, S. Gong, S. Chen, J. Lu, C. Wang, Z. Sun, G. Xia, and K. Yang, “
Improving electrocatalytic activity of iridium for hydrogen evolution at high
current densities above 1000 mA cm−2,” Appl. Catal. B 258(5), 117965 (2019).
https://doi.org/10.1016/j.apcatb.2019.11796517. J. Feng, F. Lv, W. Zhang, P. Li,
K. Wang, C. Yang, B. Wang, Y. Yang, J. Zhou, and F. Lin, “ Iridium-based
multimetallic porous hollow nanocrystals for efficient overall-water-splitting
catalysis,” Adv. Mater. 29(47), 1703798 (2017).
https://doi.org/10.1002/adma.20170379818. B. Zhang, C. Zhu, Z. Wu, E. Stavitski,
Y. H. Lui, T.-H. Kim, H. Liu, L. Huang, X. Luan, and L. Zhou, “ Integrating Rh
species with NiFe-layered double hydroxide for overall water splitting,” Nano
Lett. 20(1), 136–144 (2020). https://doi.org/10.1021/acs.nanolett.9b0346019. J.
Ge, P. Wei, G. Wu, Y. Liu, T. Yuan, Z. Li, Y. Qu, Y. Wu, H. Li, and Z. Zhuang, “
Ultrathin palladium nanomesh for electrocatalysis,” Angew. Chem., Int. Ed.
130(13), 3493–3496 (2018). https://doi.org/10.1002/ange.20180055220. J. Wang, Z.
Wei, S. Mao, H. Li, and Y. Wang, “ Highly uniform Ru nanoparticles over N-doped
carbon: pH and temperature-universal hydrogen release from water reduction,”
Energy Environ. Sci. 11(4), 800–806 (2018). https://doi.org/10.1039/C7EE03345A
These tuning methods, as summarized in Fig. 2, include optimizing element
composition by forming alloys or constructing novel compounds, downsizing the
particle dimension to a few nanometers or developing a unique morphology, and
building up hybrids with another inexpensive but useful component as well as
controlling crystalline structures or exposed facets. Following these
substantial achievements, here we provide a comprehensive and timely summary
about the recent advances in the design and synthesis of non-Pt NMNs (Ru, Rh,
Pd, Ag, Ir, and Au) for HER electrocatalysis, which starts with a brief
discussion on the general catalytic mechanisms of the HER and the proposed
“volcano”-type plots toward electrocatalytic activity. Then, we also simply
review several structural and electronic characteristics matching the HER for
these non-Pt noble metals. Subsequently, fruitful achievements of non-Pt NMN
catalysts in the past 5 years are introduced with a key emphasis on the
state-of-the-art engineering strategies, as mentioned above, for tailoring the
catalytic activity. Meanwhile, light will be shed on the underlying
structure–activity relationship and mechanism. Additionally, a particular focus
on these non-Pt NMN catalysts with pH universality and bifunctionality is given
in the fourth section. Lastly, we propose the major challenges for the non-Pt
NMN HER catalysts and offer perspectives on future research work.
FIG. 2. Illustration of the tuning strategies for rationally designing non-Pt
NMNs toward an efficient HER.
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II. FUNDAMENTALS OF THE HER
Section:
ChooseTop of pageABSTRACTI. INTRODUCTIONII. FUNDAMENTALS OF THE H... <<III.
BRIEF OVERVIEW OF TH...IV. CONSTRUCTING ROBUST N...V. NEW TRENDS IN THE
ELEC...VI. CONCLUSIONS AND OUTLO...Choose
A. General reaction mechanisms
The HER undergoes a two-step two-electron reduction process under any pH
condition, which has been suggested as three possible principal reactions.2121.
Y. Shi and B. Zhang, “ Recent advances in transition metal phosphide
nanomaterials: Synthesis and applications in hydrogen evolution reaction,” Chem.
Soc. Rev. 45(6), 1529–1541 (2016). https://doi.org/10.1039/C5CS00434A In the
first step, i.e., the electrochemical adsorption/reduction process (the Volmer
reaction), a proton adsorbed on the electrode material surface couples with an
electron to form an adsorbed hydrogen intermediate (Hads) [Eqs. (1) and (2)].
With different electrolytes, the proton exists in different forms. Hydrogen ions
(H+) work as the proton source in acid, while the protons stem from the cleaving
of H–O–H bonds in basic solution.
Volmer reaction:
H++ e−→ Hads (in acidic media),H++ e−→ Hads (in acidic media),
(1)
H2O + e−→ Hads+ OH− (in neutral or basic media).H2O + e−→ Hads+ OH− (in neutral or basic media).
(2)
Subsequently, the second step shows two different pathways for the production of
H2 molecules. One is known as the Heyrovsky reaction, which occurs at low Hads
coverage. In this way, an as-formed Hads species combines with another proton
and a new electron to evolve H2 [Eqs. (3) and (4)].
Heyrovsky reaction:
H++ Hads+ e−→ H2 (in acidic media),H++ Hads+ e−→ H2 (in acidic media),
(3)
H2O + Hads+ e−→ H2+ OH− (in neutral or basic media).H2O + Hads+ e−→ H2+ OH− (in neutral or basic media).
(4)
However, when the coverage of Hads is relatively high, two adjacent Hads species
prefer to directly react with each other to give a H2 molecule, which is named
as the Tafel reaction [Eq. (5)].
Tafel reaction:
Hads+ Hads→ H2 (in pH−universal media).Hads+ Hads→ H2 (in pH−universal media).
(5)
Theoretically, a Tafel slope, attained by experimental results, can suggest the
dominant reaction mechanism during a HER process.2121. Y. Shi and B. Zhang, “
Recent advances in transition metal phosphide nanomaterials: Synthesis and
applications in hydrogen evolution reaction,” Chem. Soc. Rev. 45(6), 1529–1541
(2016). https://doi.org/10.1039/C5CS00434A When a Tafel slope of 118 mV dec−1 is
observed, the rate-determining step is the electrochemical adsorption/reduction
step and the corresponding mechanism is called the Volmer mechanism. If the
Tafel value is 39 or 28 mV dec−1, the first step is fast and the Heyrovsky or
Tafel reaction is the rate-determining step, respectively, corresponding to the
Volmer–Heyrovsky or Volmer–Tafel mechanism, respectively.
B. Proposed volcano-type curves
Electrochemical hydrogen adsorption and desorption on the active sites of the
material surface essentially belong to a couple of competitive reactions. Thus,
a suitable bonding strength, neither too weak nor too strong, between catalysts
and hydrogen species is of critical significance for a desired HER catalyst.
From a physicochemical point of view, the free energy of hydrogen adsorption
(ΔGH*) can synchronously disclose both the abilities of Hads adsorption and H2
desorption during a HER process.2222. T. F. Jaramillo, K. P. Jørgensen, J.
Bonde, J. H. Nielsen, S. Horch, and I. Chorkendorff, “ Identification of active
edge sites for electrochemical H2 evolution from MoS2 nanocatalysts,” Science
317(5834), 100–102 (2007). https://doi.org/10.1126/science.1141483 Based on the
well-acknowledged Sabatier principle, ideally, the largest HER j0 (j0 refers to
the exchange current density) can be achieved at ΔGH* = 0.2323. G. Zhang, K. V.
Vasudevan, B. L. Scott, and S. K. Hanson, “ Understanding the mechanisms of
cobalt-catalyzed hydrogenation and dehydrogenation reactions,” J. Am. Chem. Soc.
135(23), 8668–8681 (2013). https://doi.org/10.1021/ja402679a Later, a volcano
model was built up by correlating the j0 value with ΔGH* obtained from the
quantum chemistry. In this model, ΔGH* equals to zero at the peak point of the
volcano. The positive or negative ΔGH* values, respectively, mean too weak or
too strong adsorption of Hads on the catalyst surface, thus contributing to a
weakened HER performance, i.e., a decreased j0 [Fig. 3(a)].2424. R. Parsons, “
The rate of electrolytic hydrogen evolution and the heat of adsorption of
hydrogen,” Trans. Faraday Soc. 54, 1053–1063 (1958).
https://doi.org/10.1039/tf9585401053 Furthermore, Trasatti et al. proposed a
similar volcano-like curve to associate the log j0 values to the metal–hydrogen
(M–H) bond energy, as described in Fig. 3(b).25,2625. S. Trasatti, “ Work
function, electronegativity, and electrochemical behaviour of metals: III.
Electrolytic hydrogen evolution in acid solutions,” J. Electroanal. Chem.
Interfacial Electrochem. 39(1), 163–184 (1972).
https://doi.org/10.1016/S0022-0728(72)80485-626. T. R. Cook, D. K. Dogutan, S.
Y. Reece, Y. Surendranath, T. S. Teets, and D. G. Nocera, “ Solar energy supply
and storage for the legacy and nonlegacy worlds,” Chem. Rev. 110(11), 6474–6502
(2010). https://doi.org/10.1021/cr100246c Recently, with the rapid advancement
of this computational science field, the updated volcano-shaped trend was
presented with these experimental j0 values as a function of the density
functional theory (DFT)-derived ΔGH*, typically the one proposed by Nørskov et
al., as seen from Fig. 3(c).27,2827. J. K. Nørskov, T. Bligaard, A. Logadottir,
J. Kitchin, J. G. Chen, S. Pandelov, and U. Stimming, “ Trends in the exchange
current for hydrogen evolution,” J. Electrochem. Soc. 152(3), J23–J26 (2005).
https://doi.org/10.1149/1.185698828. E. Skúlason, V. Tripkovic, M. E. Björketun,
S. Gudmundsdottir, G. Karlberg, J. Rossmeisl, T. Bligaard, H. Jónsson, and J. K.
Nørskov, “ Modeling the electrochemical hydrogen oxidation and evolution
reactions on the basis of density functional theory calculations,” J. Phys.
Chem. C 114(42), 18182–18197 (2010). https://doi.org/10.1021/jp1048887
FIG. 3. Proposed volcano-type curves (a) based on HER activity (log j0) vs
adsorption energies (ΔGH*), (b) between log j0 and M–H binding energy on the
surface of several metals, or (c) based on the relationship of log j0 and ΔGH*
of various metals. (a) Reproduced with permission from Parsons et al., Trans.
Faraday Soc. 54, 1053–1063 (1958). Copyright 1958 Royal Society of Chemistry.
(b) Reproduced with permission from Cook et al., Chem. Rev. 110(11), 6474–6502
(2010). Copyright 2010 American Chemical Society. (c) Reproduced with permission
from Skúlason et al., J. Phys. Chem. C 114(42), 18182–18197 (2010). Copyright
2010 American Chemical Society.
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* High-resolution
III. BRIEF OVERVIEW OF THE HER ELECTROCATALYSTS BASED ON NON-PT NMNs
Section:
ChooseTop of pageABSTRACTI. INTRODUCTIONII. FUNDAMENTALS OF THE H...III. BRIEF
OVERVIEW OF TH... <<IV. CONSTRUCTING ROBUST N...V. NEW TRENDS IN THE ELEC...VI.
CONCLUSIONS AND OUTLO...Choose
Non-Pt noble metals with appropriate surface properties have already emerged as
attractive and promising catalytic materials for their super catalytic behaviors
in various chemical reactions, e.g., CO oxidation, methanol
reforming/decomposition, hydrodesulfurization, OER, HER, etc.29–3329. S. W.
Chee, J. M. Arce-Ramos, W. Li, A. Genest, and U. Mirsaidov, “ Structural changes
in noble metal nanoparticles during CO oxidation and their impact on catalyst
activity,” Nat. Commun. 11, 2133 (2020).
https://doi.org/10.1038/s41467-020-16027-930. B. Hasa, J. Vakros, and A. D.
Katsaounis, “ Effect of TiO2 on Pt-Ru-based anodes for methanol
electroreforming,” Appl. Catal. B 237(5), 811–816 (2018).
https://doi.org/10.1016/j.apcatb.2018.06.05531. Q.-Y. Hu, R.-H. Zhang, D. Chen,
Y.-F. Guo, W. Zhan, L.-M. Luo, and X.-W. Zhou, “ Facile aqueous phase synthesis
of 3D-netlike Pd-Rh nanocatalysts for methanol oxidation,” Int. J. Hydrogen
Energy 44(31), 16287–16296 (2019).
https://doi.org/10.1016/j.ijhydene.2019.05.04832. H. Ziaei-Azad and N. Semagina,
“ Iridium addition enhances hydrodesulfurization selectivity in
4,6-dimethyldibenzothiophene conversion on palladium,” Appl. Catal. B 191(15),
138–146 (2016). https://doi.org/10.1016/j.apcatb.2016.03.02333. Q. Shi, C. Zhu,
D. Du, and Y. Lin, “ Robust noble metal-based electrocatalysts for oxygen
evolution reaction,” Chem. Soc. Rev. 48(12), 3181–3192 (2019).
https://doi.org/10.1039/C8CS00671G In a catalyzing HER, the principle shown in
Fig. 3 well guides the design of the electrocatalysts, which presents the
observations from theoretical and experimental investigations. Remarkably, these
non-Pt noble metals, mainly including Pd, Rh, and Ir, position close to Pt, that
is, approximately at the apex of this volcano-like diagram.27,2827. J. K.
Nørskov, T. Bligaard, A. Logadottir, J. Kitchin, J. G. Chen, S. Pandelov, and U.
Stimming, “ Trends in the exchange current for hydrogen evolution,” J.
Electrochem. Soc. 152(3), J23–J26 (2005). https://doi.org/10.1149/1.185698828.
E. Skúlason, V. Tripkovic, M. E. Björketun, S. Gudmundsdottir, G. Karlberg, J.
Rossmeisl, T. Bligaard, H. Jónsson, and J. K. Nørskov, “ Modeling the
electrochemical hydrogen oxidation and evolution reactions on the basis of
density functional theory calculations,” J. Phys. Chem. C 114(42), 18182–18197
(2010). https://doi.org/10.1021/jp1048887 Thus, they own the most appropriate
ΔGH*, approaching zero, which makes them the most efficient catalysts for the
HER.27,2827. J. K. Nørskov, T. Bligaard, A. Logadottir, J. Kitchin, J. G. Chen,
S. Pandelov, and U. Stimming, “ Trends in the exchange current for hydrogen
evolution,” J. Electrochem. Soc. 152(3), J23–J26 (2005).
https://doi.org/10.1149/1.185698828. E. Skúlason, V. Tripkovic, M. E. Björketun,
S. Gudmundsdottir, G. Karlberg, J. Rossmeisl, T. Bligaard, H. Jónsson, and J. K.
Nørskov, “ Modeling the electrochemical hydrogen oxidation and evolution
reactions on the basis of density functional theory calculations,” J. Phys.
Chem. C 114(42), 18182–18197 (2010). https://doi.org/10.1021/jp1048887 As the
principle proposed by Trasatti et al. explains, the suitable hydrogen
adsorption/desorption at the metal surface can be well indicated by the moderate
M–H bond energy (∼65 kcal mol−1).25,2625. S. Trasatti, “ Work function,
electronegativity, and electrochemical behaviour of metals: III. Electrolytic
hydrogen evolution in acid solutions,” J. Electroanal. Chem. Interfacial
Electrochem. 39(1), 163–184 (1972).
https://doi.org/10.1016/S0022-0728(72)80485-626. T. R. Cook, D. K. Dogutan, S.
Y. Reece, Y. Surendranath, T. S. Teets, and D. G. Nocera, “ Solar energy supply
and storage for the legacy and nonlegacy worlds,” Chem. Rev. 110(11), 6474–6502
(2010). https://doi.org/10.1021/cr100246c Ru metal has this analogous Ru–H bond
strength of about 65 kcal mol−1, which enables a super catalytic behavior of Ru
as a HER electrocatalyst.1212. J. Yu, Q. He, G. Yang, W. Zhou, Z. Shao, and M.
Ni, “ Recent advances and prospective in ruthenium-based materials for
electrochemical water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b02457 For the other two noble metals, i.e.,
Au and Ag, their much weak adsorption energy of hydrogen suggests their
relatively low HER catalytic efficiency. However, the satisfactory performance
on them is sometimes caused by the structural and electronic optimization. To be
noted, based on the catalyst design strategies shown in Fig. 2, these
outstanding nanostructured non-Pt noble metal-based materials have unique
electronic configuration, versatile composition, novel micro-morphology,
tailorable chemical valence, etc., which are substantially associated with the
number of active sites and the reaction energy barrier of catalytic reactions.
Eventually, the admirable catalytic properties are achieved on these non-Pt
NMNs. Aiming at these great outcomes, the next section focuses on the discussion
of various electronic modulation and structural design tactics to propel the
catalytic performance.
IV. CONSTRUCTING ROBUST NON-PT NOBLE METAL-BASED ELECTROCATALYSTS TOWARD THE HER
Section:
ChooseTop of pageABSTRACTI. INTRODUCTIONII. FUNDAMENTALS OF THE H...III. BRIEF
OVERVIEW OF TH...IV. CONSTRUCTING ROBUST N... <<V. NEW TRENDS IN THE ELEC...VI.
CONCLUSIONS AND OUTLO...Choose
A. Element composition optimization
1. Noble-metal-based alloys
Incorporation of other alien metals into the lattice of a given metal has been
identified to be a versatile and impactful pathway in boosting the HER
electrocatalytic performance owing to the ligand effects and cumulative strain
from the changed bond energy and bond length, endowing favorable electronic
structure and adsorption energy of hydrogen intermediates.16,17,34–4816. P.
Jiang, H. Huang, J. Diao, S. Gong, S. Chen, J. Lu, C. Wang, Z. Sun, G. Xia, and
K. Yang, “ Improving electrocatalytic activity of iridium for hydrogen evolution
at high current densities above 1000 mA cm−2,” Appl. Catal. B 258(5), 117965
(2019). https://doi.org/10.1016/j.apcatb.2019.11796517. J. Feng, F. Lv, W.
Zhang, P. Li, K. Wang, C. Yang, B. Wang, Y. Yang, J. Zhou, and F. Lin, “
Iridium-based multimetallic porous hollow nanocrystals for efficient
overall-water-splitting catalysis,” Adv. Mater. 29(47), 1703798 (2017).
https://doi.org/10.1002/adma.20170379834. M. Zhu, Q. Shao, Y. Qian, and X.
Huang, “ Superior overall water splitting electrocatalysis in acidic conditions
enabled by bimetallic Ir-Ag nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.02335. R.-Q. Yao, Y.-T. Zhou, H. Shi,
Q.-H. Zhang, L. Gu, Z. Wen, X.-Y. Lang, and Q. Jiang, “ Nanoporous
palladium-silver surface alloys as efficient and pH-universal catalysts for the
hydrogen evolution reaction,” ACS Energy Lett. 4(6), 1379–1386 (2019).
https://doi.org/10.1021/acsenergylett.9b0084536. W. Choi, G. Hu, K. Kwak, M.
Kim, D-e Jiang, J.-P. Choi, and D. Lee, “ Effects of metal-doping on hydrogen
evolution reaction catalyzed by MAu24 and M2Au36 nanoclusters (M = Pt, Pd,” ACS
Appl. Mater. Interfaces 10(51), 44645–44653 (2018).
https://doi.org/10.1021/acsami.8b1617837. Y. Qin, X. Dai, X. Zhang, X. Huang, H.
Sun, D. Gao, Y. Yu, P. Zhang, Y. Jiang, and H. Zhuo, “ Microwave-assisted
synthesis of multiply-twinned Au-Ag nanocrystals on reduced graphene oxide for
high catalytic performance towards hydrogen evolution reaction,” J. Mater. Chem.
A 4(10), 3865–3871 (2016). https://doi.org/10.1039/C5TA10428A38. L. Chang, D.
Cheng, L. Sementa, and A. Fortunelli, “ Hydrogen evolution reaction (HER) on
Au@Ag ultrananoclusters as electro-catalysts,” Nanoscale 10(37), 17730–17737
(2018). https://doi.org/10.1039/C8NR06105J39. X. Qin, L. Zhang, G.-L. Xu, S.
Zhu, Q. Wang, M. Gu, X. Zhang, C. Sun, P. B. Balbuena, and K. Amine, “ The role
of Ru in improving the activity of Pd toward hydrogen evolution and oxidation
reactions in alkaline solutions,” ACS Catal. 9(10), 9614–9621 (2019).
https://doi.org/10.1021/acscatal.9b0174440. W. Shen, B. Wu, F. Liao, B. Jiang,
and M. Shao, “ Optimizing the hydrogen evolution reaction by shrinking Pt amount
in Pt-Ag/SiNW nanocomposites,” Int. J. Hydrogen Energy 42(22), 15024–15030
(2017). https://doi.org/10.1016/j.ijhydene.2017.03.11041. T. Chao, X. Luo, W.
Chen, B. Jiang, J. Ge, Y. Lin, G. Wu, X. Wang, Y. Hu, and Z. Zhuang, “
Atomically dispersed copper-platinum dual sites alloyed with palladium nanorings
catalyze the hydrogen evolution reaction,” Angew. Chem., Int. Ed. 129(50),
16263–16267 (2017). https://doi.org/10.1002/ange.20170980342. J. Lu, L. Zhang,
S. Jing, L. Luo, and S. Yin, “ Remarkably efficient PtRh alloyed with nanoscale
WC for hydrogen evolution in alkaline solution,” Int. J. Hydrogen Energy 42(9),
5993–5999 (2017). https://doi.org/10.1016/j.ijhydene.2017.01.18143. K. Li, Y.
Li, Y. Wang, J. Ge, C. Liu, and W. Xing, “ Enhanced electrocatalytic performance
for the hydrogen evolution reaction through surface enrichment of platinum
nanoclusters alloying with ruthenium in situ embedded in carbon,” Energy
Environ. Sci. 11(5), 1232–1239 (2018). https://doi.org/10.1039/C8EE00402A44. L.
Li, G. Zhang, B. Wang, T. Yang, and S. Yang, “ Electrochemical formation of PtRu
bimetallic nanoparticles for highly efficient and pH-universal hydrogen
evolution reaction,” J. Mater. Chem. A 8(4), 2090–2098 (2020).
https://doi.org/10.1039/C9TA12300H45. L. Zhang, H. Liu, S. Liu, M. Norouzi
Banis, Z. Song, J. Li, L. Yang, M. Markiewicz, Y. Zhao, and R. Li, “ Pt/Pd
single-atom alloys as highly active electrochemical catalysts and the origin of
enhanced activity,” ACS Catal. 9(10), 9350–9358 (2019).
https://doi.org/10.1021/acscatal.9b0167746. C. H. Chen, D. Wu, Z. Li, R. Zhang,
C. G. Kuai, X. R. Zhao, C. K. Dong, S. Z. Qiao, H. Liu, and X. W. Du, “
Ruthenium-based single-atom alloy with high electrocatalytic activity for
hydrogen evolution,” Adv. Energy Mater. 9(20), 1803913 (2019).
https://doi.org/10.1002/aenm.20180391347. J. Mao, C.-T. He, J. Pei, W. Chen, D.
He, Y. He, Z. Zhuang, C. Chen, Q. Peng, and D. Wang, “ Accelerating water
dissociation kinetics by isolating cobalt atoms into ruthenium lattice,” Nat.
Commun. 9, 4958 (2018). https://doi.org/10.1038/s41467-018-07288-648. J. Li, F.
Li, S.-X. Guo, J. Zhang, and J. Ma, “ PdCu@Pd nanocube with Pt-like activity for
hydrogen evolution reaction,” ACS Appl. Mater. Interfaces 9(9), 8151–8160
(2017). https://doi.org/10.1021/acsami.7b01241 Therefore, plenty of alloy
materials have been developed.
a. Noble metal–noble metal alloys
Noble–noble metallic alloys have been proven to express highly enhanced
catalytic activity for the HER.34–3834. M. Zhu, Q. Shao, Y. Qian, and X. Huang,
“ Superior overall water splitting electrocatalysis in acidic conditions enabled
by bimetallic Ir-Ag nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.02335. R.-Q. Yao, Y.-T. Zhou, H. Shi,
Q.-H. Zhang, L. Gu, Z. Wen, X.-Y. Lang, and Q. Jiang, “ Nanoporous
palladium-silver surface alloys as efficient and pH-universal catalysts for the
hydrogen evolution reaction,” ACS Energy Lett. 4(6), 1379–1386 (2019).
https://doi.org/10.1021/acsenergylett.9b0084536. W. Choi, G. Hu, K. Kwak, M.
Kim, D-e Jiang, J.-P. Choi, and D. Lee, “ Effects of metal-doping on hydrogen
evolution reaction catalyzed by MAu24 and M2Au36 nanoclusters (M = Pt, Pd,” ACS
Appl. Mater. Interfaces 10(51), 44645–44653 (2018).
https://doi.org/10.1021/acsami.8b1617837. Y. Qin, X. Dai, X. Zhang, X. Huang, H.
Sun, D. Gao, Y. Yu, P. Zhang, Y. Jiang, and H. Zhuo, “ Microwave-assisted
synthesis of multiply-twinned Au-Ag nanocrystals on reduced graphene oxide for
high catalytic performance towards hydrogen evolution reaction,” J. Mater. Chem.
A 4(10), 3865–3871 (2016). https://doi.org/10.1039/C5TA10428A38. L. Chang, D.
Cheng, L. Sementa, and A. Fortunelli, “ Hydrogen evolution reaction (HER) on
Au@Ag ultrananoclusters as electro-catalysts,” Nanoscale 10(37), 17730–17737
(2018). https://doi.org/10.1039/C8NR06105J Zhu et al. explored the hollow Ir–Ag
alloy nanotubes (NTs) as the HER catalysts in acidic media and demonstrated a
considerable catalytic activity, showing an overpotential of only 20 mV at a 10
mA cm−2 current density in the acidic environment.3434. M. Zhu, Q. Shao, Y.
Qian, and X. Huang, “ Superior overall water splitting electrocatalysis in
acidic conditions enabled by bimetallic Ir-Ag nanotubes,” Nano Energy 56,
330–337 (2019). https://doi.org/10.1016/j.nanoen.2018.11.023 Yao and his
co-workers illustrated that Ag doping in the Pd–Ag alloy surface well regulated
the electronic structure of the monometallic Pd surface, which in turn balanced
the reaction rates of water-dissociation and hydrogen-formation steps toward
boosting the HER performance.3535. R.-Q. Yao, Y.-T. Zhou, H. Shi, Q.-H. Zhang,
L. Gu, Z. Wen, X.-Y. Lang, and Q. Jiang, “ Nanoporous palladium-silver surface
alloys as efficient and pH-universal catalysts for the hydrogen evolution
reaction,” ACS Energy Lett. 4(6), 1379–1386 (2019).
https://doi.org/10.1021/acsenergylett.9b00845 The strength of Pd–H against the
Had combination into H2 in the HER was largely mitigated to an appropriate value
after the incorporation of Ag atoms, as shown in Fig. 4(a), that was, at the
Pd–Pd–Ag hollow sites, the value of hydrogen binding energy (HBE) (−0.49 eV) was
very close to that of Pt (111). Meanwhile, Qin et al. also confirmed the
optimization of HER performance in basic media by devising alloyed Pd3Ru
nanoparticles with several Ru segregations on the surface.3939. X. Qin, L.
Zhang, G.-L. Xu, S. Zhu, Q. Wang, M. Gu, X. Zhang, C. Sun, P. B. Balbuena, and
K. Amine, “ The role of Ru in improving the activity of Pd toward hydrogen
evolution and oxidation reactions in alkaline solutions,” ACS Catal. 9(10),
9614–9621 (2019). https://doi.org/10.1021/acscatal.9b01744 They elucidated the
effect of Ru dopants in HBE and the adsorption of OH−, which consequently
lowered the energy barrier of the reaction-determining step in the HER process.
As reported by Choi and his co-workers, the atomically Pd or Pt-doped MAu24 and
M2Au36 nanocrystals further helped reintroduce the effect mechanism of metal
doping.3636. W. Choi, G. Hu, K. Kwak, M. Kim, D-e Jiang, J.-P. Choi, and D. Lee,
“ Effects of metal-doping on hydrogen evolution reaction catalyzed by MAu24 and
M2Au36 nanoclusters (M = Pt, Pd,” ACS Appl. Mater. Interfaces 10(51),
44645–44653 (2018). https://doi.org/10.1021/acsami.8b16178 The authors found
that upon introducing Pd/Pt atoms into Au25 or Au38 nanoclusters (NCs), their
electrochemical redox potentials were altered to enable an efficient electron
transfer and hence controlled the onset potentials. Furthermore, through
theoretical simulations, they offered a trend on the basis of ΔGH for varied
metal-doped Au nanoclusters. In line with the calculated ΔGH values,
electrochemical experiments evidenced that the doping impact on HER catalytic
activity, reflected by the catalytic current density and turnover frequency
(TOF), followed this order of Pt > Pd > undoped counterpart.
FIG. 4. (a) HBE values on different active sites obtained through DFT
calculations. Reproduced with permission from Yao et al., ACS Energy Lett. 4(6),
1379–1386 (2019). Copyright 2019 American Chemical Society. (b)
Linear-sweep-voltammetry (LSV) curves toward the HER for various samples,
including Pd nanosheets, Pd/Cu NRs, Pd/Cu–Pt NRs, and benchmark Pt/C, under
acidic conditions. (c) and (d) The k3-weighted c(k)-function of EXAFS spectra
for (c) Pt L3-edge and (d) Cu K-edge. Reproduced with permission from Chao et
al., Angew. Chem., Int. Ed. 129(50), 16263–16267 (2017). Copyright 2017
Wiley-VCH.
* PPT
|
* High-resolution
Among the noble-metal-based combinations, alloying with Pt shows a particular
interest. Besides the as-referred Pt–Au alloy, alloyed Pt–Ag, Pt–Pd, Pt–Rh, and
Pt–Ir materials also have been extensively studied for the HER
catalysis.40–4440. W. Shen, B. Wu, F. Liao, B. Jiang, and M. Shao, “ Optimizing
the hydrogen evolution reaction by shrinking Pt amount in Pt-Ag/SiNW
nanocomposites,” Int. J. Hydrogen Energy 42(22), 15024–15030 (2017).
https://doi.org/10.1016/j.ijhydene.2017.03.11041. T. Chao, X. Luo, W. Chen, B.
Jiang, J. Ge, Y. Lin, G. Wu, X. Wang, Y. Hu, and Z. Zhuang, “ Atomically
dispersed copper-platinum dual sites alloyed with palladium nanorings catalyze
the hydrogen evolution reaction,” Angew. Chem., Int. Ed. 129(50), 16263–16267
(2017). https://doi.org/10.1002/ange.20170980342. J. Lu, L. Zhang, S. Jing, L.
Luo, and S. Yin, “ Remarkably efficient PtRh alloyed with nanoscale WC for
hydrogen evolution in alkaline solution,” Int. J. Hydrogen Energy 42(9),
5993–5999 (2017). https://doi.org/10.1016/j.ijhydene.2017.01.18143. K. Li, Y.
Li, Y. Wang, J. Ge, C. Liu, and W. Xing, “ Enhanced electrocatalytic performance
for the hydrogen evolution reaction through surface enrichment of platinum
nanoclusters alloying with ruthenium in situ embedded in carbon,” Energy
Environ. Sci. 11(5), 1232–1239 (2018). https://doi.org/10.1039/C8EE00402A44. L.
Li, G. Zhang, B. Wang, T. Yang, and S. Yang, “ Electrochemical formation of PtRu
bimetallic nanoparticles for highly efficient and pH-universal hydrogen
evolution reaction,” J. Mater. Chem. A 8(4), 2090–2098 (2020).
https://doi.org/10.1039/C9TA12300H According to Chao et al., atomically
dispersed Cu metal on Pd nanorings (NRs) was used as seeds for introducing Cu–Pt
dual sites into Pd NRs, in which the atom ratio of Pt is about 1.5%.4141. T.
Chao, X. Luo, W. Chen, B. Jiang, J. Ge, Y. Lin, G. Wu, X. Wang, Y. Hu, and Z.
Zhuang, “ Atomically dispersed copper-platinum dual sites alloyed with palladium
nanorings catalyze the hydrogen evolution reaction,” Angew. Chem., Int. Ed.
129(50), 16263–16267 (2017). https://doi.org/10.1002/ange.201709803 The
trimetallic alloy, namely Pd/Cu–Pt NRs, achieved exceptional HER performance
[Fig. 4(b)] because of atomically Cu–Pt active sites that were confirmed by the
presence of Cu–Pt coordination bonds as well as the absence of Pt–Pt and Cu–Cu
bonds from extended x-ray absorption fine structure (EXAFS) results shown in
Figs. 4(c) and 4(d). The comparison among H adsorption energies of different
metals, based on theoretical calculations, strongly supported the experimental
analysis. Most recently, Yang's group considered a Pt–Ru bimetallic nanoalloy as
the extraordinary HER catalyst in a broader pH range.4444. L. Li, G. Zhang, B.
Wang, T. Yang, and S. Yang, “ Electrochemical formation of PtRu bimetallic
nanoparticles for highly efficient and pH-universal hydrogen evolution
reaction,” J. Mater. Chem. A 8(4), 2090–2098 (2020).
https://doi.org/10.1039/C9TA12300H To control the Pt/Ru amount and realize a
homogeneous metal distribution, a novel simple electrochemical deposition (ECD)
technique was applied with RuO2 loaded on carbon cloth as the working electrode
and Pt mesh as the counter electrode, where trace Pt ions can be
electrochemically dissolved from the counter electrode and then were
electrochemically deposited on the working electrode. Owing to a synergistic
influence between Pt and Ru that resulted in boosted hydrogen desorption and
accelerated H2O dissociation, Pt–Ru bimetals supported on carbon cloth with an
optimum Pt amount presented a super good catalytic efficiency with the η10 of
only 8, 19, and 25 mV and the Tafel slopes of 25, 28, and 36 mV dec−1 in 0.5 M
H2SO4, 1 M KOH, and 1 M PBS, respectively. Analogously, Pt–Ru nanoalloys
embedded in porous spherical carbon were reported in a previous study by Xing's
group.4343. K. Li, Y. Li, Y. Wang, J. Ge, C. Liu, and W. Xing, “ Enhanced
electrocatalytic performance for the hydrogen evolution reaction through surface
enrichment of platinum nanoclusters alloying with ruthenium in situ embedded in
carbon,” Energy Environ. Sci. 11(5), 1232–1239 (2018).
https://doi.org/10.1039/C8EE00402A A precisely controlled polycondensation
reaction was employed for the production; but, several performance indices, such
as overpotential (19.7 mV in 0.5 M H2SO4 electrolytes), Tafel slope (27.2 mV
dec−1 in 0.5 M H2SO4 electrolytes), etc., significantly differed in view of the
discrepancies in the catalyst nanostructure and metal loading amounts.
For further increasing the alloy atom utilization efficiency, single-atom alloys
(SAAs) have been elaborately fabricated. However, such a single-atom form is
relatively difficult to obtain because of the metastable nanostructures and fast
crystallization growth rate.45,4645. L. Zhang, H. Liu, S. Liu, M. Norouzi Banis,
Z. Song, J. Li, L. Yang, M. Markiewicz, Y. Zhao, and R. Li, “ Pt/Pd single-atom
alloys as highly active electrochemical catalysts and the origin of enhanced
activity,” ACS Catal. 9(10), 9350–9358 (2019).
https://doi.org/10.1021/acscatal.9b0167746. C. H. Chen, D. Wu, Z. Li, R. Zhang,
C. G. Kuai, X. R. Zhao, C. K. Dong, S. Z. Qiao, H. Liu, and X. W. Du, “
Ruthenium-based single-atom alloy with high electrocatalytic activity for
hydrogen evolution,” Adv. Energy Mater. 9(20), 1803913 (2019).
https://doi.org/10.1002/aenm.201803913 Chen and his co-workers put forward a
rapid synthesis of alloyed RuAu single-atom catalysts using laser ablation in
liquid.4646. C. H. Chen, D. Wu, Z. Li, R. Zhang, C. G. Kuai, X. R. Zhao, C. K.
Dong, S. Z. Qiao, H. Liu, and X. W. Du, “ Ruthenium-based single-atom alloy with
high electrocatalytic activity for hydrogen evolution,” Adv. Energy Mater.
9(20), 1803913 (2019). https://doi.org/10.1002/aenm.201803913 During the
preparation process, a Ru target was first submerged in the mixed solution with
HAuCl4 and HCl, followed by irradiation using a nanosecond laser [Fig. 5(a)].
This treatment caused the Ru target vaporization and thermal decomposition of
HAuCl4, thus producing RuAu single-atom alloys after subsequent fast quenching.
Various types of RuAu single-atom alloys (SAAs), Ru, RuAu-0.1, RuAu-0.2,
RuAu-0.3, and RuAu-0.5, were synthesized by varied concentrations of HAuCl4. It
was found that there was an upper limit dissolution for Au atoms in these
nanoalloys here, i.e., RuAu-0.2. To create a current density of 10 mA cm−2 under
basic conditions, the required HER overpotential for the optimal RuAu-0.2 was
only 24 mV, which was 34 and 22 mV smaller than the data of Ru and Pt/C,
respectively [Fig. 5(b)]. Moreover, compared to Pt/C, RuAu-0.2 exhibited a
threefold higher TOF, being as high as 2.18 s−1 [Fig. 5(c)]. X-ray photoelectron
spectroscopy (XPS) and DFT calculations were carried out to unveil the origins
of such high activity. As illustrated in Fig. 5(d), RuAu SAAs promoted the HER
in the basic environment through the relay catalysis of Ru and Au active
centers, namely, water molecules were adsorbed and dissociated on Ru atoms, and
then Au atoms captured the released protons and accelerated the generation of
molecular hydrogen, as such, an ultrahigh catalytic activity for the alkaline
HER was attainable in the RuAu SAAs. Impressively, this synthesis method can be
generalized, even for the immiscible Ru and Ag in the solid state. Almost at the
same time, Zhang et al. deposited the trace Pt atoms on the Pd nanoparticles for
the surface formation of Pt–Pd single-atom alloys.4545. L. Zhang, H. Liu, S.
Liu, M. Norouzi Banis, Z. Song, J. Li, L. Yang, M. Markiewicz, Y. Zhao, and R.
Li, “ Pt/Pd single-atom alloys as highly active electrochemical catalysts and
the origin of enhanced activity,” ACS Catal. 9(10), 9350–9358 (2019).
https://doi.org/10.1021/acscatal.9b01677 The SSA nanostructure owned the highly
unoccupied density of states (DOSs) in the 5d character and greatly diminished
the H2 adsorption energy, correspondingly giving rise to a Pt-outperformed HER
catalytic performance in acidic media.
FIG. 5. (a) The preparation process of RuAu SAAs. (b) HER polarization curves of
the pure Au, Ru, and RuAu-0.2 electrocatalysts, in comparison with commercial
Pt/C, in 1 M KOH. (c) The corresponding TOF results at the overpotential of 50
mV. (d) A schematic illustrating the hydrogen-evolution process on RuAu SAAs.
These deep blue, silver gray, golden, red, and white and green balls indicate
the top layer of Ru, the bottom layer of Ru, Au, O, and H atoms, respectively.
Reproduced with permission from Chen et al., Adv. Energy Mater. 9(20), 1803913
(2019). Copyright 2019 Wiley-VCH.
* PPT
|
* High-resolution
b. Noble metal-transition metal alloys
As to these high-performance noble–noble metallic alloys, the high cost is still
an obstacle for wide commercial adoption. Aiming to handle this issue, the
precious metals, i.e., Ru, Rh, Pd, Ag, Ir, and Au, can form alloys with some
cheaper transition metals (TMs), with the dosage of these precious metals even
down up to an order of magnitude.16,17,47,4816. P. Jiang, H. Huang, J. Diao, S.
Gong, S. Chen, J. Lu, C. Wang, Z. Sun, G. Xia, and K. Yang, “ Improving
electrocatalytic activity of iridium for hydrogen evolution at high current
densities above 1000 mA cm−2,” Appl. Catal. B 258(5), 117965 (2019).
https://doi.org/10.1016/j.apcatb.2019.11796517. J. Feng, F. Lv, W. Zhang, P. Li,
K. Wang, C. Yang, B. Wang, Y. Yang, J. Zhou, and F. Lin, “ Iridium-based
multimetallic porous hollow nanocrystals for efficient overall-water-splitting
catalysis,” Adv. Mater. 29(47), 1703798 (2017).
https://doi.org/10.1002/adma.20170379847. J. Mao, C.-T. He, J. Pei, W. Chen, D.
He, Y. He, Z. Zhuang, C. Chen, Q. Peng, and D. Wang, “ Accelerating water
dissociation kinetics by isolating cobalt atoms into ruthenium lattice,” Nat.
Commun. 9, 4958 (2018). https://doi.org/10.1038/s41467-018-07288-648. J. Li, F.
Li, S.-X. Guo, J. Zhang, and J. Ma, “ PdCu@Pd nanocube with Pt-like activity for
hydrogen evolution reaction,” ACS Appl. Mater. Interfaces 9(9), 8151–8160
(2017). https://doi.org/10.1021/acsami.7b01241 Particularly, 3d TMs, such as Ni,
Co, Fe, Cu, and Mn, have been mixed with noble metals for upgrading the HER
activity.16,17,47–4916. P. Jiang, H. Huang, J. Diao, S. Gong, S. Chen, J. Lu, C.
Wang, Z. Sun, G. Xia, and K. Yang, “ Improving electrocatalytic activity of
iridium for hydrogen evolution at high current densities above 1000 mA cm−2,”
Appl. Catal. B 258(5), 117965 (2019).
https://doi.org/10.1016/j.apcatb.2019.11796517. J. Feng, F. Lv, W. Zhang, P. Li,
K. Wang, C. Yang, B. Wang, Y. Yang, J. Zhou, and F. Lin, “ Iridium-based
multimetallic porous hollow nanocrystals for efficient overall-water-splitting
catalysis,” Adv. Mater. 29(47), 1703798 (2017).
https://doi.org/10.1002/adma.20170379847. J. Mao, C.-T. He, J. Pei, W. Chen, D.
He, Y. He, Z. Zhuang, C. Chen, Q. Peng, and D. Wang, “ Accelerating water
dissociation kinetics by isolating cobalt atoms into ruthenium lattice,” Nat.
Commun. 9, 4958 (2018). https://doi.org/10.1038/s41467-018-07288-648. J. Li, F.
Li, S.-X. Guo, J. Zhang, and J. Ma, “ PdCu@Pd nanocube with Pt-like activity for
hydrogen evolution reaction,” ACS Appl. Mater. Interfaces 9(9), 8151–8160
(2017). https://doi.org/10.1021/acsami.7b0124149. Y. Liu, X. Li, Q. Zhang, W.
Li, Y. Xie, H. Liu, L. Shang, Z. Liu, Z. Chen, L. Gu, Z. Tang, T. Zhang, and S.
Lu, “ A general route to prepare low-ruthenium-content bimetallic
electrocatalysts for pH-universal hydrogen evolution reaction by using carbon
quantum dots,” Angew. Chem., Int. Ed. 59(4), 1718–1726 (2020).
https://doi.org/10.1002/anie.201913910 The electronegativity difference between
noble metals and TMs could lead to the d-band filling of noble metals,
accompanied by a negative shift in the d-band center, sequentially generating a
favorable electronic configuration that substantially accelerates performance
amelioration. Pi et al., using a facile wet-chemical method, prepared various
monodispersed IrM (M = Ni, Co, and Fe) nanoclusters (NCs) with mean sizes of
1.5–2 nm and systematically studied their catalytic performances.5050. Y. Pi, Q.
Shao, P. Wang, J. Guo, and X. Huang, “ General formation of monodisperse IrM
(M = Ni, Co, Fe) bimetallic nanoclusters as bifunctional electrocatalysts for
acidic overall water splitting,” Adv. Funct. Mater. 27(27), 1700886 (2017).
https://doi.org/10.1002/adfm.201700886 It was revealed that both HER and OER
activities increased in this trend, i.e., Ir NCs < IrFe NCs < IrCo NCs < IrNi
NCs, with IrNi NCs unleashing the best catalytic properties in acidic solutions
(ηonset = 210 mV for OER and η20 = 19 mV for HER) among these samples.
Nonetheless, there was no coverage of the underlying origins about such results
in this work. Afterwards, another case by Guo's group further supported the
boosting order on the catalytic activity for IrM (M = Ni and Co) alloys (Ir <
IrCo < IrNi) and found that the decreased hydrogen binding energy (HBE) should
be accountable for this trend.5151. F. Lv, W. Zhang, W. Yang, J. Feng, K. Wang,
J. Zhou, P. Zhou, and S. Guo, “ Ir-based alloy nanoflowers with optimized
hydrogen binding energy as bifunctional electrocatalysts for overall water
splitting,” Small Methods 4(6), 1900129 (2020).
https://doi.org/10.1002/smtd.201900129 Figure 6(a) described the potential
values of H sorption peaks through the CV curves in the Hupd (under potential
deposited H) region, which could mirror HBE. The obtained potentials followed
this sequence of IrNi < IrCo < Ir that was in accordance with the variation
tendency in their downshift of Ir 4f XPS peaks [Fig. 6(b)] and had an absolute
reciprocal relationship with their catalytic activities. Notwithstanding
relative to IrNi and IrCo, alloying Fe with Ir metal exhibited a minimum
activity enhancement; a regulated electronic structure along with d electron
couplings in IrFe still appeared to heavily raise HER activity in comparison
with pure Ir metal.1616. P. Jiang, H. Huang, J. Diao, S. Gong, S. Chen, J. Lu,
C. Wang, Z. Sun, G. Xia, and K. Yang, “ Improving electrocatalytic activity of
iridium for hydrogen evolution at high current densities above 1000 mA cm−2,”
Appl. Catal. B 258(5), 117965 (2019).
https://doi.org/10.1016/j.apcatb.2019.117965 Likewise, alloyed RhFe catalysts
with shortened Rh–Rh bonds also maneuvered the superior HER activity to the pure
Rh counterpart, announced by Golvano-Escobal et al.5252. I. Golvano-Escobal, S.
Suriñach, M. D. Baró, S. Pané, J. Sort, and E. Pellicer, “ Electrodeposition of
sizeable and compositionally tunable rhodium-iron nanoparticles and their
activity toward hydrogen evolution reaction,” Electrochim. Acta 194(10), 263–275
(2016). https://doi.org/10.1016/j.electacta.2016.02.112 and Zhang et al.5353. L.
Zhang, J. Lu, S. Yin, L. Luo, S. Jing, A. Brouzgou, J. Chen, P. K. Shen, and P.
Tsiakaras, “ One-pot synthesized boron-doped RhFe alloy with enhanced catalytic
performance for hydrogen evolution reaction,” Appl. Catal. B 230(15), 58–64
(2018). https://doi.org/10.1016/j.apcatb.2018.02.034 Very lately, Majee and
colleagues further emphasized the impacts of the doped-Ag proportion on HER
activities of AgNi alloys with decahedral geometry.5454. R. Majee, A. Kumar, T.
Das, S. Chakraborty, and S. Bhattacharyya, “ Tweaking nickel with minimal silver
in a heterogeneous alloy of decahedral geometry to deliver platinum-like
hydrogen evolution activity,” Angew. Chem., Int. Ed. 59(7), 2881–2889 (2020).
https://doi.org/10.1002/anie.201913704 The optimal ratio, of about 5 at. % Ag
(AgNi-5), in the decahedral AgNi alloys rationalized the site-specific element
distribution on the surface, where its faces were Ni-rich and Ag predominantly
resided at the apex and edges, and thereby gained maximum charge transport.
Toward HER, to arrive at a 10 mA cm−2 current density in 1 M KOH, AgNi-5
required a low overpotential of ∼24 mV, which was comparable to that of Pt/C. In
addition, there was no noticeable current change at the fixed potential of −0.15
V for 5 days. It is also worth to mention that the relative adsorption
capability of H species at the Ni centers was identified as a function of their
proximity to Ag atoms. In addition, annealing noble metal cations (Ru, Ir, or
Pd)-permeated Ni/Co-based metal-organic frameworks (MOFs) were broadly
demonstrated to yield the noble-transition metallic nanoalloy core implanted in
graphene-like carbon cages (nanoalloy@NC).55–5955. P. Jiang, J. Chen, C. Wang,
K. Yang, S. Gong, S. Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the
activity of carbon for electrocatalytic hydrogen evolution via an iridium-cobalt
alloy core encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9),
1705324 (2018). https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P.
Jiang, K. Yang, J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O
species-decorated graphene shell encapsulating iridium-nickel alloy as an
efficient electrocatalyst towards hydrogen evolution reaction,” J. Mater. Chem.
A 7(25), 15079–15088 (2019). https://doi.org/10.1039/C9TA04361F57. J. Chen, G.
Xia, P. Jiang, Y. Yang, R. Li, R. Shi, J. Su, and Q. Chen, “ Active and durable
hydrogen evolution reaction catalyst derived from Pd-doped metal-organic
frameworks,” ACS Appl. Mater. Interfaces 8(21), 13378–13383 (2016).
https://doi.org/10.1021/acsami.6b0126658. J. Su, Y. Yang, G. Xia, J. Chen, P.
Jiang, and Q. Chen, “ Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped
graphene as active electrocatalysts for producing hydrogen in alkaline media,”
Nat. Commun. 8, 14969 (2017). https://doi.org/10.1038/ncomms1496959. Y. Xu, S.
Yin, C. Li, K. Deng, H. Xue, X. Li, H. Wang, and L. Wang, “
Low-ruthenium-content NiRu nanoalloys encapsulated in nitrogen-doped carbon as
highly efficient and pH-universal electrocatalysts for the hydrogen evolution
reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H These nanoalloy@NC samples synthesized in
this way contained a very low noble metal loading (less than 2 wt. %) and yet
exhibited extraordinary catalytic behavior toward the HER.55–5955. P. Jiang, J.
Chen, C. Wang, K. Yang, S. Gong, S. Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “
Tuning the activity of carbon for electrocatalytic hydrogen evolution via an
iridium-cobalt alloy core encapsulated in nitrogen-doped carbon cages,” Adv.
Mater. 30(9), 1705324 (2018). https://doi.org/10.1002/adma.20170532456. S. Gong,
C. Wang, P. Jiang, K. Yang, J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O
species-decorated graphene shell encapsulating iridium-nickel alloy as an
efficient electrocatalyst towards hydrogen evolution reaction,” J. Mater. Chem.
A 7(25), 15079–15088 (2019). https://doi.org/10.1039/C9TA04361F57. J. Chen, G.
Xia, P. Jiang, Y. Yang, R. Li, R. Shi, J. Su, and Q. Chen, “ Active and durable
hydrogen evolution reaction catalyst derived from Pd-doped metal-organic
frameworks,” ACS Appl. Mater. Interfaces 8(21), 13378–13383 (2016).
https://doi.org/10.1021/acsami.6b0126658. J. Su, Y. Yang, G. Xia, J. Chen, P.
Jiang, and Q. Chen, “ Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped
graphene as active electrocatalysts for producing hydrogen in alkaline media,”
Nat. Commun. 8, 14969 (2017). https://doi.org/10.1038/ncomms1496959. Y. Xu, S.
Yin, C. Li, K. Deng, H. Xue, X. Li, H. Wang, and L. Wang, “
Low-ruthenium-content NiRu nanoalloys encapsulated in nitrogen-doped carbon as
highly efficient and pH-universal electrocatalysts for the hydrogen evolution
reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H A reasonable interpretation for the high
performance was proposed to be that the near-optimal adsorption energies for
H-related intermediates were achieved in these electrocatalysts based on the
modification of charge distribution on the N-doped graphene (NG-x) layer by
modulating metal cores.55,5655. P. Jiang, J. Chen, C. Wang, K. Yang, S. Gong, S.
Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the activity of carbon for
electrocatalytic hydrogen evolution via an iridium-cobalt alloy core
encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324 (2018).
https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K. Yang,
J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated graphene
shell encapsulating iridium-nickel alloy as an efficient electrocatalyst towards
hydrogen evolution reaction,” J. Mater. Chem. A 7(25), 15079–15088 (2019).
https://doi.org/10.1039/C9TA04361F For Cu-noble metal alloys, Li et al. observed
that a volcano relationship matched the HER catalytic activity trend with
increasing Cu content from x:y = 3:1 to 1:3 in PdxCuy.4848. J. Li, F. Li, S.-X.
Guo, J. Zhang, and J. Ma, “ PdCu@Pd nanocube with Pt-like activity for hydrogen
evolution reaction,” ACS Appl. Mater. Interfaces 9(9), 8151–8160 (2017).
https://doi.org/10.1021/acsami.7b01241 Pd1Cu1 stood out to be the best one in
0.5 M H2SO4. Similarly, Wang et al. synthesized Au–Cu alloy nanoparticles with
altered Cu proportion as prominent HER catalysts.6060. J. Wang, H. Zhu, D. Yu,
J. Chen, J. Chen, M. Zhang, L. Wang, and M. Du, “ Engineering the composition
and structure of bimetallic Au-Cu alloy nanoparticles in carbon nanofibers:
Self-supported electrode materials for electrocatalytic water splitting,” ACS
Appl. Mater. Interfaces 9(23), 19756–19765 (2017).
https://doi.org/10.1021/acsami.7b01418 The particle sizes ranged from 5 to 30 nm
and there were few morphology distinctions depending on the Cu content; but the
escalating Cu ratio transferred the homogeneous AuCu3 alloy phase to Au3Cu alloy
wrapped by a Cu coating. CuRu alloy was also a high-performance catalytic
material for the HER.49,6149. Y. Liu, X. Li, Q. Zhang, W. Li, Y. Xie, H. Liu, L.
Shang, Z. Liu, Z. Chen, L. Gu, Z. Tang, T. Zhang, and S. Lu, “ A general route
to prepare low-ruthenium-content bimetallic electrocatalysts for pH-universal
hydrogen evolution reaction by using carbon quantum dots,” Angew. Chem., Int.
Ed. 59(4), 1718–1726 (2020). https://doi.org/10.1002/anie.20191391061. Q. Wu, M.
Luo, J. Han, W. Peng, Y. Zhao, D. Chen, M. Peng, J. Liu, F. M. de Groot, and Y.
Tan, “ Identifying electrocatalytic sites of the nanoporous copper-ruthenium
alloy for hydrogen evolution reaction in alkaline electrolyte,” ACS Energy Lett.
5(1), 192–199 (2020). https://doi.org/10.1021/acsenergylett.9b02374 A little
while ago, Wu et al. identified the actual electrocatalytic sites of the HER in
nanoporous CuRu alloys that were manufactured by a simple dealloying process
[Fig. 6(c)].6161. Q. Wu, M. Luo, J. Han, W. Peng, Y. Zhao, D. Chen, M. Peng, J.
Liu, F. M. de Groot, and Y. Tan, “ Identifying electrocatalytic sites of the
nanoporous copper-ruthenium alloy for hydrogen evolution reaction in alkaline
electrolyte,” ACS Energy Lett. 5(1), 192–199 (2020).
https://doi.org/10.1021/acsenergylett.9b02374 In the dealloying route, a
single-phase ternary Ru3Cu22Mn75 alloy was treated in (NH4)2SO4 solution to
remove all Mn and partial Cu, so then to obtain the nanoporous CuRu alloys. In
situ x-ray absorption spectroscopy (XAS) measurements in conjunction with
theoretical calculations elucidated that the combination of Cu and Ru reinforced
the Cu–H interaction whilst weakened the strength of the Ru–H bond to
dramatically enhance the HER efficiency, of which the water-splitting barrier
and hydrogen adsorption energy were reduced to −0.551 eV and 0.092 eV,
respectively [Figs. 6(d) and 6(e)]. Here, these, together with accelerated
charge/ions migration in the interconnected porous structure, were thought to be
dominant reasons for a remarkable HER catalytic behavior in terms of small η10
(∼15 and ∼41 mV) and Tafel slopes (∼30 and ∼35 mV dec−1) in both basic and
neutral solutions, respectively.
FIG. 6. (a) H sorption peaks in the Hupd region for different reported samples
in acidic media. (b) Ir 4f XPS peaks for different materials. Reproduced with
permission from Lv et al., Small Methods 4(6), 1900129 (2020). Copyright 2020
Wiley-VCH. (c) Diagrammatic illustration of the synthesis route of nanoporous
CuRu alloys. (d) The calculated water-splitting barriers and (e) hydrogen
adsorption energy results. Reproduced with permission from Wu et al., ACS Energy
Lett. 5(1), 192–199 (2019). Copyright 2019 American Chemical Society.
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Mo and W also have been introduced into the noble metal structures and their
impacts on electrocatalysis have been investigated.62,6362. F. Lv, J. Feng, K.
Wang, Z. Dou, W. Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “
Iridium-tungsten alloy nanodendrites as pH-universal water-splitting
electrocatalysts,” ACS Cent. Sci. 4(9), 1244–1252 (2018).
https://doi.org/10.1021/acscentsci.8b0042663. Z. Zhang, P. Li, Q. Wang, Q. Feng,
Y. Tao, J. Xu, C. Jiang, X. Lu, J. Fan, and M. Gu, “ Mo modulation effect on the
hydrogen binding energy of hexagonal-close-packed Ru for hydrogen evolution,” J.
Mater. Chem. A 7(6), 2780–2786 (2019). https://doi.org/10.1039/C8TA11251G Guo's
group reported a nanodendritic-like Ir–W alloy (IrW ND), prepared by a
colloidal–chemical approach with IrCl3·xH2O and W(CO)6 as metal sources,
cetyltrimethylammonium chloride (CTAC) as the surfactant, glucose as a reducing
agent, and oleylamine as the solvent.6262. F. Lv, J. Feng, K. Wang, Z. Dou, W.
Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “ Iridium-tungsten alloy
nanodendrites as pH-universal water-splitting electrocatalysts,” ACS Cent. Sci.
4(9), 1244–1252 (2018). https://doi.org/10.1021/acscentsci.8b00426 The raw
materials were first mixed under ultrasonication and underwent heat treatment in
a capped vial. When compared to the monometallic Ir, the IrW ND sample offered a
strengthened HER efficiency in both the acid and base, with η10 = 12 and 29 mV
and the TOF values of 3.75 and 2.16 s−1 at the 10 mV overpotential, respectively
[Figs. 7(a) and 7(b)]. Moreover, this hydrogen generation rate was even twice
better than that obtained from the Pt catalyst [Figs. 7(a) and 7(b)]. The
theoretical analysis based on DFT pointed out the key factors in improvement of
HER performance in different electrolytes [Figs. 7(c) and 7(d)]: a stronger H
adsorption of the surface Ir site in IrW relative to Ir facilitated hydrogen
evolution in acid, while the higher alkaline HER activity was due to a higher
affinity to OH to the W site toward accelerating the dissociation of water.
Additionally, the authors also found a remarkable increase in OER
electrocatalytic activity and stability upon W doping, and they ascribed such a
phenomenon to the weakened binding energy of oxygen intermediates and the
stabilized active iridium oxides formed in the course of the OER. Later, Zhang
and his co-workers verified that heteroatom Mo doping positively modified the
hydrogen adsorption energy in the hcp-structured Ru metal and resulted in
considerable promotion on the HER activity.6363. Z. Zhang, P. Li, Q. Wang, Q.
Feng, Y. Tao, J. Xu, C. Jiang, X. Lu, J. Fan, and M. Gu, “ Mo modulation effect
on the hydrogen binding energy of hexagonal-close-packed Ru for hydrogen
evolution,” J. Mater. Chem. A 7(6), 2780–2786 (2019).
https://doi.org/10.1039/C8TA11251G
FIG. 7. The overpotentials at a current density of 10 mA cm−2 and TOF values at
10 mV overpotential of this IrW/C sample and the commercial Ir/C and Pt/C
catalysts in both the (a) acid and (b) base. (c) Diagram showing the HER
mechanism under acidic and alkaline conditions on the surface of IrW NDs. (d)
Relationship between HER activity and H or OH binding energies on IrW and Ir
electrocatalysts. Reproduced with permission from Lv et al., ACS Cent. Sci.
4(9), 1244–1252 (2018). Copyright 2018 American Chemical Society. (e) OER and
(f) HER polarization curves of these Co–RuIr, Ni–RuIr, Fe–RuIr, and RuIr samples
in 0.1 M HClO4 electrolytes. Dependence of (g) OH− desorption potential and OER
activity on intensity of OI− species and (h) HUPD potential and HER activity on
Ru binding energy. Reproduced with permission from Shan et al., Adv. Mater.
31(17), 1900510 (2019). Copyright 2019 Wiley-VCH.
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For the sake of extending the combination of metals, several ternary alloy
systems have also been exploited.64–6864. L. Fu, G. Cheng, and W. Luo, “
Colloidal synthesis of monodisperse trimetallic IrNiFe nanoparticles as highly
active bifunctional electrocatalysts for acidic overall water splitting,” J.
Mater. Chem. A 5(47), 24836–24841 (2017). https://doi.org/10.1039/C7TA08982A65.
Z. J. Wang, M. X. Li, J. H. Yu, X. B. Ge, Y. H. Liu, and W. H. Wang, “
Low-iridium-content IrNiTa metallic glass films as intrinsically active
catalysts for hydrogen evolution reaction,” Adv. Mater. 32(4), 1906384 (2020).
https://doi.org/10.1002/adma.20190638466. H. Li, Q. Tang, B. He, and P. Yang, “
Robust electrocatalysts from an alloyed Pt-Ru-M (M = Cr, Fe, Co, Ni,
Mo)-decorated Ti mesh for hydrogen evolution by seawater splitting,” J. Mater.
Chem. A 4(17), 6513–6520 (2016). https://doi.org/10.1039/C6TA00785F67. J. Shan,
T. Ling, K. Davey, Y. Zheng, and S. Z. Qiao, “ Transition-metal-doped RuIr
bifunctional nanocrystals for overall water splitting in acidic environments,”
Adv. Mater. 31(17), 1900510 (2019). https://doi.org/10.1002/adma.20190051068. D.
Zhang, H. Zhao, B. Huang, B. Li, H. Li, Y. Han, Z. Wang, X. Wu, Y. Pan, and Y.
Sun, “ Advanced ultrathin RuPdM (M = Ni, Co, Fe) nanosheets electrocatalyst
boosts hydrogen evolution,” ACS Cent. Sci. 5(12), 1991–1997 (2019).
https://doi.org/10.1021/acscentsci.9b01110 For example, an IrNiTa metallic glass
(MG) nanofilm with low iridium content was studied as an intrinsically highly
active catalyst for producing hydrogen.6565. Z. J. Wang, M. X. Li, J. H. Yu, X.
B. Ge, Y. H. Liu, and W. H. Wang, “ Low-iridium-content IrNiTa metallic glass
films as intrinsically active catalysts for hydrogen evolution reaction,” Adv.
Mater. 32(4), 1906384 (2020). https://doi.org/10.1002/adma.201906384 The author
suggested that a synergy between the suitable alloy composition and amorphous
nanostructure brought about the high performance. Shan and colleagues added
different transition metals (Co, Ni, or Fe) into the RuIr alloy
nanostructure.6767. J. Shan, T. Ling, K. Davey, Y. Zheng, and S. Z. Qiao, “
Transition-metal-doped RuIr bifunctional nanocrystals for overall water
splitting in acidic environments,” Adv. Mater. 31(17), 1900510 (2019).
https://doi.org/10.1002/adma.201900510 The dependency of OER and HER catalytic
properties on the dopant types was subsequently established in detail [Figs.
7(e) and 7(f)]. The optimal Co doping induced the creation of more
low-coordinated oxygen species and altered the surface valence states of Ru and
Ir that give rise to the modified binding strength of oxygen/hydrogen
intermediates [Figs. 7(g) and 7(h)]. Thus, following Co doping of the RuIr
alloy, the Co–RuIr sample significantly expedited the HER and OER rates in 0.1 M
HClO4 electrolytes, leading to low overpotentials of 14 mV for HER and 235 mV
for OER at 10 mA cm−2 [Figs. 7(e) and 7(f)]. Eventually, a cell voltage of only
1.52 V at a current density of 10 mA cm−2 was observed for total water
electrolysis. Analogously, a series of different transition metals (Ni, Co, and
Fe) doped-RuPd alloys with ultrathin nanosheet (NS) structures were reported in
a recent work by Zhang et al., which gave excellent HER catalytic activities in
basic solutions.6868. D. Zhang, H. Zhao, B. Huang, B. Li, H. Li, Y. Han, Z.
Wang, X. Wu, Y. Pan, and Y. Sun, “ Advanced ultrathin RuPdM (M = Ni, Co, Fe)
nanosheets electrocatalyst boosts hydrogen evolution,” ACS Cent. Sci. 5(12),
1991–1997 (2019). https://doi.org/10.1021/acscentsci.9b01110 As to the optimized
Ru38Pd34Ni28 NSs, the overpotential was just 20 mV at a current density of 10 mA
cm−2 and the mass activity at −0.07 V vs reversible hydrogen electrode (RHE) was
up to 6.15 A mg−1noble metal. Good cycling stability was also obtained. Note
that this mass activity was 9.6 folds and 88 folds higher than the results in
Pt/C and Pd/C catalysts, respectively, becoming the largest one among various
non-Pt materials studied so far. From DFT results, a significant electronic
structure regulation by incorporating the transition metals (Fe, Co, and Ni) to
RuPd NSs was uncovered, specifically showing a linear upshifting of d-band
center from −2.5 eV to −1.5 eV. In particular, continuous electron replenishment
from metal Ni ensured a fast electron transfer toward adsorbates.
Simultaneously, stable Pd active sites strengthened p–d coupling in the initial
water dissociation with a facile activation barrier.
2. Noble-metal-based compounds
The electrocatalytic properties of noble metal-based materials could often be
manipulated by constructing novel compounds, containing metal oxides,
phosphides, dichalcogenides, borides, carbides, and the like.69–7369. Z. Zhuang,
Y. Wang, C.-Q. Xu, S. Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S.
Lu, “ Three-dimensional open nano-netcage electrocatalysts for efficient
pH-universal overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-070. J. Yu, X. Wu, H. Zhang, M. Ni, W.
Zhou, and Z. Shao, “ Core effect on the performance of N/P codoped carbon
encapsulating noble-metal phosphide nanostructures for hydrogen evolution
reaction,” ACS Appl. Energy Mater. 2(4), 2645–2653 (2019).
https://doi.org/10.1021/acsaem.8b0224971. J. Yu, Y. Guo, S. Miao, M. Ni, W.
Zhou, and Z. Shao, “ Spherical ruthenium disulfide-sulfur-doped graphene
composite as an efficient hydrogen evolution electrocatalyst,” ACS Appl. Mater.
Interfaces 10(40), 34098–34107 (2018). https://doi.org/10.1021/acsami.8b0823972.
Q. Li, X. Zou, X. Ai, H. Chen, L. Sun, and X. Zou, “ Revealing activity trends
of metal diborides toward pH-universal hydrogen evolution electrocatalysts with
Pt-like activity,” Adv. Energy Mater. 9(5), 1803369 (2018).
https://doi.org/10.1002/aenm.20180336973. T. Wakisaka, K. Kusada, D. Wu, T.
Yamamoto, T. Toriyama, S. Matsumura, H. Akiba, O. Yamamuro, K. Ikeda, and T.
Otomo, “ Rational synthesis for a noble metal carbide,” J. Am. Chem. Soc.
142(3), 1247–1253 (2020). https://doi.org/10.1021/jacs.9b09219 Generally, every
compound inherited distinctive properties that tempted diverse catalytic active
sites.
a. Noble-metal-based oxides (NMOs)
Noble-metal-related oxides, especially IrO2 and RuO2, which are proverbially
used as benchmark OER catalysts, also have been applied to catalyze the HER in
some studies.74–7874. J. Ahmed and Y. Mao, “ Ultrafine iridium oxide nanorods
synthesized by molten salt method toward electrocatalytic oxygen and hydrogen
evolution reactions,” Electrochim. Acta 212(10), 686–693 (2016).
https://doi.org/10.1016/j.electacta.2016.06.12275. Y.-B. Cho, A. Yu, C. Lee, M.
H. Kim, and Y. Lee, “ Fundamental study of facile and stable hydrogen evolution
reaction at electrospun Ir and Ru mixed oxide nanofibers,” ACS Appl. Mater.
Interfaces 10(1), 541–549 (2018). https://doi.org/10.1021/acsami.7b1439976. J.
Yu, X. Wu, D. Guan, Z. Hu, S.-C. Weng, H. Sun, Y. Song, R. Ran, W. Zhou, and M.
Ni, “ Monoclinic SrIrO3: An easily-synthesized conductive perovskite oxide with
outstanding performance for overall water splitting in alkaline solution,” Chem.
Mater. 32(11), 4509–4517 (2020).
https://doi.org/10.1021/acs.chemmater.0c0014977. J. Wang, Y. Ji, R. Yin, Y. Li,
Q. Shao, and X. Huang, “ Transition metal-doped ultrathin RuO2 networked
nanowires for efficient overall water splitting across a broad pH range,” J.
Mater. Chem. A 7(11), 6411–6416 (2019). https://doi.org/10.1039/C9TA00598F78. Y.
Zhu, H. A. Tahini, Z. Hu, J. Dai, Y. Chen, H. Sun, W. Zhou, M. Liu, S. C. Smith,
and H. Wang, “ Unusual synergistic effect in layered Ruddlesden-Popper oxide
enables ultrafast hydrogen evolution,” Nat. Commun. 10, 149 (2019).
https://doi.org/10.1038/s41467-018-08117-6 As stated by our previous report,
several ruthenium-based oxides, including RuO2 nanorods, hydrous RuO2,
heteroatom (Fe, Co, Ni, Cu, etc.)-doped RuO2, Ruddlesden–Popper-type Sr2RuO4,
etc., were highly efficient for HER catalysis.1212. J. Yu, Q. He, G. Yang, W.
Zhou, Z. Shao, and M. Ni, “ Recent advances and prospective in ruthenium-based
materials for electrochemical water splitting,” ACS Catal. 9(11), 9973–10011
(2019). https://doi.org/10.1021/acscatal.9b02457 Besides, Kundu et al. disclosed
that Rh2O3 provided stronger adsorption of OH−, thus facilitating adsorptive
dissociation of water and in turn HER activity.7979. M. K. Kundu, R. Mishra, T.
Bhowmik, and S. Barman, “ Rhodium metal-rhodium oxide (Rh-Rh2O3) nanostructures
with Pt-like or better activity towards hydrogen evolution and oxidation
reactions (HER, HOR) in acid and base: Correlating its HOR/HER activity with
hydrogen binding energy and oxophilicity of the catalyst,” J. Mater. Chem. A
6(46), 23531–23541 (2018). https://doi.org/10.1039/C8TA07028H Very recently,
Li's group successfully synthesized hollow RuIrOx nanonetcages by using a
dispersing-etching-holing multistep strategy.6969. Z. Zhuang, Y. Wang, C.-Q. Xu,
S. Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S. Lu, “
Three-dimensional open nano-netcage electrocatalysts for efficient pH-universal
overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-0 Specifically, as illustrated in Fig.
8(a), with MOF ZIF-8 as an etchable parent material, initially an ion exchange
readily occurred between Zn2+ in it and free Ru3+/Ir4+; subsequently, through a
solvothermal reaction, these Ru3+/Ir4+/Zn2+ cations underwent hydrolysis along
with a gradual etching of the ZIF-8 internal core, which yielded nanosized
hollow boxes followed by a further calcination to achieve the homogeneous
RuIrZnOx oxides; lastly, an electrochemical in situ etching treatment was
implemented to remove amphoteric ZnO from RuIrZnOx, yielding the final RuIrOx
nanonetcage structures. Figures 8(b)–8(d) exhibited the representative
high-angle annular dark-field scanning transmission electron microscopy
(HAADF-STEM) images of RuIrOx nanonetcages, which attested the highly porous
walls with the pore size of 1–4 nm constituted by interconnected ultrathin
nanowires (NWs) (2–4 nm in width). This synthetic protocol endowed the porous
netcage-like nanoframework with a plethora of exposed active centers and a
three-dimensional accessibility toward substrate molecules. Accordingly, there
was a threefold or fivefold larger electrochemically active surface area (ECSA)
in the RuIrOx nanonetcages with respect to commercial Ir/C and Ru/C
particulates, respectively. Moreover, on the basis of DFT analysis and operando
XAS results, two attractive features were observed for this RuIrOx material.
First, the energy barriers for the potential limiting steps in HER and OER
processes were remarkably lowered, in which the H adsorption energy was just
−0.07 eV [Figs. 9(a) and 9(b)]. Second, electrons were migrated from Ir atoms to
Ru atoms, inhibiting Ru from over-oxidation [Figs. 9(c) and 9(d)] and high
valence state Ir was believed to help to oxygen evolution. All these permitted
this nanonetcage catalyst to deliver a superior HER/OER activity (HER: 13 mV at
pH = 14 and 12 mV at pH = 0 and OER: 250 mV at pH = 14 and 233 mV at pH = 0.)
and stability (all: negligible fluctuation in activity after a 3000 cycling
test) in both alkaline and acidic environments. Meanwhile, there are nearly no
studies on silver/gold/palladium oxides for the application toward HER
catalysis, most presumably owing to their relatively low activities.
FIG. 8. (a) The synthetic procedure of hollow RuIrOx nanonetcages. (b)–(d) The
representative HAADF-STEM images of RuIrOx nanonetcages. The scale bar is 10, 5,
and 2 nm, respectively. Reproduced with permission from Zhuang et al., Nat.
Commun. 10, 4875 (2019). Copyright 2019 Nature Publishing Group.
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FIG. 9. The free energy diagrams of the (a) HER and (b) OER on the surface of
various catalytic materials. The H, O, Ir, and Ru atoms are represented by pink,
red, gray, and gold balls, respectively. Normalized in situ x-ray absorption
near-edge structure (XANES) spectra for (c) Ru K-edge and (d) Ir L3-edge of the
RuIrOx sample, which were obtained at different OER operating potentials in the
acidic media. Reproduced with permission from Zhuang et al., Nat. Commun. 10,
4875 (2019). Copyright 2019 Nature Publishing Group. (e) TEM image of w-Rh2P NS.
The inset is its selected area electron diffraction (SAED) image. (f) LSV curves
of the as-prepared w-Rh2P NS, Rh NS, and commercial Pt/C for HER in 0.1 M KOH.
Reproduced with permission from Wang et al., Adv. Energy Mater. 8(27), 1801891
(2018). Copyright 2018 Wiley-VCH.
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b. Noble-metal-based phosphides
Since 2017, when Li's group and Mu's group pronounced that Rh2P and RuP2-based
materials featured a suitable hydrogen adsorption energy and hence granted
superior HER activities in a wide range of pH,80,8180. H. Duan, D. Li, Y. Tang,
Y. He, S. Ji, R. Wang, H. Lv, P. P. Lopes, A. P. Paulikas, and H. Li, “
High-performance Rh2P electrocatalyst for efficient water splitting,” J. Am.
Chem. Soc. 139(15), 5494–5502 (2017). https://doi.org/10.1021/jacs.7b0137681. Z.
Pu, I. S. Amiinu, Z. Kou, W. Li, and S. Mu, “ RuP2-based catalysts with
platinum-like activity and higher durability for the hydrogen evolution reaction
at all pH values,” Angew. Chem., Int. Ed. 56(38), 11559–11564 (2017).
https://doi.org/10.1002/anie.201704911 ample efforts have been made on noble
metal phosphides, especially rhodium phosphides (RhPx, i.e., Rh2P, RhP2, etc.)
and ruthenium phosphides (RuPx, i.e., RhP2, RuP, Ru2P, etc.), for hydrogen
evolution.82–8782. Q. Qin, H. Jang, L. Chen, G. Nam, X. Liu, and J. Cho, “ Low
loading of RhxP and RuP on N, P codoped carbon as two trifunctional
electrocatalysts for the oxygen and hydrogen electrode reactions,” Adv. Energy
Mater. 8(29), 1801478 (2018). https://doi.org/10.1002/aenm.20180147883. Z. Pu,
I. S. Amiinu, D. He, M. Wang, G. Li, and S. Mu, “ Activating rhodium
phosphide-based catalysts for the pH-universal hydrogen evolution reaction,”
Nanoscale 10(26), 12407–12412 (2018). https://doi.org/10.1039/C8NR02854K84. K.
Wang, B. Huang, F. Lin, F. Lv, M. Luo, P. Zhou, Q. Liu, W. Zhang, C. Yang, and
Y. Tang, “ Wrinkled Rh2P nanosheets as superior pH-universal electrocatalysts
for hydrogen evolution catalysis,” Adv. Energy Mater. 8(27), 1801891 (2018).
https://doi.org/10.1002/aenm.20180189185. F. Yang, Y. Zhao, Y. Du, Y. Chen, G.
Cheng, S. Chen, and W. Luo, “ A monodisperse Rh2P-based electrocatalyst for
highly efficient and pH-universal hydrogen evolution reaction,” Adv. Energy
Mater. 8(18), 1703489 (2018). https://doi.org/10.1002/aenm.20170348986. J. Q.
Chi, X. J. Zeng, X. Shang, B. Dong, Y. M. Chai, C. G. Liu, M. Marin, and Y. Yin,
“ Embedding RhPx in N, P co-doped carbon nanoshells through synergetic
phosphorization and pyrolysis for efficient hydrogen evolution,” Adv. Funct.
Mater. 29(33), 1901790 (2019). https://doi.org/10.1002/adfm.20190179087. J. Yu,
Y. Guo, S. She, S. Miao, M. Ni, W. Zhou, M. Liu, and Z. Shao, “ Bigger is
surprisingly better: Agglomerates of larger RuP nanoparticles outperform
benchmark Pt nanocatalysts for the hydrogen evolution reaction,” Adv. Mater.
30(39), 1800047 (2018). https://doi.org/10.1002/adma.201800047 In 2018, Guo's
group put forward the design of wrinkled Rh2P nanosheets (w-Rh2P NS) with an
ultrathin thickness of ∼ 3.3 nm [Fig. 9(e)] based on a two-step chemical
solvothermal procedure, in which Rh nanosheets were first obtained by heating
the mixture of rhodium acetylacetonate [Rh(acac)3], nickel acetylacetonate
[Ni(acac)2], L-ascorbic acid (AA), hexacarbonylmolybdenum [Mo(CO)6], and
oleylamine (OAm) at 180 °C in an oil bath and then these nanosheets were
phosphorized at 300 °C with the help of tri-n-octylphosphine (TOP) in the N2
environment.8484. K. Wang, B. Huang, F. Lin, F. Lv, M. Luo, P. Zhou, Q. Liu, W.
Zhang, C. Yang, and Y. Tang, “ Wrinkled Rh2P nanosheets as superior pH-universal
electrocatalysts for hydrogen evolution catalysis,” Adv. Energy Mater. 8(27),
1801891 (2018). https://doi.org/10.1002/aenm.201801891 Such resultant w-Rh2P NS
recorded a decent HER behavior in 0.1 M KOH with a η10 of 18.3 mV, which was
40.1 and 50.6 mV lower than those of commercial Pt/C and Rh NS, respectively,
[Fig. 9(f)] and a relatively low Tafel slope of 61.5 mV dec−1. With the support
from theoretical calculations on density of state (DOS) and free energies, the
in-depth catalytic mechanism in base was revealed, in which the P-3p orbital
with the active open-shell property boosted up Rh-4d for augmented
proton–electron charge exchange via orbital Coulombic interactions and also the
lower-lying 3p-σ bonding level ensured the anchoring of O-related species as an
excellent distributary center, so as to avail HER performance under alkaline
conditions. Moreover, the w-Rh2P NS sample was also highly efficient for HER
catalysis in acidic and neutral environments. Similarly, around the same time,
the remarkable electrocatalytic activity for pH-universal HER in Rh2P was
further verified by Yang et al. using monodisperse Rh2P nanoparticles, which was
prepared by a colloidal method with Rh(acac)3 and TOP as Rh and P sources.8585.
F. Yang, Y. Zhao, Y. Du, Y. Chen, G. Cheng, S. Chen, and W. Luo, “ A
monodisperse Rh2P-based electrocatalyst for highly efficient and pH-universal
hydrogen evolution reaction,” Adv. Energy Mater. 8(18), 1703489 (2018).
https://doi.org/10.1002/aenm.201703489 In our group, the RuP nanoparticles,
obtained by a simple phosphidation of RuCl3 in PH3 from NaH2PO2, demonstrated a
phenomenal catalytic performance in all pH media.8787. J. Yu, Y. Guo, S. She, S.
Miao, M. Ni, W. Zhou, M. Liu, and Z. Shao, “ Bigger is surprisingly better:
Agglomerates of larger RuP nanoparticles outperform benchmark Pt nanocatalysts
for the hydrogen evolution reaction,” Adv. Mater. 30(39), 1800047 (2018).
https://doi.org/10.1002/adma.201800047 Surprisingly, we found that bigger RuP
nanoparticles exhibited larger intrinsic activity and stability compared to the
small ones, which might be derived from the stabilization of P species due to a
lowered surface energy in large nanoparticles. It is noteworthy that, with a
controllably equivalent nanostructure, the RuP catalyst performed more excellent
than RuP2 in terms of HER activity, as a result of more catalytically active
centers and higher electric conductivity of RuP.88,8988. Q. Chang, J. Ma, Y.
Zhu, Z. Li, D. Xu, X. Duan, W. Peng, Y. Li, G. Zhang, and F. Zhang, “
Controllable synthesis of ruthenium phosphides (RuP and RuP2) for pH-universal
hydrogen evolution reaction,” ACS Sustainable Chem. Eng. 6(5), 6388–6394 (2018).
https://doi.org/10.1021/acssuschemeng.8b0018789. R. Ge, S. Wang, J. Su, Y. Dong,
Y. Lin, Q. Zhang, and L. Chen, “ Phase-selective synthesis of self-supported RuP
films for efficient hydrogen evolution electrocatalysis in alkaline media,”
Nanoscale 10(29), 13930–13935 (2018). https://doi.org/10.1039/C8NR03554G
Additionally, several mixed RhPx or RuPx phases, acting as catalytic materials,
were also reported with remarkable HER properties at all pH ranges.82,86,9082.
Q. Qin, H. Jang, L. Chen, G. Nam, X. Liu, and J. Cho, “ Low loading of RhxP and
RuP on N, P codoped carbon as two trifunctional electrocatalysts for the oxygen
and hydrogen electrode reactions,” Adv. Energy Mater. 8(29), 1801478 (2018).
https://doi.org/10.1002/aenm.20180147886. J. Q. Chi, X. J. Zeng, X. Shang, B.
Dong, Y. M. Chai, C. G. Liu, M. Marin, and Y. Yin, “ Embedding RhPx in N, P
co-doped carbon nanoshells through synergetic phosphorization and pyrolysis for
efficient hydrogen evolution,” Adv. Funct. Mater. 29(33), 1901790 (2019).
https://doi.org/10.1002/adfm.20190179090. J. Q. Chi, W. K. Gao, J. H. Lin, B.
Dong, K. L. Yan, J. F. Qin, B. Liu, Y. M. Chai, and C. G. Liu, “ Hydrogen
evolution activity of ruthenium phosphides encapsulated in nitrogen-and
phosphorous-codoped hollow carbon nanospheres,” ChemSusChem 11(4), 743–752
(2018). https://doi.org/10.1002/cssc.201702010 Under the identical synthesis
conditions, it was claimed that RhP2 was more active for catalyzing the HER than
RuP2 in acidic media, while this trend was reversed in alkaline
electrolytes.7070. J. Yu, X. Wu, H. Zhang, M. Ni, W. Zhou, and Z. Shao, “ Core
effect on the performance of N/P codoped carbon encapsulating noble-metal
phosphide nanostructures for hydrogen evolution reaction,” ACS Appl. Energy
Mater. 2(4), 2645–2653 (2019). https://doi.org/10.1021/acsaem.8b02249
Other noble-metal phosphides, like IrP2, PdP2, etc., were also proven to deliver
a splendid HER performance.91,9291. Z. Pu, J. Zhao, I. S. Amiinu, W. Li, M.
Wang, D. He, and S. Mu, “ A universal synthesis strategy for P-rich noble metal
diphosphide-based electrocatalysts for the hydrogen evolution reaction,” Energy
Environ. Sci. 12(3), 952–957 (2019). https://doi.org/10.1039/C9EE00197B92. F.
Luo, Q. Zhang, X. Yu, S. Xiao, Y. Ling, H. Hu, L. Guo, Z. Yang, L. Huang, and W.
Cai, “ Palladium phosphide as a stable and efficient electrocatalyst for overall
water splitting,” Angew. Chem., Int. Ed. 57(45), 14862–14867 (2018).
https://doi.org/10.1002/anie.201810102 However, so far, it is very rare to find
reports on them compared with that on RhPx or RuPx. Encouraged by a
close-to-zero proton adsorption energy in PdP2, Luo et al. developed a material
of palladium phosphides deposited on carbon black (PdP2@CB) by a facile
phosphorization pathway to study the HER properties.9292. F. Luo, Q. Zhang, X.
Yu, S. Xiao, Y. Ling, H. Hu, L. Guo, Z. Yang, L. Huang, and W. Cai, “ Palladium
phosphide as a stable and efficient electrocatalyst for overall water
splitting,” Angew. Chem., Int. Ed. 57(45), 14862–14867 (2018).
https://doi.org/10.1002/anie.201810102 A 10 mA cm−2 current density toward the
HER was reached by applying tiny overpotentials of 27.5, 35.4, and 84.6 mV in
0.5 M H2SO4, 1 M KOH, and 1 M PBS, all of which were comparable to that of Pt/C
(30.1, 46.6, and 122.7 mV, respectively) and much better than the Pd@CB under
the same conditions, manifesting the superb activity. Besides, PdP2@CB could be
in situ converted to Pd oxides/hydroxides under anodic oxidation voltage for
efficiently catalyzing the OER. According to the same research group that first
proposed the RuP2-based electrocatalyst, a novel iridium di-phosphide (IrP2)
catalyst encapsulated in an ultrathin N-doped carbon substrate (NC), denoted as
IrP2@NC, was further produced by direct calcination of mixed IrCl4, phytic acid
(PA), and melamine under Ar atmosphere.9191. Z. Pu, J. Zhao, I. S. Amiinu, W.
Li, M. Wang, D. He, and S. Mu, “ A universal synthesis strategy for P-rich noble
metal diphosphide-based electrocatalysts for the hydrogen evolution reaction,”
Energy Environ. Sci. 12(3), 952–957 (2019). https://doi.org/10.1039/C9EE00197B
The as-synthesized IrP2@NC sample afforded a vitally low HER overpotential of 8
and 28 mV at 10 mA cm−2 in the acidic and basic environments, respectively, far
below those of commercial Pt/C (18 and 42 mV, respectively), along with a highly
stable activity. The exceptional activity was mainly attributed to the lowered H
adsorption strength resulting from the combination of Ir and P and NC
introduction. To further extend the synthesis, the author also adopted this
method to obtain the two samples, RhP2@NC and Pd5P2@NC, showing the η10 of 29
and 249 mV in acid, respectively. Above all, cases stated that noble-metal
phosphides held great promise for HER applications.
c. Noble-metal-based chalcogenides
Noble-metal chalcogenides, a kind of novel HER catalytic material with
relatively low intrinsic electrical resistivity, have also been widely
investigated in the past few years, which mimicked the catalytic behavior of
benchmarking Pt almost over a whole pH range.93–10393. K. Wang, Q. Chen, Y. Hu,
W. Wei, S. Wang, Q. Shen, and P. Qu, “ Crystalline Ru0.33Se
nanoparticles-decorated TiO2 nanotube arrays for enhanced hydrogen evolution
reaction,” Small 14(37), 1802132 (2018).
https://doi.org/10.1002/smll.20180213294. P. Li, X. Duan, S. Wang, L. Zheng, Y.
Li, H. Duan, Y. Kuang, and X. Sun, “ Amorphous ruthenium-sulfide with isolated
catalytic sites for Pt-like electrocatalytic hydrogen production over whole pH
range,” Small 15(46), 1904043 (2019). https://doi.org/10.1002/smll.20190404395.
D. Yoon, B. Seo, J. Lee, K. S. Nam, B. Kim, S. Park, H. Baik, S. H. Joo, and K.
Lee, “ Facet-controlled hollow Rh2S3 hexagonal nanoprisms as highly active and
structurally robust catalysts toward hydrogen evolution reaction,” Energy
Environ. Sci. 9(3), 850–856 (2016). https://doi.org/10.1039/C5EE03456F96. P.
Hota, S. Bose, D. Dinda, P. Das, U. K. Ghorai, S. Bag, S. Mondal, and S. K.
Saha, “ Nickel-doped silver sulfide: An efficient air-stable electrocatalyst for
hydrogen evolution from neutral water,” ACS Omega 3(12), 17070–17076 (2018).
https://doi.org/10.1021/acsomega.8b0222397. J. Wang, L. Han, B. Huang, Q. Shao,
H. L. Xin, and X. Huang, “ Amorphization activated ruthenium-tellurium nanorods
for efficient water splitting,” Nat. Commun. 10, 5692 (2019).
https://doi.org/10.1038/s41467-019-13519-198. H. Huang, X. Fan, D. J. Singh, and
W. Zheng, “ Modulation of hydrogen evolution catalytic activity of basal plane
in monolayer platinum and palladium dichalcogenides,” ACS Omega 3(8),
10058–10065 (2018). https://doi.org/10.1021/acsomega.8b0141499. T. Zheng, C.
Shang, Z. He, X. Wang, C. Cao, H. Li, R. Si, B. Pan, S. Zhou, and J. Zeng, “
Intercalated iridium diselenide electrocatalysts for efficient pH-universal
water splitting,” Angew. Chem., Int. Ed. 131(41), 14906–14911 (2019).
https://doi.org/10.1002/ange.201909369100. Y. Zhu, H. A. Tahini, Y. Wang, Q.
Lin, Y. Liang, C. M. Doherty, Y. Liu, X. Li, J. Lu, and S. C. Smith, “
Pyrite-type ruthenium disulfide with tunable disorder and defects enables
ultra-efficient overall water splitting,” J. Mater. Chem. A 7(23), 14222–14232
(2019). https://doi.org/10.1039/C9TA04120F101. N. Singh, J. Hiller, H. Metiu,
and E. McFarland, “ Investigation of the electrocatalytic activity of rhodium
sulfide for hydrogen evolution and hydrogen oxidation,” Electrochim. Acta
145(1), 224–230 (2014). https://doi.org/10.1016/j.electacta.2014.09.012102. V.
Shokhen, Y. Kostikov, I. Borge-Durán, Y. Gershinsky, I. Grinberg, G. D. Nessim,
and D. Zitoun, “ Scalable silver oxo-sulfide catalyst for electrochemical water
splitting,” ACS Appl. Energy Mater. 2(1), 788–796 (2019).
https://doi.org/10.1021/acsaem.8b01844103. X. Zhang, Z. Luo, P. Yu, Y. Cai, Y.
Du, D. Wu, S. Gao, C. Tan, Z. Li, and M. Ren, “ Lithiation-induced amorphization
of Pd3P2S8 for highly efficient hydrogen evolution,” Nat. Catal. 1(6), 460–468
(2018). https://doi.org/10.1038/s41929-018-0072-y The initially exploited
Ru0.33Se nanoparticles loaded on TiO2 nanotube arrays actualized an efficient
activity for the HER in basic media with a η10 of 57 mV.9393. K. Wang, Q. Chen,
Y. Hu, W. Wei, S. Wang, Q. Shen, and P. Qu, “ Crystalline Ru0.33Se
nanoparticles-decorated TiO2 nanotube arrays for enhanced hydrogen evolution
reaction,” Small 14(37), 1802132 (2018). https://doi.org/10.1002/smll.201802132
Soon afterwards, our group fabricated high-crystalline and sphere-shape RuS2
particles on reduced graphene oxides (rGOs) by a facile solvothermal approach
followed by calcination treatment.7171. J. Yu, Y. Guo, S. Miao, M. Ni, W. Zhou,
and Z. Shao, “ Spherical ruthenium disulfide-sulfur-doped graphene composite as
an efficient hydrogen evolution electrocatalyst,” ACS Appl. Mater. Interfaces
10(40), 34098–34107 (2018). https://doi.org/10.1021/acsami.8b08239 Along with a
high intrinsic catalytic property in RuS2, the as-made material delivered a
remarkable HER catalytic performance over a wide pH range, comparing favorably
to the Pt/C sample. Also, recently, the amorphous structure of RuS2
nanoparticles was found to possess high Pt-like activities for catalyzing the
HER in pH-universal media by Li and co-workers, as elaborated below.9494. P. Li,
X. Duan, S. Wang, L. Zheng, Y. Li, H. Duan, Y. Kuang, and X. Sun, “ Amorphous
ruthenium-sulfide with isolated catalytic sites for Pt-like electrocatalytic
hydrogen production over whole pH range,” Small 15(46), 1904043 (2019).
https://doi.org/10.1002/smll.201904043 In another recent report, through tuning
the sulphuration temperature, both disorder and defects were synchronously
engineered in RuS2 nanoparticles.100100. Y. Zhu, H. A. Tahini, Y. Wang, Q. Lin,
Y. Liang, C. M. Doherty, Y. Liu, X. Li, J. Lu, and S. C. Smith, “ Pyrite-type
ruthenium disulfide with tunable disorder and defects enables ultra-efficient
overall water splitting,” J. Mater. Chem. A 7(23), 14222–14232 (2019).
https://doi.org/10.1039/C9TA04120F Benefiting from these controlled disorder and
defects, the electrochemically active surface area was enlarged and the
electronic structure was well modulated in a low-crystalline RuS2 material,
rendering an extraordinary catalytic activity for both the OER and HER in
alkaline solutions. DFT calculations unveiled that Ru vacancies drove the d-band
center of surface Ru upshift from −0.93 eV to −0.77 eV, which could reinforce
the H adsorption to an optimum level.
Toward other noble-metal chalcogenides, a pioneering work in 2014 by Singh et
al. demonstrated that Rh3S4 and Rh17S15 showed better HER activity than Rh2S3
and RhS2 phases.101101. N. Singh, J. Hiller, H. Metiu, and E. McFarland, “
Investigation of the electrocatalytic activity of rhodium sulfide for hydrogen
evolution and hydrogen oxidation,” Electrochim. Acta 145(1), 224–230 (2014).
https://doi.org/10.1016/j.electacta.2014.09.012 The active sites for HER on
these rhodium sulfides have been determined to be Rh rather than S atoms through
CO poisoning experiments coupled with DFT calculations. In 2016, Yoon et al.
engineered highly exposed edge sites in Rh2S3 by constructing hollow hexagonal
nanoprism shapes with well-defined facets and controlled size.9595. D. Yoon, B.
Seo, J. Lee, K. S. Nam, B. Kim, S. Park, H. Baik, S. H. Joo, and K. Lee, “
Facet-controlled hollow Rh2S3 hexagonal nanoprisms as highly active and
structurally robust catalysts toward hydrogen evolution reaction,” Energy
Environ. Sci. 9(3), 850–856 (2016). https://doi.org/10.1039/C5EE03456F In light
of this, an outstanding catalytic performance for the HER was endowed with
achieving a current density of 10 mA cm−2 by a small overpotential of 122 mV and
high stability under harsh acidic conditions. Shokhen et al. conducted
electrochemical activation on Ag2S to produce mesoporous silver covered by a
silver oxo-sulfide layer, which was highly active for hydrogen generation in 0.5
M H2SO4 and electrochemically or chemically stable over several days.102102. V.
Shokhen, Y. Kostikov, I. Borge-Durán, Y. Gershinsky, I. Grinberg, G. D. Nessim,
and D. Zitoun, “ Scalable silver oxo-sulfide catalyst for electrochemical water
splitting,” ACS Appl. Energy Mater. 2(1), 788–796 (2019).
https://doi.org/10.1021/acsaem.8b01844 Taking the merits of first-principle
calculation theory, Huang and his co-workers obtained this finding that on
monolayer PdSe2 and PdTe2, creating a double vacancy (DVSe and DVTe) and
boron-doping could appropriately regulate the interaction between the basal
plane and Hads species and upgraded the electrocatalytic hydrogen-evolving
activity of these metal dichalcogenides.9898. H. Huang, X. Fan, D. J. Singh, and
W. Zheng, “ Modulation of hydrogen evolution catalytic activity of basal plane
in monolayer platinum and palladium dichalcogenides,” ACS Omega 3(8),
10058–10065 (2018). https://doi.org/10.1021/acsomega.8b01414 Intrinsically,
IrSe2 is a quite ordinary HER electrocatalyst, displaying the η10 of 225, 371,
and 298 mV in these electrolytes with pH = 0, 7, and 14, respectively.9999. T.
Zheng, C. Shang, Z. He, X. Wang, C. Cao, H. Li, R. Si, B. Pan, S. Zhou, and J.
Zeng, “ Intercalated iridium diselenide electrocatalysts for efficient
pH-universal water splitting,” Angew. Chem., Int. Ed. 131(41), 14906–14911
(2019). https://doi.org/10.1002/ange.201909369 These values were decreased by as
much as around 200 mV using the intercalation of Li atoms, which could root in
abundant Se vacancies and high porosities. Besides, this tactic was also
applicable to reform the poor OER activity of IrSe2, evidenced by the η10
overpotential change from above 470 mV to below 320 mV at all pH ranges.
Simultaneously introducing sulfur and phosphorus into the palladium lattice
created a layered palladium thiophosphate (Pd3P2S8) material.103103. X. Zhang,
Z. Luo, P. Yu, Y. Cai, Y. Du, D. Wu, S. Gao, C. Tan, Z. Li, and M. Ren, “
Lithiation-induced amorphization of Pd3P2S8 for highly efficient hydrogen
evolution,” Nat. Catal. 1(6), 460–468 (2018).
https://doi.org/10.1038/s41929-018-0072-y Its crystalline phase is
electrochemically inert toward the HER. Zhang's group successfully applied an
electrochemical Li+ intercalation in a controllable galvanostatic lithiation
process to continuously alter the phase transition from crystal to amorphization
and introduced a plethora of P/S vacancies as well as heightened electrical
conductivity in the Pd3P2S8 sample, so as to gain the optimal atomic
configuration and electronic state toward HER performance [Figs.
10(a)–10(d)].103103. X. Zhang, Z. Luo, P. Yu, Y. Cai, Y. Du, D. Wu, S. Gao, C.
Tan, Z. Li, and M. Ren, “ Lithiation-induced amorphization of Pd3P2S8 for highly
efficient hydrogen evolution,” Nat. Catal. 1(6), 460–468 (2018).
https://doi.org/10.1038/s41929-018-0072-y Thereupon, a significant promotion in
HER catalysis was achieved. Specifically, at the identical electrocatalyst
loading, this onset overpotential value in 0.5 M H2SO4 was substantially reduced
from 175 mV of crystalline Pd3P2S8 to 52 mV of amorphous Li-incorporated Pd3P2S8
(Li-PPS), approaching to the value of Pt/C [Fig. 10(e)].
FIG. 10. (a) Atomic configuration (three-layer units) of Pd3P2S8 along the a
axis. (b) Coordination polyhedral structure of Pd3P2S8 along the c axis. (c) The
schematic of synthesis of the phase transition from crystal to amorphization
based on an electrochemical Li+ intercalation. (d) The atomic structure of the
resultant amorphous form along the c axis (left) and b axis (right). (e) HER
polarization curves of different as-obtained samples and commercial Pt/C in 0.5
M H2SO4. Reproduced with permission from Zhang et al., Nat. Catal. 1(6), 460–468
(2018). Copyright 2018 Nature Publishing Group.
* PPT
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* High-resolution
d. Noble-metal-based borides, carbides, or others
Similar to phosphides or chalcogenides, recently, noble-metal borides, carbides,
and silicides, have gained immense interests as potential HER
electrocatalysts.104–108104. L. Chen, L.-R. Zhang, L.-Y. Yao, Y.-H. Fang, L. He,
G.-F. Wei, and Z.-P. Liu, “ Metal boride better than Pt: HCP Pd2B as a
superactive hydrogen evolution reaction catalyst,” Energy Environ. Sci. 12(10),
3099–3105 (2019). https://doi.org/10.1039/C9EE01564G105. G. Wang, J. Liu, Y.
Sui, M. Wang, L. Qiao, F. Du, and B. Zou, “ Palladium structure engineering
induced by electrochemical H intercalation boosts hydrogen evolution catalysis,”
J. Mater. Chem. A 7(24), 14876–14881 (2019).
https://doi.org/10.1039/C9TA03971F106. H. Chen, X. Ai, W. Liu, Z. Xie, W. Feng,
W. Chen, and X. Zou, “ Promoting subordinate, efficient ruthenium sites with
interstitial silicon for Pt-like electrocatalytic activity,” Angew. Chem., Int.
Ed. 58(33), 11409–11413 (2019). https://doi.org/10.1002/anie.201906394107. J.
Fan, X. Cui, S. Yu, L. Gu, Q. Zhang, F. Meng, Z. Peng, L. Ma, J.-Y. Ma, and K.
Qi, “ Interstitial hydrogen atom modulation to boost hydrogen evolution in
Pd-based alloy nanoparticles,” ACS Nano 13(11), 12987–12995 (2019).
https://doi.org/10.1021/acsnano.9b05615108. S.-C. Lim, C.-Y. Chan, K.-T. Chen,
and H.-Y. Tuan, “ The shape-controlled synthesis of gallium-palladium (GaPd2)
nanomaterials as high-performance electrocatalysts for the hydrogen evolution
reaction,” Nanoscale 11(17), 8518–8527 (2019).
https://doi.org/10.1039/C8NR10536G For instance, Li and his co-workers presented
an innovative ruthenium diboride (RuB2) catalyst, that owned an appropriate
d-band center and a high density of superb active sites, thereby efficiently
catalyzing the HER process under pH-universal conditions.7272. Q. Li, X. Zou, X.
Ai, H. Chen, L. Sun, and X. Zou, “ Revealing activity trends of metal diborides
toward pH-universal hydrogen evolution electrocatalysts with Pt-like activity,”
Adv. Energy Mater. 9(5), 1803369 (2018). https://doi.org/10.1002/aenm.201803369
Based on a simple two-step solvothermal route with Pd acetylacetonate
[Pd(acac)2] and dimethylamine borane (DMAB) as Pd and B sources, respectively
[Fig. 11(a)], Chen et al. fabricated Pd2B nanosheets (NSs) as an acidic HER
catalyst.104104. L. Chen, L.-R. Zhang, L.-Y. Yao, Y.-H. Fang, L. He, G.-F. Wei,
and Z.-P. Liu, “ Metal boride better than Pt: HCP Pd2B as a superactive hydrogen
evolution reaction catalyst,” Energy Environ. Sci. 12(10), 3099–3105 (2019).
https://doi.org/10.1039/C9EE01564G Pd and B could form the bulk alloy with
atomic structure evolution from the fcc phase to hcp phase through varying the B
content, and Pd2B with a hcp structure was the thermodynamically most stable
phase [Fig. 11(b)], in which B lay at the octahedral interstitial sites (Oh) of
the Pd lattice [Fig. 11(c)]. This Pd2B sample achieved a η10 as small as 15.3 mV
with a low Tafel slope of 22.5 mV dec−1 and a large exchange current density of
2.84 mA cm−2, all of which significantly exceeded the Pd NS material and
benchmarking Pt catalyst. Besides, a long-term durability test revealed that
Pd2B NS could retain 97.6% activity after 12 h while the activities in Pd NS and
commercial Pt/C after 12 h were damped to 39.9% and 68.7%, respectively. As
analyzed from Figs. 11(d) and 11(e), the presence of subsurface B and the
lattice expansion after the hcp phase generation due to the B insertion, toward
promoting the H–H coupling, played pivotal roles in improving the HER
performance. Zou's group experimentally and theoretically validated that RuSi
was electrocatalytically active in producing hydrogen under acidic
conditions.106106. H. Chen, X. Ai, W. Liu, Z. Xie, W. Feng, W. Chen, and X. Zou,
“ Promoting subordinate, efficient ruthenium sites with interstitial silicon for
Pt-like electrocatalytic activity,” Angew. Chem., Int. Ed. 58(33), 11409–11413
(2019). https://doi.org/10.1002/anie.201906394 Thanks to its proper electronic
state administrated by a good balance of ligand and strain influence, this
material achieved 10 mA cm−2 by an overpotential of 19 mV and a small Tafel
slope of 28.9 mV dec−1. Most recently, a new and simple chemical–reduction
approach utilizing an organic oxidant, tetracyanoethylene (TCNE) as the carbon
source and inhibitor of Rh ion reduction, was engaged to evoke the formation of
Rh2C, which actualized marvelous efficiency in the HER due to a suitable H
adsorption energy, leading to a 13 mV overpotential at 5 mA cm−2.7373. T.
Wakisaka, K. Kusada, D. Wu, T. Yamamoto, T. Toriyama, S. Matsumura, H. Akiba, O.
Yamamuro, K. Ikeda, and T. Otomo, “ Rational synthesis for a noble metal
carbide,” J. Am. Chem. Soc. 142(3), 1247–1253 (2020).
https://doi.org/10.1021/jacs.9b09219 Together with these intermetallic
compounds, intermetallic MHx (M = precious metals) created by H intercalation
have also been investigated as catalytic materials for the HER and demonstrated
pronounced performance. In the RhPd alloy, interstitial H atom introduction
could tune the hydrogen adsorption energy to a desirable value by modulating the
surface electronic structure, bond length, and coordination numbers of Rh and
Pd, consequently resulting in a prominently enhanced alkaline HER
activity.107107. J. Fan, X. Cui, S. Yu, L. Gu, Q. Zhang, F. Meng, Z. Peng, L.
Ma, J.-Y. Ma, and K. Qi, “ Interstitial hydrogen atom modulation to boost
hydrogen evolution in Pd-based alloy nanoparticles,” ACS Nano 13(11),
12987–12995 (2019). https://doi.org/10.1021/acsnano.9b05615
FIG. 11. (a) Schematic illustration of producing Pd2B nanosheets. (b) The
formation energy of Pd–B alloy with varying B content through DFT calculations.
(c) Representative hcp Pd2B crystal structure. (d) The free energy profiles for
the HER process on different surfaces. (e) The structure change and free energy
barriers of the located transition states. Cyan: Pd atoms; pink: B atoms; white:
H atoms; light cyan: the reacting H atoms. Reproduced with permission from Chen
et al., Energy Environ. Sci. 12(10), 3099–3105 (2019). Copyright 2019 Royal
Society of Chemistry.
* PPT
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* High-resolution
e. Heterometallic coordination compounds
It has been reported that some heterometallic coordination compounds, with an
intriguing cooperative effect between the metal ions and molecule ligands, were
also a class of promising candidates for HER catalysis.109–113109. S. Li, L.
Zhang, Y. Lan, K. P. O'Halloran, H. Ma, and H. Pang, “
Polyoxometalate-encapsulated twenty-nuclear silver-tetrazole nanocage frameworks
as highly active electrocatalysts for the hydrogen evolution reaction,” Chem.
Commun. 54(16), 1964–1967 (2018). https://doi.org/10.1039/C7CC09223G110. D.
Eguchi, M. Sakamoto, and T. Teranishi, “ Ligand effect on the catalytic activity
of porphyrin-protected gold clusters in the electrochemical hydrogen evolution
reaction,” Chem. Sci. 9(1), 261–265 (2018).
https://doi.org/10.1039/C7SC03997B111. G. Hu, Z. Wu, and D-e Jiang, “
Stronger-than-Pt hydrogen adsorption in a Au22 nanocluster for the hydrogen
evolution reaction,” J. Mater. Chem. A 6(17), 7532–7537 (2018).
https://doi.org/10.1039/C8TA00461G112. N. Kuwamura, Y. Kurioka, and T. Konno, “
A platinum(ii)-palladium(ii)-nickel(ii) heterotrimetallic coordination polymer
showing a cooperative effect on catalytic hydrogen evolution,” Chem. Commun.
53(5), 846–849 (2017). https://doi.org/10.1039/C6CC08789B113. X. Gao and W.
Chen, “ Highly stable and efficient Pd6(SR)12 cluster catalysts for the hydrogen
and oxygen evolution reactions,” Chem. Commun. 53(70), 9733–9736 (2017).
https://doi.org/10.1039/C7CC04787H Li et al. constructed one polyoxometalate
(POM)-encapsulated twenty-nuclear silver-tetrazole nanocage architecture, named
as HUST-100, which exhibited a moderate H2-evolving activity with η10 = 234 mV
in 0.5 M H2SO4, arising from the combination of the porosity of metal–organic
nanocages and the redox activity of POM moieties.109109. S. Li, L. Zhang, Y.
Lan, K. P. O'Halloran, H. Ma, and H. Pang, “ Polyoxometalate-encapsulated
twenty-nuclear silver-tetrazole nanocage frameworks as highly active
electrocatalysts for the hydrogen evolution reaction,” Chem. Commun. 54(16),
1964–1967 (2018). https://doi.org/10.1039/C7CC09223G Eguchi et al.
experimentally found that the introduction of porphyrin on the Au surface
triggered charge transfer from porphyrin to the internal Au cluster, causing a
shift in the 5d state of Au that boosted hydrogen-generating behavior.110110. D.
Eguchi, M. Sakamoto, and T. Teranishi, “ Ligand effect on the catalytic activity
of porphyrin-protected gold clusters in the electrochemical hydrogen evolution
reaction,” Chem. Sci. 9(1), 261–265 (2018). https://doi.org/10.1039/C7SC03997B
At the same time, Hu et al. using first-principle calculation, predicated that
the Au22(L8)6 clusters [L8 = 1,8-bis(diphenylphosphino) octane] could be a
distinguished catalyst for the HER, even better than metallic Pt. They observed
that up to six hydrogen atoms could adsorb onto the surface of this cluster and
had a close-to-zero adsorption free energy [Figs. 12(a) and 12(b)].111111. G.
Hu, Z. Wu, and D-e Jiang, “ Stronger-than-Pt hydrogen adsorption in a Au22
nanocluster for the hydrogen evolution reaction,” J. Mater. Chem. A 6(17),
7532–7537 (2018). https://doi.org/10.1039/C8TA00461G Konno's group synthesized a
Pt2(II)–Pd2(II)–Ni(II) trimetallic coordination polymer, i.e.,
[{Ni(H2O)4}–{Pd2Pt2(NH3)4(D-pen)4}]Cl2 (D-H2pen = D-penicillamine) and explored
a cooperative effect on HER catalysis. Relative to [Pd2Pt2(NH3)4(D-pen)4]
(denoted as Pt2(II)–Pd2(II)) and trans-[Pt(NH3)2(D-pen)2]2– (denoted as Pt(II)),
a considerable augmentation in HER catalytic properties was gained in this
trimetallic coordination polymer [Fig. 12(c)], owing to containing all 10-group
metal elements.112112. N. Kuwamura, Y. Kurioka, and T. Konno, “ A
platinum(ii)-palladium(ii)-nickel(ii) heterotrimetallic coordination polymer
showing a cooperative effect on catalytic hydrogen evolution,” Chem. Commun.
53(5), 846–849 (2017). https://doi.org/10.1039/C6CC08789B Pt(II) reacted with
the PdII center to create a Pt2(II)–Pd2(II) complex, and in Pt2(II)–Pd2(II), two
NH3-based ligands could strongly bind to each Pt(II) site that exerted
non-bonding steric and NH⋯S hydrogen bonding interactions [Fig. 12(c)]. The
Pt2(II)–Pd2(II) in this Pt2(II)–Pd2(II)–Ni(II) polymer worked as an O-donating
metalloligand to the NiII center. With a stepwise combination of Pt(II) with
Pd(II) and Ni(II) centers, the electrocatalytic hydrogen evolution was greatly
improved through a heterogeneous activity, which corroborated a conspicuous
synergism because of all metal cations belonging to the same family.
FIG. 12. (a) The structures of the Au22(L8)6 cluster with different numbers of
adsorbed H. The red, yellow, blue, green, light gray, magenta, and gray balls
represent coordinatively unsaturated (cus) Au, other Au, H at cus Au, H at
non-cus Au, other H, P, and C atoms, respectively. (b) The adsorption free
energy (ΔGH) and differential adsorption energy (ΔEH) depending on the
adsorbed-H number on the surface of Au22(L8)6. Reproduced with permission from
Hu et al., J. Mater. Chem. A 6(17), 7532–7537 (2018). Copyright 2018 Royal
Society of Chemistry. (c) LSV curves of the Pt2(II)–Pd2(II)–Ni(II),
Pt2(II)–Pd2(II), and Pt(II) for the HER in a mixed solution of H2O–CH3CN. The
inset is the 1D chain heterotrimetallic structure of Pt2(II)–Pd2(II)–Ni(II).
Reproduced with permission from Kuwamura et al., Chem. Commun. 53(5), 846–849
(2017). Copyright 2017 Royal Society of Chemistry.
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3. Noble metal dopants
Noble metals, acting as dopants, could be introduced into sundry typical
catalytic materials and they have shown a huge promise for triggering new active
sites and ameliorating the intrinsically catalytic capacity of original active
centers in these materials.114–123114. M. A. Sayeed and A. P. O'Mullane, “ A
multifunctional gold doped Co(OH)2 electrocatalyst tailored for water oxidation,
oxygen reduction, hydrogen evolution and glucose detection,” J. Mater. Chem. A
5(45), 23776–23784 (2017). https://doi.org/10.1039/C7TA08928G115. S. Li, C. Xi,
Y.-Z. Jin, D. Wu, J.-Q. Wang, T. Liu, H.-B. Wang, C.-K. Dong, H. Liu, and S. A.
Kulinich, “ Ir-O-V catalytic group in Ir-doped NiV(OH)2 for overall water
splitting,” ACS Energy Lett. 4(8), 1823–1829 (2019).
https://doi.org/10.1021/acsenergylett.9b01252116. Q.-Q. Chen, C.-C. Hou, C.-J.
Wang, X. Yang, R. Shi, and Y. Chen, “ Ir4+-doped NiFe LDH to expedite hydrogen
evolution kinetics as a Pt-like electrocatalyst for water splitting,” Chem.
Commun. 54(49), 6400–6403 (2018). https://doi.org/10.1039/C8CC02872A117. G.
Chen, T. Wang, J. Zhang, P. Liu, H. Sun, X. Zhuang, M. Chen, and X. Feng, “
Accelerated hydrogen evolution kinetics on NiFe-layered double hydroxide
electrocatalysts by tailoring water dissociation active sites,” Adv. Mater.
30(10), 1706279 (2018). https://doi.org/10.1002/adma.201706279118. D. Wang, Q.
Li, C. Han, Q. Lu, Z. Xing, and X. Yang, “ Atomic and electronic modulation of
self-supported nickel-vanadium layered double hydroxide to accelerate water
splitting kinetics,” Nat. Commun. 10, 3899 (2019).
https://doi.org/10.1038/s41467-019-11765-x119. M. Qu, Y. Jiang, M. Yang, S. Liu,
Q. Guo, W. Shen, M. Li, and R. He, “ Regulating electron density of NiFe-P
nanosheets electrocatalysts by a trifle of Ru for high-efficient overall water
splitting,” Appl. Catal. B 263, 118324 (2020).
https://doi.org/10.1016/j.apcatb.2019.118324120. K.-L. Yan, X. Shang, L.-M.
Zhang, B. Dong, Z.-Z. Liu, J.-Q. Chi, W.-K. Gao, Y.-M. Chai, and C.-G. Liu, “
Boosting electrocatalytic activity of binary Ag-Fe-doped Co2P nanospheres as
bifunctional electrocatalysts for overall water splitting,” Electrochim. Acta
249(20), 16–25 (2017). https://doi.org/10.1016/j.electacta.2017.07.180121. X.
Zhang, F. Zhou, S. Zhang, Y. Liang, and R. Wang, “ Engineering MoS2 basal planes
for hydrogen evolution via synergistic ruthenium doping and nanocarbon
hybridization,” Adv. Sci. 6(10), 1900090 (2019).
https://doi.org/10.1002/advs.201900090122. J. Zhang, X. Xu, L. Yang, D. Cheng,
and D. Cao, “ Single-atom Ru doping induced phase transition of MoS2 and S
vacancy for hydrogen evolution reaction,” Small Methods 3(12), 1900653 (2019).
https://doi.org/10.1002/smtd.201900653123. Z. Luo, Y. Ouyang, H. Zhang, M. Xiao,
J. Ge, Z. Jiang, J. Wang, D. Tang, X. Cao, and C. Liu, “ Chemically activating
MoS2 via spontaneous atomic palladium interfacial doping towards efficient
hydrogen evolution,” Nat. Commun. 9, 2120 (2018).
https://doi.org/10.1038/s41467-018-04501-4 As proven cases for this strategy,
noble metal (i.e., Au, Ir, Rh, Ru, etc.)-inserted Ni/Co/Fe hydroxides were
successfully synthesized, which remarkably exceeded their pristine undoped
counterparts in HER catalysis.18,114–11718. B. Zhang, C. Zhu, Z. Wu, E.
Stavitski, Y. H. Lui, T.-H. Kim, H. Liu, L. Huang, X. Luan, and L. Zhou, “
Integrating Rh species with NiFe-layered double hydroxide for overall water
splitting,” Nano Lett. 20(1), 136–144 (2020).
https://doi.org/10.1021/acs.nanolett.9b03460114. M. A. Sayeed and A. P.
O'Mullane, “ A multifunctional gold doped Co(OH)2 electrocatalyst tailored for
water oxidation, oxygen reduction, hydrogen evolution and glucose detection,” J.
Mater. Chem. A 5(45), 23776–23784 (2017). https://doi.org/10.1039/C7TA08928G115.
S. Li, C. Xi, Y.-Z. Jin, D. Wu, J.-Q. Wang, T. Liu, H.-B. Wang, C.-K. Dong, H.
Liu, and S. A. Kulinich, “ Ir-O-V catalytic group in Ir-doped NiV(OH)2 for
overall water splitting,” ACS Energy Lett. 4(8), 1823–1829 (2019).
https://doi.org/10.1021/acsenergylett.9b01252116. Q.-Q. Chen, C.-C. Hou, C.-J.
Wang, X. Yang, R. Shi, and Y. Chen, “ Ir4+-doped NiFe LDH to expedite hydrogen
evolution kinetics as a Pt-like electrocatalyst for water splitting,” Chem.
Commun. 54(49), 6400–6403 (2018). https://doi.org/10.1039/C8CC02872A117. G.
Chen, T. Wang, J. Zhang, P. Liu, H. Sun, X. Zhuang, M. Chen, and X. Feng, “
Accelerated hydrogen evolution kinetics on NiFe-layered double hydroxide
electrocatalysts by tailoring water dissociation active sites,” Adv. Mater.
30(10), 1706279 (2018). https://doi.org/10.1002/adma.201706279 Chen et al.
claimed that the introduction of Ru dopants in the lattice of NiFe-layered
double hydroxide (NiFe-LDH) could well adjust the water-dissociation active
centers on the NiFe-LDH and subsequently improved the HER electrocatalytic
performance in base, together with remained superior OER activity.117117. G.
Chen, T. Wang, J. Zhang, P. Liu, H. Sun, X. Zhuang, M. Chen, and X. Feng, “
Accelerated hydrogen evolution kinetics on NiFe-layered double hydroxide
electrocatalysts by tailoring water dissociation active sites,” Adv. Mater.
30(10), 1706279 (2018). https://doi.org/10.1002/adma.201706279 From a similar
perspective, a handful of Rh species was also integrated with NiFe-LDH to
realize a high-efficiency bifunctional catalysis toward the OER and HER in
alkaline environments.1818. B. Zhang, C. Zhu, Z. Wu, E. Stavitski, Y. H. Lui,
T.-H. Kim, H. Liu, L. Huang, X. Luan, and L. Zhou, “ Integrating Rh species with
NiFe-layered double hydroxide for overall water splitting,” Nano Lett. 20(1),
136–144 (2020). https://doi.org/10.1021/acs.nanolett.9b03460 However, the
difference between Ru–NiFe-LDH and Rh–NiFe-LDH was due to that Rh in Rh–NiFe-LDH
existed with two states, i.e., oxidized dopants and ultrafine metallic clusters
(less than 1 nm). The doped Rh ions by replacing Fe centers worked as the
dominant OER active sites while there was a strong interaction between NiFe-LDH
and metallic Rh clusters that was responsible for the improvement of the HER. Li
and his co-workers also reported the synchronous enhancement of HER and OER
activities in the NiV LDH material by partially substituting Ni sites with Ir
atoms (NiVIr LDH) that resulted in the construction of Ir–O–V active
groups.115115. S. Li, C. Xi, Y.-Z. Jin, D. Wu, J.-Q. Wang, T. Liu, H.-B. Wang,
C.-K. Dong, H. Liu, and S. A. Kulinich, “ Ir-O-V catalytic group in Ir-doped
NiV(OH)2 for overall water splitting,” ACS Energy Lett. 4(8), 1823–1829 (2019).
https://doi.org/10.1021/acsenergylett.9b01252 The NiVIr LDH material was
prepared via employing a one-step hydrothermal route, in which Ni foam was
immersed into a mixed solution of Ni(NO3)2·6H2O, VCl3, IrCl3·xH2O, and urea, and
then the system was heated at 120 °C for 12 h. In this Ir–O–V group, the Ir atom
played multiple roles in efficient catalysis [Figs. 13(a) and 13(b)]: first, it
helped dissociate water molecules and then it tailored the charge density of
neighboring bridge O and V atoms (the charge density at O site and V site was
decreased and increased, respectively), hence simultaneously optimizing the
adsorption energies of hydrogen and oxygen intermediates, which in turn
facilitated HER and OER, respectively. The resultant NiVIr LDH achieved
outstanding catalytic properties in 1 M KOH with HER and OER overpotentials of
41 and 203 mV when sustained at 10 mA cm−2, which were 107 and 116 mV lower than
that of the pristine NiV LDH counterpart. Around the same time, Wang et al.
conducted an identical study, where Ir or Ru-doped NiV LDH (NiVIr LDH or NiVRu
LDH) were explored as HER ad OER catalysts in alkaline electrolytes, which
displayed unrivalled activity (the HER η10 of 47 and 12 mV and the OER η10 of
180 and 190 mV, respectively) and lifetime [200-h (HER) or 400-h (OER) long-term
operation at a ultrahigh current density of 200 mA cm−2 without obvious
attenuation], as obtained from Figs. 13(c) and 13(d).118118. D. Wang, Q. Li, C.
Han, Q. Lu, Z. Xing, and X. Yang, “ Atomic and electronic modulation of
self-supported nickel-vanadium layered double hydroxide to accelerate water
splitting kinetics,” Nat. Commun. 10, 3899 (2019).
https://doi.org/10.1038/s41467-019-11765-x With the assistance of the advanced
XANES and EXAFS spectroscopy methodology, the detailed electronic structure and
local atomic coordination environments were revealed to clarify the doping
effect of Ru or Ir atoms, namely, severely distorted octahedral structure at V
sites and an abundance of V vacancies were formed in the NiVIr LDH or NiVRu LDH.
When compared to the NiV LDH, the coordination number of Ni-Ni/V and V-V/Ni in
NiVIr LDH and NiVRu LDH was diminished, from 5.1 and 5.3 to 4.2/4.6 and 2.8/3.8,
respectively [Figs. 13(e) and 13(f)]. Meanwhile, there was a larger Debye–Waller
factor for the V-Ni/V after the introduction of Ir or Ru (0.0186 for NiVIr LDH
and 0.0172 for NiVRu LDH vs 0.0123 for NiV LDH), suggesting high octahedral
structure distortion. The absence of the L2 and L3 peaks in Fig. 13(g) strongly
proved that V vacancies did exist in NiVRu-LDH and NiVIr-LDH. In further
theoretical investigations, it was revealed that the energy barrier of each
elementary step for the HER and OER was reduced after Ru or Ir doping,
particularly noting Ru for HER and Ir for OER. Hence, together with this
optimized reaction energy of each step, the electronic and atomic modulation of
NiV LDH contributed to the favorable HER and OER catalysis.
FIG. 13. Active sites (top) and charge density distribution (down) for the
overall water splitting of the (a) NiV LDH and (b) NiVIr LDH samples. Reproduced
with permission from Li et al., ACS Energy Lett. 4(8), 1823–1829 (2019).
Copyright 2019 American Chemical Society. LSV curves for (c) HER and (d) OER in
various samples of NiV LDH, NiVIr LDH, NiVRu LDH, bare Ni foam, and the
benchmark catalysts, i.e., Pt/C (for HER) and RuO2 (for OER). The extended XANES
oscillation functions of (e) Ni K-edge and (f) V K-edge. (g) XANES spectra of
the V L-edge and O K-edge. Reproduced with permission from Wang et al., Nat.
Commun. 10, 3899 (2019). Copyright 2019 Nature Publishing Group.
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Following the manifested positive effect of noble metal dopant on hydroxides,
several optimization researches in the metal phosphides have also been
performed.119,120119. M. Qu, Y. Jiang, M. Yang, S. Liu, Q. Guo, W. Shen, M. Li,
and R. He, “ Regulating electron density of NiFe-P nanosheets electrocatalysts
by a trifle of Ru for high-efficient overall water splitting,” Appl. Catal. B
263, 118324 (2020). https://doi.org/10.1016/j.apcatb.2019.118324120. K.-L. Yan,
X. Shang, L.-M. Zhang, B. Dong, Z.-Z. Liu, J.-Q. Chi, W.-K. Gao, Y.-M. Chai, and
C.-G. Liu, “ Boosting electrocatalytic activity of binary Ag-Fe-doped Co2P
nanospheres as bifunctional electrocatalysts for overall water splitting,”
Electrochim. Acta 249(20), 16–25 (2017).
https://doi.org/10.1016/j.electacta.2017.07.180 Qu et al. replaced a small
fraction of catalytic Ni sites in the NiFe phosphide (NiFe–P) by Ru atoms and
evaluated their influence on the HER catalytic behavior.119119. M. Qu, Y. Jiang,
M. Yang, S. Liu, Q. Guo, W. Shen, M. Li, and R. He, “ Regulating electron
density of NiFe-P nanosheets electrocatalysts by a trifle of Ru for
high-efficient overall water splitting,” Appl. Catal. B 263, 118324 (2020).
https://doi.org/10.1016/j.apcatb.2019.118324 The addition of Ru reduced the H
adsorption free energies on original P sites and raised additional active sites
on Ru atoms, simultaneously accompanied by the optimization of the electronic
properties with heightened conductivity. Thus, Ru-incorporated NiFe–P speed up
the HER dynamics in 1 M KOH, which only needed 44 mV overpotential to drive a 10
mA cm−2 current density and displayed a small Tafel slope of 80 mV dec−1.
Additionally, prior to this study, Yan et al. underscored the role of Ag dopants
on the HER activity of Ru-incorporated Fe–Co2P. The enhanced conductivity and
electron-donating ability from Ag doping accounted for the amelioration of the
HER activities.120120. K.-L. Yan, X. Shang, L.-M. Zhang, B. Dong, Z.-Z. Liu,
J.-Q. Chi, W.-K. Gao, Y.-M. Chai, and C.-G. Liu, “ Boosting electrocatalytic
activity of binary Ag-Fe-doped Co2P nanospheres as bifunctional electrocatalysts
for overall water splitting,” Electrochim. Acta 249(20), 16–25 (2017).
https://doi.org/10.1016/j.electacta.2017.07.180
Another sort of host materials for noble-metal doping are 2D layered metal
chalcogenides, especially the classical MoS2 with the stable 2H phase, in which
the edge S atoms are generally deemed as active sites toward hydrogen
evolution.121–124121. X. Zhang, F. Zhou, S. Zhang, Y. Liang, and R. Wang, “
Engineering MoS2 basal planes for hydrogen evolution via synergistic ruthenium
doping and nanocarbon hybridization,” Adv. Sci. 6(10), 1900090 (2019).
https://doi.org/10.1002/advs.201900090122. J. Zhang, X. Xu, L. Yang, D. Cheng,
and D. Cao, “ Single-atom Ru doping induced phase transition of MoS2 and S
vacancy for hydrogen evolution reaction,” Small Methods 3(12), 1900653 (2019).
https://doi.org/10.1002/smtd.201900653123. Z. Luo, Y. Ouyang, H. Zhang, M. Xiao,
J. Ge, Z. Jiang, J. Wang, D. Tang, X. Cao, and C. Liu, “ Chemically activating
MoS2 via spontaneous atomic palladium interfacial doping towards efficient
hydrogen evolution,” Nat. Commun. 9, 2120 (2018).
https://doi.org/10.1038/s41467-018-04501-4124. K. Vasu, O. E. Meiron, A. N.
Enyashin, R. Bar-Ziv, and M. Bar-Sadan, “ Effect of Ru doping on the properties
of MoSe2 nanoflowers,” J. Phys. Chem. C 123(3), 1987–1994 (2019).
https://doi.org/10.1021/acs.jpcc.8b11712 The introduction of Ru atoms in 2H-MoS2
has been successfully reported to upgrade the HER catalytic performance. Wang's
group utilized the systematic experimental and theoretical tools to give a
reasonable explanation for this performance enhancement. The in-plane S atoms
adjacent to Ru atoms turned into new active centers, which further not only
substantially accelerated water adsorption and dissociation, but also favored
hydrogen adsorption/desorption.121121. X. Zhang, F. Zhou, S. Zhang, Y. Liang,
and R. Wang, “ Engineering MoS2 basal planes for hydrogen evolution via
synergistic ruthenium doping and nanocarbon hybridization,” Adv. Sci. 6(10),
1900090 (2019). https://doi.org/10.1002/advs.201900090 Noteworthily, it was
widely accepted that metastable 1T-MoS2 with basal-plane S atoms as active
centers was more conductive and catalytically active for the HER than 2H-MoS2.
In a recent published work proposed by Zhang et al., a phase transition from 2H
to 1T and rich S vacancies induced by single-atom Ru doping for concurrently
decreasing the energy barrier of water-dissociation and hydrogen-adsorption
steps was believed to be the essential origin of phenomenal activity for the HER
in MoS2 [Figs. 14(b) and 14(c)].122122. J. Zhang, X. Xu, L. Yang, D. Cheng, and
D. Cao, “ Single-atom Ru doping induced phase transition of MoS2 and S vacancy
for hydrogen evolution reaction,” Small Methods 3(12), 1900653 (2019).
https://doi.org/10.1002/smtd.201900653 The MoS2 inserted with Ru single atoms
(denoted as SA-Ru-MoS2) was obtained by simple adding and stirring of MoS2
nanosheets in a RuCl3 solution, along with subsequent vacuum drying [Fig.
14(a)]. Energy dispersive spectrometer (EDS) quantitative analysis unveiled an
atomic ratio of 1:1.64 for Mo and S, suggesting the presence of plentiful S
vacancies (Sv). A dark-field scanning TEM image of the SA–Ru–MoS2 sample, shown
in Fig. 14(b), exhibited visibly distinguished structural regions, where Mo and
S atoms were represented by red and green spheres, respectively. The common
honeycomb lattice framework corresponded to a 2H-MoS2 phase while the trigonal
lattice region referred to 1T-MoS2 structure. Toward hydrogen production in
basic electrolytes, the current density of 10 mA cm−2 was reached at the
overpotential of 76 mV for the best SA–Ru–MoS2 sample, which approached to Pt/C
(51 mV). Correspondingly, DFT results confirmed that at the 1T-Ru-MoS2-Sv site,
a spontaneous water dissociation occurred and the adsorption/desorption energy
of Hads species was much closer to ideal value, i.e., 0 [Fig. 14(c)]. This
finding was also in good agreement with a previous study by Xing's group, in
which the Mo sites in MoS2 were substituted with trace amounts of Pd (only 1 wt.
% of Pd).123123. Z. Luo, Y. Ouyang, H. Zhang, M. Xiao, J. Ge, Z. Jiang, J. Wang,
D. Tang, X. Cao, and C. Liu, “ Chemically activating MoS2 via spontaneous atomic
palladium interfacial doping towards efficient hydrogen evolution,” Nat. Commun.
9, 2120 (2018). https://doi.org/10.1038/s41467-018-04501-4 The resultant
Pd-doped MoS2 afforded the overpotential of 78 mV at 10 mA cm−2 and an 805 μA
cm−2 exchange current density, as well as a good matrix stability. Impressively,
Wang et al. and Huang et al. uncovered that the doping of a small quantity of Pd
could powerfully activate this otherwise non-electroactive TaS2 and NbS2 as
highly excellent HER electrocatalysts.125,126125. C. Huang, X. Wang, D. Wang, W.
Zhao, K. Bu, J. Xu, X. Huang, Q. Bi, J. Huang, and F. Huang, “ Atomic pillar
effect in PdxNbS2 to boost basal plane activity for stable hydrogen evolution,”
Chem. Mater. 31(13), 4726–4731 (2019).
https://doi.org/10.1021/acs.chemmater.9b00821126. D. Wang, X. Wang, Y. Lu, C.
Song, J. Pan, C. Li, M. Sui, W. Zhao, and F. Huang, “ Atom-scale dispersed
palladium in a conductive Pd0.1TaS2 lattice with a unique electronic structure
for efficient hydrogen evolution,” J. Mater. Chem. A 5(43), 22618–22624 (2017).
https://doi.org/10.1039/C7TA06447K
FIG. 14. (a) The schematic synthesis pathway of SA–Ru–MoS2. (b) A dark-field
scanning TEM image of the SA–Ru–MoS2 sample. (c) Free energy diagrams toward the
alkaline HER in different MoS2 active sites. Reproduced with permission from
Zhang et al., Small Methods 3(12), 1900653 (2019). Copyright 2019 Wiley-VCH.
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Table I summarizes the HER performance in the different media for various
representative non-Pt NMN electrocatalysts with different element compositions.
TABLE I. Performance of various representative non-Pt NMN HER electrocatalysts
with different element compositions.
Catalyst Electrolyte Loading (mg cm−2) Overpotential η10 (mV) Tafel slope (mV
dec−1) Stability References Ir6Ag9 NTs 0.5 M H2SO4 13.3 μgIr cm−2 20 27.5 −5 mA
cm−2 @ 5 h 3434. M. Zhu, Q. Shao, Y. Qian, and X. Huang, “ Superior overall
water splitting electrocatalysis in acidic conditions enabled by bimetallic
Ir-Ag nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.023 Pd66Ag17Al17 1 M KOH … 16.8 56
10 000 CV 3535. R.-Q. Yao, Y.-T. Zhou, H. Shi, Q.-H. Zhang, L. Gu, Z. Wen, X.-Y.
Lang, and Q. Jiang, “ Nanoporous palladium-silver surface alloys as efficient
and pH-universal catalysts for the hydrogen evolution reaction,” ACS Energy
Lett. 4(6), 1379–1386 (2019). https://doi.org/10.1021/acsenergylett.9b00845 0.5
M H2SO4 … ∼35 26 30 000 CV Pd3Ru 1 M KOH 0.015 42 … … 3939. X. Qin, L. Zhang,
G.-L. Xu, S. Zhu, Q. Wang, M. Gu, X. Zhang, C. Sun, P. B. Balbuena, and K.
Amine, “ The role of Ru in improving the activity of Pd toward hydrogen
evolution and oxidation reactions in alkaline solutions,” ACS Catal. 9(10),
9614–9621 (2019). https://doi.org/10.1021/acscatal.9b01744 Pd/Cu-Pt NRs 0.5 M
H2SO4 0.040 22.8 25 5000 CV or −24 mV @ 15 h 4141. T. Chao, X. Luo, W. Chen, B.
Jiang, J. Ge, Y. Lin, G. Wu, X. Wang, Y. Hu, and Z. Zhuang, “ Atomically
dispersed copper-platinum dual sites alloyed with palladium nanorings catalyze
the hydrogen evolution reaction,” Angew. Chem., Int. Ed. 129(50), 16263–16267
(2017). https://doi.org/10.1002/ange.201709803 PtRu 0.5 M H2SO4 13.9 μgRu cm−2 8
25 10 000 CV or −15/40/30 mV @ 10 h 4444. L. Li, G. Zhang, B. Wang, T. Yang, and
S. Yang, “ Electrochemical formation of PtRu bimetallic nanoparticles for highly
efficient and pH-universal hydrogen evolution reaction,” J. Mater. Chem. A 8(4),
2090–2098 (2020). https://doi.org/10.1039/C9TA12300H 1 M PBS 25 36 1 M KOH 19 28
PtRu@RFCS-6h 0.5 M H2SO4 0.354 19.7 27.2 5000 CV or −10 mA cm−2 @ 48 h 4343. K.
Li, Y. Li, Y. Wang, J. Ge, C. Liu, and W. Xing, “ Enhanced electrocatalytic
performance for the hydrogen evolution reaction through surface enrichment of
platinum nanoclusters alloying with ruthenium in situ embedded in carbon,”
Energy Environ. Sci. 11(5), 1232–1239 (2018). https://doi.org/10.1039/C8EE00402A
RuAu-0.2 1 M KOH 0.056 24 37 1000 CV or −10 mA cm−2 @ 10 h 4646. C. H. Chen, D.
Wu, Z. Li, R. Zhang, C. G. Kuai, X. R. Zhao, C. K. Dong, S. Z. Qiao, H. Liu, and
X. W. Du, “ Ruthenium-based single-atom alloy with high electrocatalytic
activity for hydrogen evolution,” Adv. Energy Mater. 9(20), 1803913 (2019).
https://doi.org/10.1002/aenm.201803913 IrNi NCs 0.1 M HClO4 12.5 μgIr cm−2 19
(η20) … −5 mA cm−2 @ 2 h 5050. Y. Pi, Q. Shao, P. Wang, J. Guo, and X. Huang, “
General formation of monodisperse IrM (M = Ni, Co, Fe) bimetallic nanoclusters
as bifunctional electrocatalysts for acidic overall water splitting,” Adv.
Funct. Mater. 27(27), 1700886 (2017). https://doi.org/10.1002/adfm.201700886
IrNi NFs 0.1 M HClO4 7.8 μgIr cm−2 25 29.7 1000 CV or −10 mA cm−2 @ 6 h 5151. F.
Lv, W. Zhang, W. Yang, J. Feng, K. Wang, J. Zhou, P. Zhou, and S. Guo, “
Ir-based alloy nanoflowers with optimized hydrogen binding energy as
bifunctional electrocatalysts for overall water splitting,” Small Methods 4(6),
1900129 (2020). https://doi.org/10.1002/smtd.201900129 AgNi-5 1 M KOH 1.32 24 61
−150 mV @ 5d 5454. R. Majee, A. Kumar, T. Das, S. Chakraborty, and S.
Bhattacharyya, “ Tweaking nickel with minimal silver in a heterogeneous alloy of
decahedral geometry to deliver platinum-like hydrogen evolution activity,”
Angew. Chem., Int. Ed. 59(7), 2881–2889 (2020).
https://doi.org/10.1002/anie.201913704 Au-Cu/CNFs-1:2 0.5 M H2SO4 … 83 70 −0.136
V @ 24 h 6060. J. Wang, H. Zhu, D. Yu, J. Chen, J. Chen, M. Zhang, L. Wang, and
M. Du, “ Engineering the composition and structure of bimetallic Au-Cu alloy
nanoparticles in carbon nanofibers: Self-supported electrode materials for
electrocatalytic water splitting,” ACS Appl. Mater. Interfaces 9(23),
19756–19765 (2017). https://doi.org/10.1021/acsami.7b01418 np-Cu53Ru47 1 M KOH
0.306 15 30 −15 mV @ 27 h 6161. Q. Wu, M. Luo, J. Han, W. Peng, Y. Zhao, D.
Chen, M. Peng, J. Liu, F. M. de Groot, and Y. Tan, “ Identifying
electrocatalytic sites of the nanoporous copper-ruthenium alloy for hydrogen
evolution reaction in alkaline electrolyte,” ACS Energy Lett. 5(1), 192–199
(2020). https://doi.org/10.1021/acsenergylett.9b02374 1 M PBS 41 35 −40 mV @ 27
h IrW ND 0.1 M HClO4 10.2 μgIr cm−2 12 … 1000 CV 6262. F. Lv, J. Feng, K. Wang,
Z. Dou, W. Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “
Iridium-tungsten alloy nanodendrites as pH-universal water-splitting
electrocatalysts,” ACS Cent. Sci. 4(9), 1244–1252 (2018).
https://doi.org/10.1021/acscentsci.8b00426 0.1 M KOH 29 … IrNiTa MG nanofilm 0.5
M H2SO4 8.14 μgIr cm−2 99 35 1000 CV or −10 mA cm−2 @ 10 h 6565. Z. J. Wang, M.
X. Li, J. H. Yu, X. B. Ge, Y. H. Liu, and W. H. Wang, “ Low-iridium-content
IrNiTa metallic glass films as intrinsically active catalysts for hydrogen
evolution reaction,” Adv. Mater. 32(4), 1906384 (2020).
https://doi.org/10.1002/adma.201906384 Co-RuIr 0.1 M HClO4 0.051 14 31.1 −10 mA
cm−2 @ 25 h 6767. J. Shan, T. Ling, K. Davey, Y. Zheng, and S. Z. Qiao, “
Transition-metal-doped RuIr bifunctional nanocrystals for overall water
splitting in acidic environments,” Adv. Mater. 31(17), 1900510 (2019).
https://doi.org/10.1002/adma.201900510 Ru38Pd34Ni28 NSs 1 M KOH 20 65 10 000 CV
6868. D. Zhang, H. Zhao, B. Huang, B. Li, H. Li, Y. Han, Z. Wang, X. Wu, Y. Pan,
and Y. Sun, “ Advanced ultrathin RuPdM (M = Ni, Co, Fe) nanosheets
electrocatalyst boosts hydrogen evolution,” ACS Cent. Sci. 5(12), 1991–1997
(2019). https://doi.org/10.1021/acscentsci.9b01110 RuIrOx 0.5 M H2SO4 0.833 12
21 3000 CV 6969. Z. Zhuang, Y. Wang, C.-Q. Xu, S. Liu, C. Chen, Q. Peng, Z.
Zhuang, H. Xiao, Y. Pan, and S. Lu, “ Three-dimensional open nano-netcage
electrocatalysts for efficient pH-universal overall water splitting,” Nat.
Commun. 10, 4875 (2019). https://doi.org/10.1038/s41467-019-12885-0 1 M KOH 13
23 w-Rh2P NS 0.1 M HClO4 0.0123 15.8 29.9 1000 CV 8484. K. Wang, B. Huang, F.
Lin, F. Lv, M. Luo, P. Zhou, Q. Liu, W. Zhang, C. Yang, and Y. Tang, “ Wrinkled
Rh2P nanosheets as superior pH-universal electrocatalysts for hydrogen evolution
catalysis,” Adv. Energy Mater. 8(27), 1801891 (2018).
https://doi.org/10.1002/aenm.201801891 0.1 M PBS 21.9 78.4 0.1 M KOH 18.3 61.5
L-RuP 0.5 M H2SO4 0.185 19 37 −10 mA cm−2 @ 200 h 8787. J. Yu, Y. Guo, S. She,
S. Miao, M. Ni, W. Zhou, M. Liu, and Z. Shao, “ Bigger is surprisingly better:
Agglomerates of larger RuP nanoparticles outperform benchmark Pt nanocatalysts
for the hydrogen evolution reaction,” Adv. Mater. 30(39), 1800047 (2018).
https://doi.org/10.1002/adma.201800047 1 M PBS 95 54 1 M KOH 18 34 PdP2@CB 0.5 M
H2SO4 0.285 27.5 29.5 5000 CV or −27.5/84.6/35.4 mV @ 10 h 9292. F. Luo, Q.
Zhang, X. Yu, S. Xiao, Y. Ling, H. Hu, L. Guo, Z. Yang, L. Huang, and W. Cai, “
Palladium phosphide as a stable and efficient electrocatalyst for overall water
splitting,” Angew. Chem., Int. Ed. 57(45), 14862–14867 (2018).
https://doi.org/10.1002/anie.201810102 1 M PBS 84.6 72.3 1 M KOH 35.4 42.1
IrP2@NC 0.5 M H2SO4 0.7 8 28 1000 CV 9191. Z. Pu, J. Zhao, I. S. Amiinu, W. Li,
M. Wang, D. He, and S. Mu, “ A universal synthesis strategy for P-rich noble
metal diphosphide-based electrocatalysts for the hydrogen evolution reaction,”
Energy Environ. Sci. 12(3), 952–957 (2019). https://doi.org/10.1039/C9EE00197B 1
M KOH 28 50 RuS2-500 1 M KOH 0.278 78 ∼40 1000 CV 100100. Y. Zhu, H. A. Tahini,
Y. Wang, Q. Lin, Y. Liang, C. M. Doherty, Y. Liu, X. Li, J. Lu, and S. C. Smith,
“ Pyrite-type ruthenium disulfide with tunable disorder and defects enables
ultra-efficient overall water splitting,” J. Mater. Chem. A 7(23), 14222–14232
(2019). https://doi.org/10.1039/C9TA04120F Hollow hexagonal Rh2S3 0.5 M H2SO4
0.153 122 44 10 000 CV 9595. D. Yoon, B. Seo, J. Lee, K. S. Nam, B. Kim, S.
Park, H. Baik, S. H. Joo, and K. Lee, “ Facet-controlled hollow Rh2S3 hexagonal
nanoprisms as highly active and structurally robust catalysts toward hydrogen
evolution reaction,” Energy Environ. Sci. 9(3), 850–856 (2016).
https://doi.org/10.1039/C5EE03456F Li-IrSe2 0.5 M H2SO4 0.25 55 … −64/173/105 mV
@ 10 h 9999. T. Zheng, C. Shang, Z. He, X. Wang, C. Cao, H. Li, R. Si, B. Pan,
S. Zhou, and J. Zeng, “ Intercalated iridium diselenide electrocatalysts for
efficient pH-universal water splitting,” Angew. Chem., Int. Ed. 131(41),
14906–14911 (2019). https://doi.org/10.1002/ange.201909369 1 M PBS 120 … 1 M KOH
72 … Li-PPS 0.5 M H2SO4 0.282 52 29 10 000 CV or −20 mA cm−2 @ 12 h 103103. X.
Zhang, Z. Luo, P. Yu, Y. Cai, Y. Du, D. Wu, S. Gao, C. Tan, Z. Li, and M. Ren, “
Lithiation-induced amorphization of Pd3P2S8 for highly efficient hydrogen
evolution,” Nat. Catal. 1(6), 460–468 (2018).
https://doi.org/10.1038/s41929-018-0072-y Pd2B NS 0.5 M H2SO4 … 15.3 22.5 1000
CV or initial −10 mA cm−2 @ 12 h 104104. L. Chen, L.-R. Zhang, L.-Y. Yao, Y.-H.
Fang, L. He, G.-F. Wei, and Z.-P. Liu, “ Metal boride better than Pt: HCP Pd2B
as a superactive hydrogen evolution reaction catalyst,” Energy Environ. Sci.
12(10), 3099–3105 (2019). https://doi.org/10.1039/C9EE01564G RuSi 0.5 M H2SO4
0.562 19 28.9 … 106106. H. Chen, X. Ai, W. Liu, Z. Xie, W. Feng, W. Chen, and X.
Zou, “ Promoting subordinate, efficient ruthenium sites with interstitial
silicon for Pt-like electrocatalytic activity,” Angew. Chem., Int. Ed. 58(33),
11409–11413 (2019). https://doi.org/10.1002/anie.201906394 Rh2C 1 M KOH … 13
(η5) 74.5 1000 CV or −5 mA cm−2 @ 10 h 7373. T. Wakisaka, K. Kusada, D. Wu, T.
Yamamoto, T. Toriyama, S. Matsumura, H. Akiba, O. Yamamuro, K. Ikeda, and T.
Otomo, “ Rational synthesis for a noble metal carbide,” J. Am. Chem. Soc.
142(3), 1247–1253 (2020). https://doi.org/10.1021/jacs.9b09219 HUST-100 0.5 M
H2SO4 … 234 82 2000 CV 109109. S. Li, L. Zhang, Y. Lan, K. P. O'Halloran, H. Ma,
and H. Pang, “ Polyoxometalate-encapsulated twenty-nuclear silver-tetrazole
nanocage frameworks as highly active electrocatalysts for the hydrogen evolution
reaction,” Chem. Commun. 54(16), 1964–1967 (2018).
https://doi.org/10.1039/C7CC09223G Rh-NiFe-LDH 1 M KOH 10.2 μgRh cm−2 57 81.3
1000 CV 1818. B. Zhang, C. Zhu, Z. Wu, E. Stavitski, Y. H. Lui, T.-H. Kim, H.
Liu, L. Huang, X. Luan, and L. Zhou, “ Integrating Rh species with NiFe-layered
double hydroxide for overall water splitting,” Nano Lett. 20(1), 136–144 (2020).
https://doi.org/10.1021/acs.nanolett.9b03460 NiVIr LDH 1 M KOH 1.7 41 mV 55.3
2000 CV or −10 mA cm−2 @ 10 h 115115. S. Li, C. Xi, Y.-Z. Jin, D. Wu, J.-Q.
Wang, T. Liu, H.-B. Wang, C.-K. Dong, H. Liu, and S. A. Kulinich, “ Ir-O-V
catalytic group in Ir-doped NiV(OH)2 for overall water splitting,” ACS Energy
Lett. 4(8), 1823–1829 (2019). https://doi.org/10.1021/acsenergylett.9b01252
NiVRu LDH 1 M KOH 1.2 12 40 2000 CV or −50/200 mA cm−2 @ 200h 118118. D. Wang,
Q. Li, C. Han, Q. Lu, Z. Xing, and X. Yang, “ Atomic and electronic modulation
of self-supported nickel-vanadium layered double hydroxide to accelerate water
splitting kinetics,” Nat. Commun. 10, 3899 (2019).
https://doi.org/10.1038/s41467-019-11765-x Ru–NiFe–P 1 M KOH … 44 80 1000 CV
119119. M. Qu, Y. Jiang, M. Yang, S. Liu, Q. Guo, W. Shen, M. Li, and R. He, “
Regulating electron density of NiFe-P nanosheets electrocatalysts by a trifle of
Ru for high-efficient overall water splitting,” Appl. Catal. B 263, 118324
(2020). https://doi.org/10.1016/j.apcatb.2019.118324 SA–Ru–MoS2 1 M KOH 0.285 76
21 … 122122. J. Zhang, X. Xu, L. Yang, D. Cheng, and D. Cao, “ Single-atom Ru
doping induced phase transition of MoS2 and S vacancy for hydrogen evolution
reaction,” Small Methods 3(12), 1900653 (2019).
https://doi.org/10.1002/smtd.201900653 Pd-MoS2 0.5 M H2SO4 0.222 78 62 5000 CV
or −10 mA cm−2 @ 100 h 123123. Z. Luo, Y. Ouyang, H. Zhang, M. Xiao, J. Ge, Z.
Jiang, J. Wang, D. Tang, X. Cao, and C. Liu, “ Chemically activating MoS2 via
spontaneous atomic palladium interfacial doping towards efficient hydrogen
evolution,” Nat. Commun. 9, 2120 (2018).
https://doi.org/10.1038/s41467-018-04501-4
B. Size control and morphological tuning
Modulating the size and shape of noble-metal nanocrystals with high surface area
can efficiently improve the atomic utilization and expose more active centers,
resulting in a gain in the HER catalytic activity.20,74,127–14120. J. Wang, Z.
Wei, S. Mao, H. Li, and Y. Wang, “ Highly uniform Ru nanoparticles over N-doped
carbon: pH and temperature-universal hydrogen release from water reduction,”
Energy Environ. Sci. 11(4), 800–806 (2018).
https://doi.org/10.1039/C7EE03345A74. J. Ahmed and Y. Mao, “ Ultrafine iridium
oxide nanorods synthesized by molten salt method toward electrocatalytic oxygen
and hydrogen evolution reactions,” Electrochim. Acta 212(10), 686–693 (2016).
https://doi.org/10.1016/j.electacta.2016.06.122127. Q. Wang, M. Ming, S. Niu, Y.
Zhang, G. Fan, and J. S. Hu, “ Scalable solid-state synthesis of highly
dispersed uncapped metal (Rh, Ru, Ir) nanoparticles for efficient hydrogen
evolution,” Adv. Energy Mater. 8(31), 1801698 (2018).
https://doi.org/10.1002/aenm.201801698128. M. Ming, Y. Zhang, C. He, L. Zhao, S.
Niu, G. Fan, and J. S. Hu, “ Room-temperature sustainable synthesis of selected
platinum group metal (PGM = Ir, Rh, and Ru) nanocatalysts well-dispersed on
porous carbon for efficient hydrogen evolution and oxidation,” Small 15(49),
1903057 (2019). https://doi.org/10.1002/smll.201903057129. B. K. Barman, D. Das,
and K. K. Nanda, “ Facile synthesis of ultrafine Ru nanocrystal supported
N-doped graphene as an exceptional hydrogen evolution electrocatalyst in both
alkaline and acidic media,” Sustainable Energy Fuels 1(5), 1028–1033 (2017).
https://doi.org/10.1039/C7SE00153C130. Y. Wang, Y. Sun, H. Liao, S. Sun, S. Li,
J. W. Ager, and Z. J. Xu, “ Activation effect of electrochemical cycling on gold
nanoparticles towards the hydrogen evolution reaction in sulfuric acid,”
Electrochim. Acta 209(10), 440–447 (2016).
https://doi.org/10.1016/j.electacta.2016.05.095131. K. A. Kuttiyiel, K. Sasaki,
W.-F. Chen, D. Su, and R. R. Adzic, “ Core-shell, hollow-structured
iridium-nickel nitride nanoparticles for the hydrogen evolution reaction,” J.
Mater. Chem. A 2(3), 591–594 (2014). https://doi.org/10.1039/C3TA14301E132. T.
D. Tran, M. T. Nguyen, H. V. Le, D. N. Nguyen, Q. D. Truong, and P. D. Tran, “
Gold nanoparticles as an outstanding catalyst for the hydrogen evolution
reaction,” Chem. Commun. 54(27), 3363–3366 (2018).
https://doi.org/10.1039/C8CC00038G133. J. Zheng, S. Zhou, S. Gu, B. Xu, and Y.
Yan, “ Size-dependent hydrogen oxidation and evolution activities on supported
palladium nanoparticles in acid and base,” J. Electrochem. Soc. 163(6), F499
(2016). https://doi.org/10.1149/2.0661606jes134. J. Li, P. Zhou, F. Li, J. Ma,
Y. Liu, X. Zhang, H. Huo, J. Jin, and J. Ma, “ Shape-controlled synthesis of Pd
polyhedron supported on polyethyleneimine-reduced graphene oxide for enhancing
the efficiency of hydrogen evolution reaction,” J. Power Sources 302(20),
343–351 (2016). https://doi.org/10.1016/j.jpowsour.2015.10.050135. T.-R. Kuo,
Y.-C. Lee, H.-L. Chou, M. G. Swathi, C.-Y. Wei, C.-Y. Wen, Y.-H. Chang, X.-Y.
Pan, and D.-Y. Wang, “ Plasmon-enhanced hydrogen evolution on specific facet of
silver nanocrystals,” Chem. Mater. 31(10), 3722–3728 (2019).
https://doi.org/10.1021/acs.chemmater.9b00652136. J. Yang, Y. Ji, Q. Shao, N.
Zhang, Y. Li, and X. Huang, “ A universal strategy to metal wavy nanowires for
efficient electrochemical water splitting at pH-universal conditions,” Adv.
Funct. Mater. 28(41), 1803722 (2018). https://doi.org/10.1002/adfm.201803722137.
C. Zhang, S. Liu, Z. Mao, X. Liang, and B. Chen, “ Ag-Ni core-shell nanowires
with superior electrocatalytic activity for alkaline hydrogen evolution
reaction,” J. Mater. Chem. A 5(32), 16646–16652 (2017).
https://doi.org/10.1039/C7TA04220E138. L. Fu, F. Yang, G. Cheng, and W. Luo, “
Ultrathin Ir nanowires as high-performance electrocatalysts for efficient water
splitting in acidic media,” Nanoscale 10(4), 1892–1897 (2018).
https://doi.org/10.1039/C7NR09377B139. L. Zhang, L. Liu, H. Wang, H. Shen, Q.
Cheng, C. Yan, and S. Park, “ Electrodeposition of rhodium nanowires arrays and
their morphology-dependent hydrogen evolution activity,” Nanomaterials 7(5), 103
(2017). https://doi.org/10.3390/nano7050103140. Q. Lu, A. L. Wang, H. Cheng, Y.
Gong, Q. Yun, N. Yang, B. Li, B. Chen, Q. Zhang, and Y. Zong, “ Synthesis of
hierarchical 4H/fcc Ru nanotubes for highly efficient hydrogen evolution in
alkaline media,” Small 14(30), 1801090 (2018).
https://doi.org/10.1002/smll.201801090141. R. Nazir, U. Basak, and S. Pande, “
Synthesis of one-dimensional RuO2 nanorod for hydrogen and oxygen evolution
reaction: An efficient and stable electrocatalyst,” Colloids Surf. A 560(5),
141–148 (2019). https://doi.org/10.1016/j.colsurfa.2018.10.009 In this regard,
the ultrafine nanoparticle is the most common nanostructure. Generally, the
nanoparticles could be fabricated by in situ growth or low-temperature reduction
on various supports.20,127,12820. J. Wang, Z. Wei, S. Mao, H. Li, and Y. Wang, “
Highly uniform Ru nanoparticles over N-doped carbon: pH and
temperature-universal hydrogen release from water reduction,” Energy Environ.
Sci. 11(4), 800–806 (2018). https://doi.org/10.1039/C7EE03345A127. Q. Wang, M.
Ming, S. Niu, Y. Zhang, G. Fan, and J. S. Hu, “ Scalable solid-state synthesis
of highly dispersed uncapped metal (Rh, Ru, Ir) nanoparticles for efficient
hydrogen evolution,” Adv. Energy Mater. 8(31), 1801698 (2018).
https://doi.org/10.1002/aenm.201801698128. M. Ming, Y. Zhang, C. He, L. Zhao, S.
Niu, G. Fan, and J. S. Hu, “ Room-temperature sustainable synthesis of selected
platinum group metal (PGM = Ir, Rh, and Ru) nanocatalysts well-dispersed on
porous carbon for efficient hydrogen evolution and oxidation,” Small 15(49),
1903057 (2019). https://doi.org/10.1002/smll.201903057 One kind of typical cases
is to carbonize metal salt/organic molecule precursors that are tailorable in
nanostructure and composition.20,12920. J. Wang, Z. Wei, S. Mao, H. Li, and Y.
Wang, “ Highly uniform Ru nanoparticles over N-doped carbon: pH and
temperature-universal hydrogen release from water reduction,” Energy Environ.
Sci. 11(4), 800–806 (2018). https://doi.org/10.1039/C7EE03345A129. B. K. Barman,
D. Das, and K. K. Nanda, “ Facile synthesis of ultrafine Ru nanocrystal
supported N-doped graphene as an exceptional hydrogen evolution electrocatalyst
in both alkaline and acidic media,” Sustainable Energy Fuels 1(5), 1028–1033
(2017). https://doi.org/10.1039/C7SE00153C In this study from Nanda's group, a
composite of ultrafine Ru nanocrystals loaded on N-doped graphene (Ru@NG-x) was
prepared by employing dicyanamide (DCA) and RuCl3 as the carbon precursor and
metal source, respectively, and its micro-morphology was effectively manipulated
by the mass ratio of these raw materials (x).129129. B. K. Barman, D. Das, and
K. K. Nanda, “ Facile synthesis of ultrafine Ru nanocrystal supported N-doped
graphene as an exceptional hydrogen evolution electrocatalyst in both alkaline
and acidic media,” Sustainable Energy Fuels 1(5), 1028–1033 (2017).
https://doi.org/10.1039/C7SE00153C The high-resolution TEM (HRTEM) images
revealed that when x was equal to 2 or 4, the Ru nanocrystals in the Ru@NG
samples had the average size of ∼2 nm, while increasing x to 10 could cause a
double increment in the diameter of Ru nanocrystals, approximately 4–5 nm.
Through the electrochemical experiments in both acidic and alkaline
electrolytes, it was confirmed that the catalytic activity for HER in the three
samples (i.e., Ru@NG-2, Ru@NG-4, and Ru@NG-10) followed a sequence of Ru@NG-2 ≈
Ru@NG-4 > Ru@NG-10, which was inversely in accordance with the trend of the Ru
nanocrystal size: Ru@NG-2 ≈ Ru@NG-4 (∼2 nm) < Ru@NG-10 (4–5 nm). Further summary
or analysis about this part is presented in Sec. IV C. Facile solvothermal
synthesis was also developed to generate well-dispersed nanoparticles in the
absence of supports. For example, Fu et al. designed monodispersed IrNiFe
nanoparticles (NPs) with a mean size of 2.2 nm.6464. L. Fu, G. Cheng, and W.
Luo, “ Colloidal synthesis of monodisperse trimetallic IrNiFe nanoparticles as
highly active bifunctional electrocatalysts for acidic overall water splitting,”
J. Mater. Chem. A 5(47), 24836–24841 (2017). https://doi.org/10.1039/C7TA08982A
Benefitting from the ultrasmall monodispersed nanostructure and the strong
electronic synergy between Ir, Ni, and Fe, the resulting IrNi0.57Fe0.82 sample
allowed superior activity and high stability for both the HER and OER in 0.5 M
HClO4 aqueous solution. To yield a 10 mA cm−2 current density, this HER
overpotential was only 24 mV. Wang et al. synthesized the ultrafine Au
nanoparticles as acidic HER catalysts.130130. Y. Wang, Y. Sun, H. Liao, S. Sun,
S. Li, J. W. Ager, and Z. J. Xu, “ Activation effect of electrochemical cycling
on gold nanoparticles towards the hydrogen evolution reaction in sulfuric acid,”
Electrochim. Acta 209(10), 440–447 (2016).
https://doi.org/10.1016/j.electacta.2016.05.095 It was found that step-like
structures were formed in these Au NPs during the consecutive electrochemical
cycling process within the double layer region, which then triggered a dramatic
enhancement in the HER activity. Specifically, the overpotential and Tafel slope
was decreased by 128 mV and 23 mV dec−1, as well as, the TOF value had a nearly
twenty-time increase. Li et al. studied the effect of the Pd nanocube (NC) size
on the HER activity.134134. J. Li, P. Zhou, F. Li, J. Ma, Y. Liu, X. Zhang, H.
Huo, J. Jin, and J. Ma, “ Shape-controlled synthesis of Pd polyhedron supported
on polyethyleneimine-reduced graphene oxide for enhancing the efficiency of
hydrogen evolution reaction,” J. Power Sources 302(20), 343–351 (2016).
https://doi.org/10.1016/j.jpowsour.2015.10.050 Six samples with various particle
sizes, ranging from 4.1 nm to 13.7 nm, were produced based on a solvothermal
route with different halide species concentration (Br− and Cl−) and synthetic
temperatures. The Pd NCs with 9.7 nm width showed a nearly 100% purity and
afforded the optimal activity toward HER in acidic electrolytes.
Beyond the particle size, unique morphology may exhibit several novel physical
and/or chemical properties and subsequently optimize the catalytic
behavior.134,135134. J. Li, P. Zhou, F. Li, J. Ma, Y. Liu, X. Zhang, H. Huo, J.
Jin, and J. Ma, “ Shape-controlled synthesis of Pd polyhedron supported on
polyethyleneimine-reduced graphene oxide for enhancing the efficiency of
hydrogen evolution reaction,” J. Power Sources 302(20), 343–351 (2016).
https://doi.org/10.1016/j.jpowsour.2015.10.050135. T.-R. Kuo, Y.-C. Lee, H.-L.
Chou, M. G. Swathi, C.-Y. Wei, C.-Y. Wen, Y.-H. Chang, X.-Y. Pan, and D.-Y.
Wang, “ Plasmon-enhanced hydrogen evolution on specific facet of silver
nanocrystals,” Chem. Mater. 31(10), 3722–3728 (2019).
https://doi.org/10.1021/acs.chemmater.9b00652 In this aforementioned case
reported by Li et al., with the 9.7 nm-width Pd NCs as the seeds, different
amounts of metal source, Na2PdCl4, were further introduced to prepare Pd
nanoparticles with different shapes, i.e., truncated cubes, cuboctahedrons,
truncated octahedrons, and octahedrons.134134. J. Li, P. Zhou, F. Li, J. Ma, Y.
Liu, X. Zhang, H. Huo, J. Jin, and J. Ma, “ Shape-controlled synthesis of Pd
polyhedron supported on polyethyleneimine-reduced graphene oxide for enhancing
the efficiency of hydrogen evolution reaction,” J. Power Sources 302(20),
343–351 (2016). https://doi.org/10.1016/j.jpowsour.2015.10.050 With the shapes
varying from cube to octahedron, the proportions of Pd (100) to (111) crystal
planes gradually decreased and so did the HER activity in acidic solutions. DFT
calculations revealed that the Pd (100) facet had a higher electron density
relative to the Pd (111) facet, thus offering more electrons during the HER
process. Moreover, a stable intermediate state was more easily formed on the Pd
(100) surface than on the Pd (111) surface. Guided by this fundamental proof,
the same group subsequently fabricated the PdCu@Pd nanocubes with a Pt-like
activity for hydrogen production under acidic conditions.4848. J. Li, F. Li,
S.-X. Guo, J. Zhang, and J. Ma, “ PdCu@Pd nanocube with Pt-like activity for
hydrogen evolution reaction,” ACS Appl. Mater. Interfaces 9(9), 8151–8160
(2017). https://doi.org/10.1021/acsami.7b01241 Similarly, Kuo and his co-workers
recently reported the synthesis of well-defined silver nanocubes (AgNCs) with
(100) plane and nano-octahedra (AgNOs) with (111) plane and studied their
facet-dependent catalytic activities under acidic conditions.135135. T.-R. Kuo,
Y.-C. Lee, H.-L. Chou, M. G. Swathi, C.-Y. Wei, C.-Y. Wen, Y.-H. Chang, X.-Y.
Pan, and D.-Y. Wang, “ Plasmon-enhanced hydrogen evolution on specific facet of
silver nanocrystals,” Chem. Mater. 31(10), 3722–3728 (2019).
https://doi.org/10.1021/acs.chemmater.9b00652 It was observed that AgNOs (111)
had better intrinsic activity for the electrocatalytic HER than that of AgNCs
(100) without laser irradiation, which could be due to the fact that AgNOs (111)
had a lower hydrogen adsorption energy than AgNCs (100), thus leading to the
easier hydrogen desorption on the AgNO (111) surface.
In 1D/2D nanostructures with anisotropic electron transport, nanowires,
nanotubes, nanorods, and nanosheets have been widely reported to enhance the HER
performance.74,136–14474. J. Ahmed and Y. Mao, “ Ultrafine iridium oxide
nanorods synthesized by molten salt method toward electrocatalytic oxygen and
hydrogen evolution reactions,” Electrochim. Acta 212(10), 686–693 (2016).
https://doi.org/10.1016/j.electacta.2016.06.122136. J. Yang, Y. Ji, Q. Shao, N.
Zhang, Y. Li, and X. Huang, “ A universal strategy to metal wavy nanowires for
efficient electrochemical water splitting at pH-universal conditions,” Adv.
Funct. Mater. 28(41), 1803722 (2018). https://doi.org/10.1002/adfm.201803722137.
C. Zhang, S. Liu, Z. Mao, X. Liang, and B. Chen, “ Ag-Ni core-shell nanowires
with superior electrocatalytic activity for alkaline hydrogen evolution
reaction,” J. Mater. Chem. A 5(32), 16646–16652 (2017).
https://doi.org/10.1039/C7TA04220E138. L. Fu, F. Yang, G. Cheng, and W. Luo, “
Ultrathin Ir nanowires as high-performance electrocatalysts for efficient water
splitting in acidic media,” Nanoscale 10(4), 1892–1897 (2018).
https://doi.org/10.1039/C7NR09377B139. L. Zhang, L. Liu, H. Wang, H. Shen, Q.
Cheng, C. Yan, and S. Park, “ Electrodeposition of rhodium nanowires arrays and
their morphology-dependent hydrogen evolution activity,” Nanomaterials 7(5), 103
(2017). https://doi.org/10.3390/nano7050103140. Q. Lu, A. L. Wang, H. Cheng, Y.
Gong, Q. Yun, N. Yang, B. Li, B. Chen, Q. Zhang, and Y. Zong, “ Synthesis of
hierarchical 4H/fcc Ru nanotubes for highly efficient hydrogen evolution in
alkaline media,” Small 14(30), 1801090 (2018).
https://doi.org/10.1002/smll.201801090141. R. Nazir, U. Basak, and S. Pande, “
Synthesis of one-dimensional RuO2 nanorod for hydrogen and oxygen evolution
reaction: An efficient and stable electrocatalyst,” Colloids Surf. A 560(5),
141–148 (2019). https://doi.org/10.1016/j.colsurfa.2018.10.009142. Y. Han, Y.
Yan, Z. Wu, Y. Jiang, X. Li, Q. Xu, X. Yang, H. Zhang, and D. Yang, “ Facile
synthesis of Pd@Ru nanoplates with controlled thickness as efficient catalysts
for hydrogen evolution reaction,” CrystEngComm 20(30), 4230–4236 (2018).
https://doi.org/10.1039/C8CE00549D143. Y. Zhao, S. Xing, X. Meng, J. Zeng, S.
Yin, X. Li, and Y. Chen, “ Ultrathin Rh nanosheets as a highly efficient
bifunctional electrocatalyst for isopropanol-assisted overall water splitting,”
Nanoscale 11(19), 9319–9326 (2019). https://doi.org/10.1039/C9NR02153A144. X.
Kong, K. Xu, C. Zhang, J. Dai, S. Norooz Oliaee, L. Li, X. Zeng, C. Wu, and Z.
Peng, “ Free-standing two-dimensional Ru nanosheets with high activity toward
water splitting,” ACS Catal. 6(3), 1487–1492 (2016).
https://doi.org/10.1021/acscatal.5b02730 Huang's group proposed a facile and
universal approach to prepare diverse wavy noble metal nanowires (NWs).136136.
J. Yang, Y. Ji, Q. Shao, N. Zhang, Y. Li, and X. Huang, “ A universal strategy
to metal wavy nanowires for efficient electrochemical water splitting at
pH-universal conditions,” Adv. Funct. Mater. 28(41), 1803722 (2018).
https://doi.org/10.1002/adfm.201803722 The synthesis was based on a wet-chemical
route by uniformly mixing lead (II) formate [Pb(HCOO)2], polyvinylpyrrolidone
(PVP), and ethylene glycol (C2H6O2), with different metal raw materials
(K2RuCl5·H2O, IrCl3·xH2O, K2PtCl4, or RhCl3), and then undergoing a heat
treatment at 180 °C, for diverse noble metal products. As a consequence,
hcp-structured Ru and fcc-structured Rh, Ir, and Pt with the wavy nanowire shape
were attained, respectively, as shown in Figs. 15(a)–15(f). Such wavy nanowire
structures endowed these NMNs with ultrathin nature and massive defects that are
instructive for electrocatalysis. All as-prepared noble metal NWs exhibited the
outstanding HER performance comparable to the state-of-art Pt/C in both acidic
and alkaline electrolytes, where the Ir wave NWs were the optimal ones with the
overpotential of 15 and 38 mV at a 10 mA cm−2 current density in 0.5 M H2SO4 and
1 M KOH, respectively. Besides, these noble metal NWs as well as the RuO2 NWs
also showed attractive OER activity under both acidic and alkaline conditions,
especially RuO2 NWs. Coupling Ir NWs and RuO2 NWs, an efficient water-splitting
performance in different solutions was obtained, which was much superior to the
results of the commercial Ir/C-Pt/C electrolyzer [Fig. 15(g)]. Subsequently,
Huang's group further optimized the solid nanowires structure of Ir–Ag bimetal
at the nanoscale by selective acid etching treatment into hollow Ir–Ag
nanotubes.3434. M. Zhu, Q. Shao, Y. Qian, and X. Huang, “ Superior overall water
splitting electrocatalysis in acidic conditions enabled by bimetallic Ir-Ag
nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.023 According to experimental analysis,
the optimized hollow nanostructure offered a higher surface area, favoring the
formation of more active surface sites. Meanwhile, the surface was enriched in
oxidized Ir atoms, which was highly active for both OER and HER catalysis. The
synergistic control in morphological and electronic structures enabled the
hollow Ir–Ag nanotubes with excellent bifunctional performance for both the HER
and OER in the acidic environment. As another 1D nanostructure, IrO2 or RuO2
nanorods were also successfully constructed as highly efficient HER
electrocatalysts.74,14174. J. Ahmed and Y. Mao, “ Ultrafine iridium oxide
nanorods synthesized by molten salt method toward electrocatalytic oxygen and
hydrogen evolution reactions,” Electrochim. Acta 212(10), 686–693 (2016).
https://doi.org/10.1016/j.electacta.2016.06.122141. R. Nazir, U. Basak, and S.
Pande, “ Synthesis of one-dimensional RuO2 nanorod for hydrogen and oxygen
evolution reaction: An efficient and stable electrocatalyst,” Colloids Surf. A
560(5), 141–148 (2019). https://doi.org/10.1016/j.colsurfa.2018.10.009
FIG. 15. X-ray diffraction (XRD) patterns of (a) Ru, (b) Ir, Pt, and Rh NWs. TEM
images of (c) Ru, (d) Ir, (e) Pt, and (f) Rh NWs. (g) Overall water-splitting
polarization curves of this RuO2 NW–Ir NW couple and Ir/C-Pt/C in the
pH-universal electrolytes. Reproduced with permission from Yang et al., Adv.
Funct. Mater. 28(41), 1803722 (2018). Copyright 2018 Wiley-VCH.
* PPT
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* High-resolution
Regarding 2D nanosheets, ultrathin thickness is of paramount importance for
electrocatalytic behavior, owing to likely more exposed active
sites.11,68,142–14511. Y. Zhao, J. Bai, X.-R. Wu, P. Chen, P.-J. Jin, H.-C. Yao,
and Y. Chen, “ Atomically ultrathin RhCo alloy nanosheet aggregates for
efficient water electrolysis in broad pH range,” J. Mater. Chem. A 7(27),
16437–16446 (2019). https://doi.org/10.1039/C9TA05334D68. D. Zhang, H. Zhao, B.
Huang, B. Li, H. Li, Y. Han, Z. Wang, X. Wu, Y. Pan, and Y. Sun, “ Advanced
ultrathin RuPdM (M = Ni, Co, Fe) nanosheets electrocatalyst boosts hydrogen
evolution,” ACS Cent. Sci. 5(12), 1991–1997 (2019).
https://doi.org/10.1021/acscentsci.9b01110142. Y. Han, Y. Yan, Z. Wu, Y. Jiang,
X. Li, Q. Xu, X. Yang, H. Zhang, and D. Yang, “ Facile synthesis of Pd@Ru
nanoplates with controlled thickness as efficient catalysts for hydrogen
evolution reaction,” CrystEngComm 20(30), 4230–4236 (2018).
https://doi.org/10.1039/C8CE00549D143. Y. Zhao, S. Xing, X. Meng, J. Zeng, S.
Yin, X. Li, and Y. Chen, “ Ultrathin Rh nanosheets as a highly efficient
bifunctional electrocatalyst for isopropanol-assisted overall water splitting,”
Nanoscale 11(19), 9319–9326 (2019). https://doi.org/10.1039/C9NR02153A144. X.
Kong, K. Xu, C. Zhang, J. Dai, S. Norooz Oliaee, L. Li, X. Zeng, C. Wu, and Z.
Peng, “ Free-standing two-dimensional Ru nanosheets with high activity toward
water splitting,” ACS Catal. 6(3), 1487–1492 (2016).
https://doi.org/10.1021/acscatal.5b02730145. Q. Yao, B. Huang, N. Zhang, M. Sun,
Q. Shao, and X. Huang, “ Channel-rich RuCu nanosheets for pH-universal overall
water splitting electrocatalysis,” Angew. Chem., Int. Ed. 58(39), 13983–13988
(2019). https://doi.org/10.1002/anie.201908092 Kong et al. designed 2D Ru
nanosheets via a facile solvothermal strategy and employed them as HER
electrocatalysts.144144. X. Kong, K. Xu, C. Zhang, J. Dai, S. Norooz Oliaee, L.
Li, X. Zeng, C. Wu, and Z. Peng, “ Free-standing two-dimensional Ru nanosheets
with high activity toward water splitting,” ACS Catal. 6(3), 1487–1492 (2016).
https://doi.org/10.1021/acscatal.5b02730 The as-developed Ru nanosheets
possessed ultrathin dimensions with only 5–7 atomic layers, good crystallinity,
and a higher hydrogen adsorption (−0.289 eV) than the corresponding powder
counterpart (−0.392 eV). Accordingly, they afforded excellent activity in 0.5 M
H2SO4 aqueous solution, obviously better than the powder one. Zhao and his
co-workers reported a high-temperature cyanogel-reduction approach to synthesize
atomically thin RhCo nanosheet aggregates (RhCo-ANAs) with Rh fcc phase.1111. Y.
Zhao, J. Bai, X.-R. Wu, P. Chen, P.-J. Jin, H.-C. Yao, and Y. Chen, “ Atomically
ultrathin RhCo alloy nanosheet aggregates for efficient water electrolysis in
broad pH range,” J. Mater. Chem. A 7(27), 16437–16446 (2019).
https://doi.org/10.1039/C9TA05334D These nanosheets were about only 1.3 nm thin
and chemically stable. They could serve as a robust electrocatalyst toward both
the OER and HER in all pH ranges. In particular, under the neutral conditions
where the electrocatalysis was relatively difficult to occur, RhCo nanosheet
aggregates catalyzed the HER and OER with the η10 of only 31 and 310 mV,
respectively, far lower than that of the benchmark samples, i.e., Pt/C and RuO2
(55 and 480 mV, respectively). In 0.5 M H2SO4 and 1 M KOH solutions, the RhCo
nanosheet aggregates also displayed better HER and OER activities than the
benchmark Pt/C and RuO2 samples, respectively [HER: RhCo: η10 = 12.4/32.4 mV
(0.5 M H2SO4/1 M KOH); Pt/C: η10 = 17.4/56.4 mV (0.5 M H2SO4/1 M KOH)] [OER:
RhCo: η10 = ∼250 mV (0.5 M H2SO4/1 M KOH); RuO2: η10 = ∼350 mV (0.5 M H2SO4/1 M
KOH)]. Besides, a remarkable stability was obtained for this catalyst. To
further optimize the ultrathin nanosheet structure for enhancing the catalytic
ability, constructing holes in them is an effective pathway that could largely
increase the density of active sites, improve the mass transport efficiency, and
promote electron transfer. However, it is still a challenging job for
researchers and there are very few studies about the development of ultrathin
noble metal NSs with porous structures. Li's group demonstrated the synthesis of
a novel ordered porous nanosheet, i.e., an ultrathin Pd nanomesh (NM) through a
top–down approach.1919. J. Ge, P. Wei, G. Wu, Y. Liu, T. Yuan, Z. Li, Y. Qu, Y.
Wu, H. Li, and Z. Zhuang, “ Ultrathin palladium nanomesh for electrocatalysis,”
Angew. Chem., Int. Ed. 130(13), 3493–3496 (2018).
https://doi.org/10.1002/ange.201800552 As depicted in Fig. 16(a), the initially
obtained ultrathin Pd NSs were dispersed in a mixed solution of
N,N-dimethylformamide (DMF) and distilled water with a volume ratio of 1:1 and
then kept in ambient environment for 4 weeks, during which the moderate
oxidative etching and removal of palladium atoms appeared, eventually generating
the Pd NMs successfully. Noticeably, a slow or fast oxidative etching process by
varying the operation conditions could lead to an unsuccessful transformation,
with the formation of preserved Pd NSs and Pd wavy nanowires, respectively. The
TEM images in Figs. 16(b) and 16(c) illustrated that in the ultrathin Pd NMs,
ordered trigonal holes were widely created among the densely arrayed
quasi-nanoribbons, and the corresponding width in average for holes and
quasi-nanoribbons were approximately 11.4 and 3.4 nm, respectively.
Additionally, according to the atomic force microscopy (AFM) measurements [Fig.
16(d)], the thickness of the Pd NSs was about 3.3 nm. In 0.5 M H2SO4, the Pd NMs
exhibited high HER activity with a low η10 of 59.3 mV, which was close to the
data of Pt/C [Fig. 16(e)]. After loading ultrafine Pt nanoparticles on Pd NMs
(Pd NM/Pt, Pt: 13 wt. %), a smaller η10 of 21.3 mV was required, even surpassing
Pt/C (27.7 mV). Furthermore, thanks to the unique nanostructure, the prominent
activity of Pd NM/Pt was sustained after 2000 continuous cycles, while a 21%
current drop under the overpotential of 50 mV was observed for the commercial
Pt/C [Fig. 16(f)]. This finding opens a new avenue for designing unique porous
framework in ultrathin 2D noble-metal NSs. Apart from the above three studies,
there are also other studies on ultrathin 2D nanosheets as electrocatalysts for
the HER, such as Rh NSs, Rh2P NSs, RuPdM (M = Fe, Co, and Ni) NSs, RuCu NSs, and
so forth.68,84,143,14568. D. Zhang, H. Zhao, B. Huang, B. Li, H. Li, Y. Han, Z.
Wang, X. Wu, Y. Pan, and Y. Sun, “ Advanced ultrathin RuPdM (M = Ni, Co, Fe)
nanosheets electrocatalyst boosts hydrogen evolution,” ACS Cent. Sci. 5(12),
1991–1997 (2019). https://doi.org/10.1021/acscentsci.9b0111084. K. Wang, B.
Huang, F. Lin, F. Lv, M. Luo, P. Zhou, Q. Liu, W. Zhang, C. Yang, and Y. Tang, “
Wrinkled Rh2P nanosheets as superior pH-universal electrocatalysts for hydrogen
evolution catalysis,” Adv. Energy Mater. 8(27), 1801891 (2018).
https://doi.org/10.1002/aenm.201801891143. Y. Zhao, S. Xing, X. Meng, J. Zeng,
S. Yin, X. Li, and Y. Chen, “ Ultrathin Rh nanosheets as a highly efficient
bifunctional electrocatalyst for isopropanol-assisted overall water splitting,”
Nanoscale 11(19), 9319–9326 (2019). https://doi.org/10.1039/C9NR02153A145. Q.
Yao, B. Huang, N. Zhang, M. Sun, Q. Shao, and X. Huang, “ Channel-rich RuCu
nanosheets for pH-universal overall water splitting electrocatalysis,” Angew.
Chem., Int. Ed. 58(39), 13983–13988 (2019).
https://doi.org/10.1002/anie.201908092
FIG. 16. (a) Illustration of the formation route of the ultrathin Pd NMs. (b)
TEM and (c) HAADF-STEM images of Pd NMs. (d) The AFM result of Pd NMs. (e) HER
polarization curves of Pd NMs/Pt, Pd NMs, and Pt/C in the acidic electrolyte.
(f) The stability testing of Pd NMs/Pt and Pt/C. Reproduced with permission from
Ge et al., Angew. Chem., Int. Ed. 130(13), 3493–3496 (2018). Copyright 2018
Wiley-VCH.
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* High-resolution
In Huang's group, different morphologies of metallic Rh, including tetrahedron
(TH), concave tetrahedron (CT), and 2D nanosheet (NS), were well developed via
simply tuning the OAm: 1-octadecene (ODE) volume ratio in the precursor solution
(OAm: oleylamine and ODE: 1-octadecene), as observed from Figs.
17(a)–17(g).1515. N. Zhang, Q. Shao, Y. Pi, J. Guo, and X. Huang, “
Solvent-mediated shape tuning of well-defined rhodium nanocrystals for efficient
electrochemical water splitting,” Chem. Mater. 29(11), 5009–5015 (2017).
https://doi.org/10.1021/acs.chemmater.7b01588 Here, the different solvents with
different reducing abilities governed the growth of diverse well-defined shapes.
Experimental results suggested that the HER performance of metallic Rh
nanomaterials was largely dependent on their morphologies. Rh NSs possessed a
relatively larger electrochemical specific surface area and lower hydrogen
binding energy, thus giving a better catalytic activity in the alkaline HER,
even far outperforming Pt/C [Fig. 17(h)]. In the last year, a parallel study
about various forms of Ag nanocrystals containing nanocube, nanowire, and
nanosphere was also conducted by Mo et al.146146. J. Mo, B. I. Stefanov, T. H.
Lau, T. Chen, S. Wu, Z. Wang, X.-Q. Gong, I. Wilkinson, G. n Schmid, and S. C.
E. Tsang, “ Superior performance of Ag over Pt for hydrogen evolution reaction
in water electrolysis under high overpotentials,” ACS Appl. Energy Mater. 2(2),
1221–1228 (2019). https://doi.org/10.1021/acsaem.8b01777 They noticed that the
Ag nanocubes had the highest HER activity at the applied potential of −1.5 V
among the three forms owing to the lowest H adsorption strength. Rh2P, with
three nanostructures of monodisperse nanoparticle, monodisperse nanocube, and
wrinkled nanosheet, was reported by three different groups, respectively, all of
which demonstrated the phenomenal catalytic activity for HER in pH-universal
electrolytes, obviously better than Pt/C. Figure 17(i) listed the comparison of
their HER activity.80,84,8580. H. Duan, D. Li, Y. Tang, Y. He, S. Ji, R. Wang,
H. Lv, P. P. Lopes, A. P. Paulikas, and H. Li, “ High-performance Rh2P
electrocatalyst for efficient water splitting,” J. Am. Chem. Soc. 139(15),
5494–5502 (2017). https://doi.org/10.1021/jacs.7b0137684. K. Wang, B. Huang, F.
Lin, F. Lv, M. Luo, P. Zhou, Q. Liu, W. Zhang, C. Yang, and Y. Tang, “ Wrinkled
Rh2P nanosheets as superior pH-universal electrocatalysts for hydrogen evolution
catalysis,” Adv. Energy Mater. 8(27), 1801891 (2018).
https://doi.org/10.1002/aenm.20180189185. F. Yang, Y. Zhao, Y. Du, Y. Chen, G.
Cheng, S. Chen, and W. Luo, “ A monodisperse Rh2P-based electrocatalyst for
highly efficient and pH-universal hydrogen evolution reaction,” Adv. Energy
Mater. 8(18), 1703489 (2018). https://doi.org/10.1002/aenm.201703489
FIG. 17. (a) The synthetic procedure of the metallic Rh with different
morphologies. (b), (d), and (f) TEM and (c), (e), and (g) HAADF-STEM images of
Rh THs (b) and (c), Rh CTs (d) and (e), and Rh NSs (f) and (g). (h) HER
polarization curves of Rh THs, Rh CTs, Rh NSs, Rh/C, and Pt/C in 1 M KOH.
Reproduced with permission from Zhang et al., Chem. Mater. 29(11), 5009–5015
(2017). Copyright 2017 American Chemical Society. (i) The comparison of HER
activities of Rh2P with different nanostructures. (j) The formation route of the
spongy-like nanoporous Ag foam. (k) The HER activity of different Ag electrodes
and Pt in 0.5 M H2SO4. Reproduced with permission from Huang et al., ACS
Sustainable Chem. Eng. 6(7), 8285–8290 (2018). Copyright 2018 American Chemical
Society.
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* High-resolution
Different from the above studies, several researchers also attempted to
synthesize large-area and high-quality 3D porous nanoarchitectures.147,148147.
H. Begum, M. S. Ahmed, and S. Jeon, “ Highly efficient dual active palladium
nanonetwork electrocatalyst for ethanol oxidation and hydrogen evolution,” ACS
Appl. Mater. Interfaces 9(45), 39303–39311 (2017).
https://doi.org/10.1021/acsami.7b09855148. J.-F. Huang and Y.-C. Wu, “ Making Ag
present Pt-like activity for hydrogen evolution reaction,” ACS Sustainable Chem.
Eng. 6(7), 8285–8290 (2018). https://doi.org/10.1021/acssuschemeng.8b00295 Begum
et al. presented the usage of a facile chemical method by the aid of the Zn
precursor and cetyltrimethylammonium bromide (CTAB) surfactant to produce a 3D
palladium nanonetwork (PdNN), in which the thickness of this network could be
tunable via simply controlling the CTAB amount.147147. H. Begum, M. S. Ahmed,
and S. Jeon, “ Highly efficient dual active palladium nanonetwork
electrocatalyst for ethanol oxidation and hydrogen evolution,” ACS Appl. Mater.
Interfaces 9(45), 39303–39311 (2017). https://doi.org/10.1021/acsami.7b09855 The
as-obtained optimized PdNN had good 3D porous nanoarchitecture that was
interwoven by plenty of 1D rod-like structures with a mean diameter of 4.9 nm.
Such a unique 3D nanonetwork accelerated the electron transfer for the HER
process and a large electrochemical area provided highly HER active sites.
Accordingly, its HER catalytic behavior under alkaline conditions was
strengthened, in comparison with the particle counterparts. Also, based on an
electrochemical surface treatment [Fig. 17(j)], an analogous nanomaterial, i.e.,
a spongy-like nanoporous Ag foam, was fabricated by Huang and Wu.148148. J.-F.
Huang and Y.-C. Wu, “ Making Ag present Pt-like activity for hydrogen evolution
reaction,” ACS Sustainable Chem. Eng. 6(7), 8285–8290 (2018).
https://doi.org/10.1021/acssuschemeng.8b00295 The treatment followed the
repetitively electrochemical anodic formation of AgX (I, Br, or Cl)/cathodic
reduction back to Ag (notably, the Ag product was named as AgX), where the
growth rate of Ag played a crucial role in the final microstructure. Among three
kinds of silver halides, the reducible ability of AgBr is neither strong nor
weak, and hence causes a moderate Ag growth rate to finally form the
high-density nanosized ligament in the Ag nanoporous network. As a HER
electrocatalyst in 0.5 M H2SO4, the onset overpotential of AgBr800 delivered an
extraordinary diminution to 50 mV, which was around 200, 350, and 370 mV smaller
than AgCl800, AgI800, and the pristine Ag, respectively, as seen from Fig.
17(k).
A summary of the catalytic behavior toward the HER for various representative
non-Pt NMN electrocatalysts with differed shapes in different media is shown in
Table II.
TABLE II. Performance of various representative non-Pt NMN electrocatalysts with
differed shapes.
Catalyst Electrolyte Loading (mg cm−2) Overpotential η10 (mV) Tafel slope (mV
dec−1) Stability References Ru@NG-2 1 M H2SO4 0.857 74 48 5000 CV or −100 mV @
10 h 129129. B. K. Barman, D. Das, and K. K. Nanda, “ Facile synthesis of
ultrafine Ru nanocrystal supported N-doped graphene as an exceptional hydrogen
evolution electrocatalyst in both alkaline and acidic media,” Sustainable Energy
Fuels 1(5), 1028–1033 (2017). https://doi.org/10.1039/C7SE00153C 1 M KOH 47 82
IrNi0.57Fe0.82 NPs 0.5 M HClO4 92 μgIr cm−2 24 34.6 1000 CV or −10 mA cm−2 @ 5.5
h 6464. L. Fu, G. Cheng, and W. Luo, “ Colloidal synthesis of monodisperse
trimetallic IrNiFe nanoparticles as highly active bifunctional electrocatalysts
for acidic overall water splitting,” J. Mater. Chem. A 5(47), 24836–24841
(2017). https://doi.org/10.1039/C7TA08982A Au NPs 0.5 M H2SO4 … 128 23 … 130130.
Y. Wang, Y. Sun, H. Liao, S. Sun, S. Li, J. W. Ager, and Z. J. Xu, “ Activation
effect of electrochemical cycling on gold nanoparticles towards the hydrogen
evolution reaction in sulfuric acid,” Electrochim. Acta 209(10), 440–447 (2016).
https://doi.org/10.1016/j.electacta.2016.05.095 Pd NCs 0.5 M H2SO4 0.14 37
(onset) 62 … 134134. J. Li, P. Zhou, F. Li, J. Ma, Y. Liu, X. Zhang, H. Huo, J.
Jin, and J. Ma, “ Shape-controlled synthesis of Pd polyhedron supported on
polyethyleneimine-reduced graphene oxide for enhancing the efficiency of
hydrogen evolution reaction,” J. Power Sources 302(20), 343–351 (2016).
https://doi.org/10.1016/j.jpowsour.2015.10.050 Pd Octahedrons >150 (onset) 98 …
AgNCs 0.5 M H2SO4 >300 … 135135. T.-R. Kuo, Y.-C. Lee, H.-L. Chou, M. G. Swathi,
C.-Y. Wei, C.-Y. Wen, Y.-H. Chang, X.-Y. Pan, and D.-Y. Wang, “ Plasmon-enhanced
hydrogen evolution on specific facet of silver nanocrystals,” Chem. Mater.
31(10), 3722–3728 (2019). https://doi.org/10.1021/acs.chemmater.9b00652 AgNOs
>400 … Ir NWs 0.05 M H2SO4 40.7 μgIr cm−2 17 26 … 136136. J. Yang, Y. Ji, Q.
Shao, N. Zhang, Y. Li, and X. Huang, “ A universal strategy to metal wavy
nanowires for efficient electrochemical water splitting at pH-universal
conditions,” Adv. Funct. Mater. 28(41), 1803722 (2018).
https://doi.org/10.1002/adfm.201803722 0.5 M H2SO4 15 34 … 0.1 M KOH 73 46 … 1 M
KOH 38 30 … Ir6Ag9 NTs 0.5 M H2SO4 13.3 μgIr cm−2 20 27.5 −5 mA cm−2 @ 5 h 3434.
M. Zhu, Q. Shao, Y. Qian, and X. Huang, “ Superior overall water splitting
electrocatalysis in acidic conditions enabled by bimetallic Ir-Ag nanotubes,”
Nano Energy 56, 330–337 (2019). https://doi.org/10.1016/j.nanoen.2018.11.023 Ru
nanosheet 0.5 M H2SO4 0.102 20 46 … 144144. X. Kong, K. Xu, C. Zhang, J. Dai, S.
Norooz Oliaee, L. Li, X. Zeng, C. Wu, and Z. Peng, “ Free-standing
two-dimensional Ru nanosheets with high activity toward water splitting,” ACS
Catal. 6(3), 1487–1492 (2016). https://doi.org/10.1021/acscatal.5b02730 Ru
powder 30 76 … RhCo-ANAs 0.5 M H2SO4 2 12.4 30.7 … 1111. Y. Zhao, J. Bai, X.-R.
Wu, P. Chen, P.-J. Jin, H.-C. Yao, and Y. Chen, “ Atomically ultrathin RhCo
alloy nanosheet aggregates for efficient water electrolysis in broad pH range,”
J. Mater. Chem. A 7(27), 16437–16446 (2019). https://doi.org/10.1039/C9TA05334D
1 M PBS 31 33.6 −50 mV @ 5 h 1 M KOH 32.4 31.9 … Pd NMs 0.5 M H2SO4 0.02 59.3 57
… 1919. J. Ge, P. Wei, G. Wu, Y. Liu, T. Yuan, Z. Li, Y. Qu, Y. Wu, H. Li, and
Z. Zhuang, “ Ultrathin palladium nanomesh for electrocatalysis,” Angew. Chem.,
Int. Ed. 130(13), 3493–3496 (2018). https://doi.org/10.1002/ange.201800552 Rh
THs 0.1 M KOH 15.3 μgRh cm−2 64 79.5 −5 mA cm−2 @ 5 h 1515. N. Zhang, Q. Shao,
Y. Pi, J. Guo, and X. Huang, “ Solvent-mediated shape tuning of well-defined
rhodium nanocrystals for efficient electrochemical water splitting,” Chem.
Mater. 29(11), 5009–5015 (2017). https://doi.org/10.1021/acs.chemmater.7b01588 1
M KOH 63 113.5 Rh CTs 0.1 M KOH 66 117.7 1 M KOH 84 114.2 Rh NSs 0.1 M KOH 37
74.7 1 M KOH 43 107.2 Monodisperse Rh2P NPs 0.5 M H2SO4 0.0306 14 31.7 1000 CV
8585. F. Yang, Y. Zhao, Y. Du, Y. Chen, G. Cheng, S. Chen, and W. Luo, “ A
monodisperse Rh2P-based electrocatalyst for highly efficient and pH-universal
hydrogen evolution reaction,” Adv. Energy Mater. 8(18), 1703489 (2018).
https://doi.org/10.1002/aenm.201703489 1 M PBS 38 46 1 M KOH 30 50 w-Rh2P NS 0.1
M HClO4 0.0123 15.8 29.9 1000 CV 8484. K. Wang, B. Huang, F. Lin, F. Lv, M. Luo,
P. Zhou, Q. Liu, W. Zhang, C. Yang, and Y. Tang, “ Wrinkled Rh2P nanosheets as
superior pH-universal electrocatalysts for hydrogen evolution catalysis,” Adv.
Energy Mater. 8(27), 1801891 (2018). https://doi.org/10.1002/aenm.201801891 0.1
M PBS 21.9 78.4 0.1 M KOH 18.3 61.5 Monodisperse Rh2P NCs 0.5 M H2SO4 3.7 μgRh
cm−2 ∼8 … −1.72 mA mgmetal−1 @ 2000 s 8080. H. Duan, D. Li, Y. Tang, Y. He, S.
Ji, R. Wang, H. Lv, P. P. Lopes, A. P. Paulikas, and H. Li, “ High-performance
Rh2P electrocatalyst for efficient water splitting,” J. Am. Chem. Soc. 139(15),
5494–5502 (2017). https://doi.org/10.1021/jacs.7b01376 3D PdNN 1 M KOH 16.9 μgPd
cm−2 110 121 1000 CV or −110 mA cm−2 @ 4.2 h 147147. H. Begum, M. S. Ahmed, and
S. Jeon, “ Highly efficient dual active palladium nanonetwork electrocatalyst
for ethanol oxidation and hydrogen evolution,” ACS Appl. Mater. Interfaces
9(45), 39303–39311 (2017). https://doi.org/10.1021/acsami.7b09855 PdNPs 22.6
μgPd cm−2 170 133 Nanoporous Ag foam AgBr800 0.5 M H2SO4 … 50 (onset) 119 5000
CV or −0.12/0.15/0.18 V @ 60 h 148148. J.-F. Huang and Y.-C. Wu, “ Making Ag
present Pt-like activity for hydrogen evolution reaction,” ACS Sustainable Chem.
Eng. 6(7), 8285–8290 (2018). https://doi.org/10.1021/acssuschemeng.8b00295
C. Hybrid composite engineering
1. Bimetallic composites
As for the bimetallic nanostructures, apart from the conventional alloys, the
novel core–shell-structured composites also have become the hotspot of the HER
research field in the recent years.149–153149. Y. Luo, X. Luo, G. Wu, Z. Li, G.
Wang, B. Jiang, Y. Hu, T. Chao, H. Ju, and J. Zhu, “ Mesoporous Pd@ Ru
core-shell nanorods for hydrogen evolution reaction in alkaline solution,” ACS
Appl. Mater. Interfaces 10(40), 34147–34152 (2018).
https://doi.org/10.1021/acsami.8b09988150. C. Yang, H. Lei, W. Zhou, J. Zeng, Q.
Zhang, Y. Hua, and C. Xu, “ Engineering nanoporous Ag/Pd core/shell interfaces
with ultrathin Pt doping for efficient hydrogen evolution reaction over a wide
pH range,” J. Mater. Chem. A 6(29), 14281–14290 (2018).
https://doi.org/10.1039/C8TA04059A151. X. Wang, Y. Zhu, A. Vasileff, Y. Jiao, S.
Chen, L. Song, B. Zheng, Y. Zheng, and S.-Z. Qiao, “ Strain effect in bimetallic
electrocatalysts in the hydrogen evolution reaction,” ACS Energy Lett. 3(5),
1198–1204 (2018). https://doi.org/10.1021/acsenergylett.8b00454152. Y.-C. Shi,
S.-S. Chen, J.-J. Feng, X.-X. Lin, W. Wang, and A.-J. Wang, “ Dicationic ionic
liquid mediated fabrication of Au@Pt nanoparticles supported on reduced graphene
oxide with highly catalytic activity for oxygen reduction and hydrogen
evolution,” Appl. Surf. Sci. 441(31), 438–447 (2018).
https://doi.org/10.1016/j.apsusc.2018.01.240153. H. Liao, C. Wei, J. Wang, A.
Fisher, T. Sritharan, Z. Feng, and Z. J. Xu, “ A multisite strategy for
enhancing the hydrogen evolution reaction on a nano-Pd surface in alkaline
media,” Adv. Energy Mater. 7(21), 1701129 (2017).
https://doi.org/10.1002/aenm.201701129 Such nanostructures often exhibit
improved catalytic properties for the HER because of a lattice strain generated
in the boundary region of an ultrafine shell and internal core as well as a
synergy during the course of electrocatalytic hydrogen production. In this topic
about the noble metals, this core–shell structure with noble metal and noble
metal or noble metal and transition metal are both exploited by different
research teams.149–155149. Y. Luo, X. Luo, G. Wu, Z. Li, G. Wang, B. Jiang, Y.
Hu, T. Chao, H. Ju, and J. Zhu, “ Mesoporous Pd@ Ru core-shell nanorods for
hydrogen evolution reaction in alkaline solution,” ACS Appl. Mater. Interfaces
10(40), 34147–34152 (2018). https://doi.org/10.1021/acsami.8b09988150. C. Yang,
H. Lei, W. Zhou, J. Zeng, Q. Zhang, Y. Hua, and C. Xu, “ Engineering nanoporous
Ag/Pd core/shell interfaces with ultrathin Pt doping for efficient hydrogen
evolution reaction over a wide pH range,” J. Mater. Chem. A 6(29), 14281–14290
(2018). https://doi.org/10.1039/C8TA04059A151. X. Wang, Y. Zhu, A. Vasileff, Y.
Jiao, S. Chen, L. Song, B. Zheng, Y. Zheng, and S.-Z. Qiao, “ Strain effect in
bimetallic electrocatalysts in the hydrogen evolution reaction,” ACS Energy
Lett. 3(5), 1198–1204 (2018). https://doi.org/10.1021/acsenergylett.8b00454152.
Y.-C. Shi, S.-S. Chen, J.-J. Feng, X.-X. Lin, W. Wang, and A.-J. Wang, “
Dicationic ionic liquid mediated fabrication of Au@Pt nanoparticles supported on
reduced graphene oxide with highly catalytic activity for oxygen reduction and
hydrogen evolution,” Appl. Surf. Sci. 441(31), 438–447 (2018).
https://doi.org/10.1016/j.apsusc.2018.01.240153. H. Liao, C. Wei, J. Wang, A.
Fisher, T. Sritharan, Z. Feng, and Z. J. Xu, “ A multisite strategy for
enhancing the hydrogen evolution reaction on a nano-Pd surface in alkaline
media,” Adv. Energy Mater. 7(21), 1701129 (2017).
https://doi.org/10.1002/aenm.201701129154. T. Bian, B. Xiao, B. Sun, L. Huang,
S. Su, Y. Jiang, J. Xiao, A. Yuan, H. Zhang, and D. Yang, “ Local epitaxial
growth of Au-Rh core-shell star-shaped decahedra: A case for studying electronic
and ensemble effects in hydrogen evolution reaction,” Appl. Catal. B 263, 118255
(2020). https://doi.org/10.1016/j.apcatb.2019.118255155. Z. Zong, K. Xu, D. Li,
Z. Tang, W. He, Z. Liu, X. Wang, and Y. Tian, “ Peptide templated Au@ Pd
core-shell structures as efficient bi-functional electrocatalysts for both
oxygen reduction and hydrogen evolution reactions,” J. Catal. 361, 168–176
(2018). https://doi.org/10.1016/j.jcat.2018.02.020 Li's group, by using a
combined solvothermal process, proposed the successful preparation of Pd@Ru
core–shell nanorods with mesoporous structures, in which Pd and Ru were indexed
to the face centered cubic phase (fcc) and the hexagonal close-packed phase
(hcp).149149. Y. Luo, X. Luo, G. Wu, Z. Li, G. Wang, B. Jiang, Y. Hu, T. Chao,
H. Ju, and J. Zhu, “ Mesoporous Pd@ Ru core-shell nanorods for hydrogen
evolution reaction in alkaline solution,” ACS Appl. Mater. Interfaces 10(40),
34147–34152 (2018). https://doi.org/10.1021/acsami.8b09988 With the presence of
the Ru/Pd interface, an improved electrocatalytic property for alkaline HER with
a low overpotential of 30 mV at a current density of 10 mA cm−2 and much large
mass activity of 722.9 A g−1 at the overpotential of 60 mV was observed in
comparison with pure Pd and Ru. In the Qiao's group, the reported core–shell
Ru@Pt nanostructure expressed much more excellent HER catalytic peculiarities
than the conventional strain-free RuPt alloy.151151. X. Wang, Y. Zhu, A.
Vasileff, Y. Jiao, S. Chen, L. Song, B. Zheng, Y. Zheng, and S.-Z. Qiao, “
Strain effect in bimetallic electrocatalysts in the hydrogen evolution
reaction,” ACS Energy Lett. 3(5), 1198–1204 (2018).
https://doi.org/10.1021/acsenergylett.8b00454 The strain effect on the Pt
structure induced by Ru core dominantly enhanced the HER intrinsic activity in
the alkaline environment. Specifically, the Pt shells with a highly compressive
strain effectively accommodated an interfacial lattice mismatch from the
fcc-structured Ru core, which enabled better interaction towards both hydrogen
and hydroxyl species during this reaction, in turn, accelerating the ensemble
HER process. Based on a most recent work by Bian et al., the core–shell Au–Rh
star-shaped decahedra was synthesized via the seed-mediated growth with
decahedral Au nanoparticles as seeds.154154. T. Bian, B. Xiao, B. Sun, L. Huang,
S. Su, Y. Jiang, J. Xiao, A. Yuan, H. Zhang, and D. Yang, “ Local epitaxial
growth of Au-Rh core-shell star-shaped decahedra: A case for studying electronic
and ensemble effects in hydrogen evolution reaction,” Appl. Catal. B 263, 118255
(2020). https://doi.org/10.1016/j.apcatb.2019.118255 From the HRTEM
observations, these as-prepared core–shell nanoparticles showed a diameter of
about 10 nm and the (111) planes were the dominated exposed facets [Figs. 18(a)
and 18(b)]. By adjusting the amounts of Rh precursors, the researcher tuned the
thickness of Rh shell. To yield the 10 mA cm−2 current density in the 0.5 M
H2SO4 electrolyte, the optimal core–shell Au75Rh25 decahedra needed an
overpotential of 64.1 mV, lower than the value of the Rh/C catalyst by 39.4 mV
[Fig. 18(c)] and its Tafel slope (33.8 mV dec−1) was also comparable to the
benchmark Pt/C (30.2 mV dec−1) [Fig. 18(d)]. As the authors corroborated using
computational calculations [Figs. 18(e) and 18(f)], the ensemble effect played
the dominating role in promoting the hydrogen-production reaction rate by
exposing some Au atoms on the Rh surface instead of the complete coverage by Rh
shells. For the core–shell nanostructures composed of noble metal and TMs,
core–shell Ag–Ni nanowires manifested superior HER activity under the alkaline
conditions.137137. C. Zhang, S. Liu, Z. Mao, X. Liang, and B. Chen, “ Ag-Ni
core-shell nanowires with superior electrocatalytic activity for alkaline
hydrogen evolution reaction,” J. Mater. Chem. A 5(32), 16646–16652 (2017).
https://doi.org/10.1039/C7TA04220E The pronounced electron interplay from the
inter Ag gave rise to a remarkable increase in the catalytic performance when
the optimized Ag/Ni atomic ratio was 1:1. Besides, the 1D nanostructure and
conductive Ag nanowires further favored the HER by the exposure of more surface
active sites and rapid charge transport. Starting with core–shell Pd/Fe3O4
nanoparticles, Xu's group adopted the electrochemical cycling to control
coverage of FeOx(OH)2 − 2x on the Pd surface [Figs. 19(a) and 19(b)], which
provided additional water-dissociation sites for increasing the proton
supply.153153. H. Liao, C. Wei, J. Wang, A. Fisher, T. Sritharan, Z. Feng, and
Z. J. Xu, “ A multisite strategy for enhancing the hydrogen evolution reaction
on a nano-Pd surface in alkaline media,” Adv. Energy Mater. 7(21), 1701129
(2017). https://doi.org/10.1002/aenm.201701129 Markedly, at 40% coverage, the
HER activity was improved by 19 folds of the results of pure Pd NPs [Fig.
19(c)], because such coverage could balance the water-dissociation rate and
hydrogen-recombination rate to reach the highest efficiency. Besides these above
studies, Ir–Ag core–shell nanotubes, Au@Pd core–shell nanoparticles, Au–Pt
core–shell nanoparticles, core–shell Pt@Pd nanoflowers, Co@Pd core–shell
nanoparticles, and Ni@Pd core–shell nanospheres are also proposed for the
electrocatalytic HER.34,155–15934. M. Zhu, Q. Shao, Y. Qian, and X. Huang, “
Superior overall water splitting electrocatalysis in acidic conditions enabled
by bimetallic Ir-Ag nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.023155. Z. Zong, K. Xu, D. Li, Z. Tang,
W. He, Z. Liu, X. Wang, and Y. Tian, “ Peptide templated Au@ Pd core-shell
structures as efficient bi-functional electrocatalysts for both oxygen reduction
and hydrogen evolution reactions,” J. Catal. 361, 168–176 (2018).
https://doi.org/10.1016/j.jcat.2018.02.020156. Y. Shi, T.-T. Zhai, Y. Zhou,
W.-X. Xu, D.-R. Yang, F.-B. Wang, and X.-H. Xia, “ Atomic level tailoring of the
electrocatalytic activity of Au-Pt core-shell nanoparticles with controllable Pt
layers toward hydrogen evolution reaction,” J. Electroanal. Chem. 819(15),
442–446 (2018). https://doi.org/10.1016/j.jelechem.2017.12.006157. X.-X. Lin,
A.-J. Wang, K.-M. Fang, J. Yuan, and J.-J. Feng, “ One-pot seedless aqueous
synthesis of reduced graphene oxide (rGO)-supported core-shell Pt@Pd nanoflowers
as advanced catalysts for oxygen reduction and hydrogen evolution,” ACS
Sustainable Chem. Eng. 5(10), 8675–8683 (2017).
https://doi.org/10.1021/acssuschemeng.7b01400158. H. Yang, Z. Tang, K. Wang, W.
Wu, Y. Chen, Z. Ding, Z. Liu, and S. Chen, “ Co@Pd core-shell nanoparticles
embedded in nitrogen-doped porous carbon as dual functional electrocatalysts for
both oxygen reduction and hydrogen evolution reactions,” J. Colloid Interface
Sci. 528(15), 18–26 (2018). https://doi.org/10.1016/j.jcis.2018.05.063159. J.
Li, P. Zhou, F. Li, R. Ren, Y. Liu, J. Niu, J. Ma, X. Zhang, M. Tian, and J.
Jin, “ Ni@ Pd/PEI-rGO stack structures with controllable Pd shell thickness as
advanced electrodes for efficient hydrogen evolution,” J. Mater. Chem. A 3(21),
11261–11268 (2015). https://doi.org/10.1039/C5TA01805F
FIG. 18. (a) TEM and (b) HRTEM images of the core–shell Au–Rh star-shaped
decahedra. (c) HER polarization curves and (d) the corresponding Tafel plots of
Au68Rh32, Au75Rh25, Au84Rh16, Rh/C, and Pt/C in acidic media. The free energy
diagrams of (e) the core–shell structure and (f) alloyed structure. Reproduced
with permission from Bian et al., Appl. Catal. B 263, 118255 (2020). Copyright
2020 Elsevier.
* PPT
|
* High-resolution
FIG. 19. TEM images of (a) Pd nanoparticles and (b) core–shell Pd/Fe3O4
nanoparticles. (c) The HER activity as a function of the FeOx(OH)2 − 2x
coverage. Reproduced with permission from Liao et al., Adv. Energy Mater. 7(21),
1701129 (2017). Copyright 2017 Wiley-VCH.
* PPT
|
* High-resolution
Slightly different from the simple core (monometal)–shell (monometal) structure,
some groups utilized the bimetallic alloy as the core or shell for further
amelioration of the activity.60,160–16360. J. Wang, H. Zhu, D. Yu, J. Chen, J.
Chen, M. Zhang, L. Wang, and M. Du, “ Engineering the composition and structure
of bimetallic Au-Cu alloy nanoparticles in carbon nanofibers: Self-supported
electrode materials for electrocatalytic water splitting,” ACS Appl. Mater.
Interfaces 9(23), 19756–19765 (2017). https://doi.org/10.1021/acsami.7b01418160.
H. Lv, Z. Xi, Z. Chen, S. Guo, Y. Yu, W. Zhu, Q. Li, X. Zhang, M. Pan, and G.
Lu, “ A new core/shell NiAu/Au nanoparticle catalyst with Pt-like activity for
hydrogen evolution reaction,” J. Am. Chem. Soc. 137(18), 5859–5862 (2015).
https://doi.org/10.1021/jacs.5b01100161. A. Papaderakis, N. Pliatsikas, P.
Patsalas, D. Tsiplakides, S. Balomenou, A. Touni, and S. Sotiropoulos, “
Hydrogen evolution at Ir-Ni bimetallic deposits prepared by galvanic
replacement,” J. Electroanal. Chem. 808(1), 21–27 (2018).
https://doi.org/10.1016/j.jelechem.2017.11.055162. Y. Li, S. Chen, R. Long, H.
Ju, Z. Wang, X. Yu, F. Gao, Z. Cai, C. Wang, and Q. Xu, “ Near-surface dilution
of trace Pd atoms to facilitate Pd-H bond cleavage for giant enhancement of
electrocatalytic hydrogen evolution,” Nano Energy 34, 306–312 (2017).
https://doi.org/10.1016/j.nanoen.2017.02.048163. M. Bao, I. S. Amiinu, T. Peng,
W. Li, S. Liu, Z. Wang, Z. Pu, D. He, Y. Xiong, and S. Mu, “ Surface evolution
of PtCu alloy shell over Pd nanocrystals leads to superior hydrogen evolution
and oxygen reduction reactions,” ACS Energy Lett. 3(4), 940–945 (2018).
https://doi.org/10.1021/acsenergylett.8b00330 Typically, Lv et al. first adopted
the low-temperature solvothermal reduction to fabricate the alloyed NiAu
nanoparticles as the pre-catalyst, and then electrochemical cycling between 0.6
and 1.0 V was conducted to transform the NiAu alloy to a core–shell NiAu/Au
nanostructure.160160. H. Lv, Z. Xi, Z. Chen, S. Guo, Y. Yu, W. Zhu, Q. Li, X.
Zhang, M. Pan, and G. Lu, “ A new core/shell NiAu/Au nanoparticle catalyst with
Pt-like activity for hydrogen evolution reaction,” J. Am. Chem. Soc. 137(18),
5859–5862 (2015). https://doi.org/10.1021/jacs.5b01100 This designed core–shell
material exhibited much improved HER catalysis with a Pt-like activity and
highly strong robustness. Theoretical results showed that these low-coordination
Au sites around the shell were the main origin of the high activity. Such
strategy could also be extended to other Au-based alloys, such as CoAu and FeAu.
According to the study of Li et al., a selective etching-deposition route was
proposed to realize the implantation of trace Pd atoms into the near-surface
lattice of Ag nanocubes, so as to form a heteroatom-rich Pd–Ag shell on the
surface of Ag (Ag@PdAg).162162. Y. Li, S. Chen, R. Long, H. Ju, Z. Wang, X. Yu,
F. Gao, Z. Cai, C. Wang, and Q. Xu, “ Near-surface dilution of trace Pd atoms to
facilitate Pd-H bond cleavage for giant enhancement of electrocatalytic hydrogen
evolution,” Nano Energy 34, 306–312 (2017).
https://doi.org/10.1016/j.nanoen.2017.02.048 Such atomic dilution substantially
promoted electronic desorption of adsorbed H species. Consequently, the
catalytic activity for HER was considerably increased by ∼14 times of that of Pd
catalysts, along with a high endurance. Furthermore, a unique core–shell Pd@PtCu
dodecahedron nanostructure was also reported by Mu's group, which demonstrated
the extraordinary HER catalytic properties in acidic media.163163. M. Bao, I. S.
Amiinu, T. Peng, W. Li, S. Liu, Z. Wang, Z. Pu, D. He, Y. Xiong, and S. Mu, “
Surface evolution of PtCu alloy shell over Pd nanocrystals leads to superior
hydrogen evolution and oxygen reduction reactions,” ACS Energy Lett. 3(4),
940–945 (2018). https://doi.org/10.1021/acsenergylett.8b00330
In addition, a handful of simple bimetallic heterostructure composites (M/M)
without the core–shell structure were also synthesized for catalyzing
HER.164–166164. J. Fan, K. Qi, L. Zhang, H. Zhang, S. Yu, and X. Cui, “
Engineering Pt/Pd interfacial electronic structures for highly efficient
hydrogen evolution and alcohol oxidation,” ACS Appl. Mater. Interfaces 9(21),
18008–18014 (2017). https://doi.org/10.1021/acsami.7b05290165. U. Joshi, S.
Malkhandi, Y. Ren, T. L. Tan, S. Y. Chiam, and B. S. Yeo, “ Ruthenium-tungsten
composite catalyst for the efficient and contamination-resistant electrochemical
evolution of hydrogen,” ACS Appl. Mater. Interfaces 10(7), 6354–6360 (2018).
https://doi.org/10.1021/acsami.7b17970166. J. Ding, Q. Shao, Y. Feng, and X.
Huang, “ Ruthenium-nickel sandwiched nanoplates for efficient water splitting
electrocatalysis,” Nano Energy 47, 1–7 (2018).
https://doi.org/10.1016/j.nanoen.2018.02.017 For example, a Pd–Pt
heterostructure, composed of Pt nanoparticles grown on Pd (100) nanosheets,
could induce more free electrons transfer from Pd (100) to Pt, and thus recorded
a Pt-outperformed electrocatalytic activity in base.164164. J. Fan, K. Qi, L.
Zhang, H. Zhang, S. Yu, and X. Cui, “ Engineering Pt/Pd interfacial electronic
structures for highly efficient hydrogen evolution and alcohol oxidation,” ACS
Appl. Mater. Interfaces 9(21), 18008–18014 (2017).
https://doi.org/10.1021/acsami.7b05290 Besides, Joshi et al. physically mixed
the Ru and W powder as an efficient electrocatalyst and discovered that a
remarkable synergistical interaction was created in this mixture.165165. U.
Joshi, S. Malkhandi, Y. Ren, T. L. Tan, S. Y. Chiam, and B. S. Yeo, “
Ruthenium-tungsten composite catalyst for the efficient and
contamination-resistant electrochemical evolution of hydrogen,” ACS Appl. Mater.
Interfaces 10(7), 6354–6360 (2018). https://doi.org/10.1021/acsami.7b17970
Typically, the d-band of Ru was decreased and its electron work function was
increased, which were well supported by the calculation and experimental data.
As such, the hydrogen-binding energy of the surface Ru was tuned to approach
that of Pt(111), which in turn, led to the improvement of catalytic behavior. In
a 0.5 M H2SO4 electrolyte medium, the overpotential at the current density of 10
mA cm−2 was 85 mV, much less than those of individual Ru and W (∼165 and 465 mV,
respectively).
2. Hybridizing with stable metal compounds
According to extensive research, assembling NMNs with some stable metal
compounds (such as transition metal oxides, hydroxide, chalcogenides,
phosphides, nitrides, carbides, etc.) to form the heterostructured hybrids has
been demonstrated to effectively boost the HER electrocatalytic property, owing
to the chemical and electrical synergy between NMNs and other
compounds.79,167–18379. M. K. Kundu, R. Mishra, T. Bhowmik, and S. Barman, “
Rhodium metal-rhodium oxide (Rh-Rh2O3) nanostructures with Pt-like or better
activity towards hydrogen evolution and oxidation reactions (HER, HOR) in acid
and base: Correlating its HOR/HER activity with hydrogen binding energy and
oxophilicity of the catalyst,” J. Mater. Chem. A 6(46), 23531–23541 (2018).
https://doi.org/10.1039/C8TA07028H167. Y. Zhang, J. Shi, G. Han, M. Li, Q. Ji,
D. Ma, Y. Zhang, C. Li, X. Lang, and Y. Zhang, “ Chemical vapor deposition of
monolayer WS2 nanosheets on Au foils toward direct application in hydrogen
evolution,” Nano Res. 8(9), 2881–2890 (2015).
https://doi.org/10.1007/s12274-015-0793-z168. S. Zhao, R. Jin, Y. Song, H.
Zhang, S. D. House, J. C. Yang, and R. Jin, “ Atomically precise gold
nanoclusters accelerate hydrogen evolution over MoS2 nanosheets: The dual
interfacial effect,” Small 13(43), 1701519 (2017).
https://doi.org/10.1002/smll.201701519169. K. Zhou, Q. Zhang, Z. Wang, C. Wang,
C. Han, X. Ke, Z. Zheng, H. Wang, J. Liu, and H. Yan, “ A
Setaria-inflorescence-structured catalyst based on nickel-cobalt wrapped silver
nanowire conductive networks for highly efficient hydrogen evolution,” J. Mater.
Chem. A 7(46), 26566–26573 (2019). https://doi.org/10.1039/C9TA10413E170. X.
Ding, Y. Xia, Q. Li, S. Dong, X. Jiao, and D. Chen, “ Interface engineering of
Co(OH)2/Ag/FeP hierarchical superstructure as efficient and robust
electrocatalyst for overall water splitting,” ACS Appl. Mater. Interfaces 11(8),
7936–7945 (2019). https://doi.org/10.1021/acsami.8b19623171. J. Joo, H. Jin, A.
Oh, B. Kim, J. Lee, H. Baik, S. H. Joo, and K. Lee, “ An IrRu alloy nanocactus
on Cu2-xS@IrSy as a highly efficient bifunctional electrocatalyst toward overall
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Ru decorated with NiCoP: An efficient and durable hydrogen evolution reaction
electrocatalyst in both acidic and alkaline conditions,” Chem. Commun. 53(98),
13153–13156 (2017). https://doi.org/10.1039/C7CC08340H176. D. Yoon, J. Lee, B.
Seo, B. Kim, H. Baik, S. H. Joo, and K. Lee, “ Cactus-like hollow Cu2-x S@Ru
nanoplates as excellent and robust electrocatalysts for the alkaline hydrogen
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Li, and Y. Chen, “ Inlay of ultrafine Ru nanoparticles into a self-supported
Ni(OH)2 nanoarray for hydrogen evolution with low overpotential and enhanced
kinetics,” J. Mater. Chem. A 7(18), 11062–11068 (2019).
https://doi.org/10.1039/C9TA02451D178. J. Xu, T. Liu, J. Li, B. Li, Y. Liu, B.
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phosphide,” Energy Environ. Sci. 11(7), 1819–1827 (2018).
https://doi.org/10.1039/C7EE03603E179. Y. Liu, S. Liu, Y. Wang, Q. Zhang, L. Gu,
S. Zhao, D. Xu, Y. Li, J. Bao, and Z. Dai, “ Ru modulation effects in the
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NPC@RuO2 synthesized via environment-friendly and solid-phase phosphating
process by saccharomycetes as N/P sources and carbon template for overall water
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Han, J. Bao, and Z. Dai, “ Amorphous Y(OH)3-promoted Ru/Y(OH)3 nanohybrids with
high durability for electrocatalytic hydrogen evolution in alkaline media,”
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L. Wang, Q. Zhou, Z. Pu, Q. Zhang, X. Mu, H. Jing, S. Liu, C. Chen, and S. Mu, “
Surface reconstruction engineering of cobalt phosphides by Ru inducement to form
hollow Ru-RuPx-CoxP pre-electrocatalysts with accelerated oxygen evolution
reaction,” Nano Energy 53, 270–276 (2018).
https://doi.org/10.1016/j.nanoen.2018.08.061183. Z. Liu, Z. Li, J. Li, J. Xiong,
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hydrogen evolution reaction,” J. Mater. Chem. A 7(10), 5621–5625 (2019).
https://doi.org/10.1039/C8TA11635K Also, the good cost-competitiveness is
balanced from a lowered amount of noble metals. Among a plethora of metal
compounds, the 2D layered metal dichalcogenides, typically MoS2, as the host
material for hybridizing with noble metals are well documented.184–194184. Y.
Shi, J. Wang, C. Wang, T.-T. Zhai, W.-J. Bao, J.-J. Xu, X.-H. Xia, and H.-Y.
Chen, “ Hot electron of Au nanorods activates the electrocatalysis of hydrogen
evolution on MoS2 nanosheets,” J. Am. Chem. Soc. 137(23), 7365–7370 (2015).
https://doi.org/10.1021/jacs.5b01732185. J. Zhang, T. Wang, L. Liu, K. Du, W.
Liu, Z. Zhu, and M. Li, “ Molybdenum disulfide and Au ultrasmall nanohybrids as
highly active electrocatalysts for hydrogen evolution reaction,” J. Mater. Chem.
A 5(8), 4122–4128 (2017). https://doi.org/10.1039/C6TA10385E186. Y. Li, M. B.
Majewski, S. M. Islam, S. Hao, A. A. Murthy, J. G. DiStefano, E. D. Hanson, Y.
Xu, C. Wolverton, and M. G. Kanatzidis, “ Morphological engineering of winged
Au@MoS2 heterostructures for electrocatalytic hydrogen evolution,” Nano Lett.
18(11), 7104–7110 (2018). https://doi.org/10.1021/acs.nanolett.8b03109187. B.
Shang, X. Cui, L. Jiao, K. Qi, Y. Wang, J. Fan, Y. Yue, H. Wang, Q. Bao, and X.
Fan, “ Lattice-mismatch-induced ultrastable 1T-phase MoS2-Pd/Au for
plasmon-enhanced hydrogen evolution,” Nano Lett. 19(5), 2758–2764 (2019).
https://doi.org/10.1021/acs.nanolett.8b04104188. Z. Liu, X. Zhang, Y. Gong, Q.
Lu, Z. Zhang, H. Cheng, Q. Ma, J. Chen, M. Zhao, and B. Chen, “ Synthesis of
MoX2 (X = Se or S) monolayers with high-concentration 1T′ phase on 4H/fcc-Au
nanorods for hydrogen evolution,” Nano Res. 12(6), 1301–1305 (2019).
https://doi.org/10.1007/s12274-018-2212-8189. F. Scaglione, Y. Xue, F. Celegato,
P. Rizzi, and L. Battezzati, “ Amorphous molybdenum sulphide@nanoporous gold as
catalyst for hydrogen evolution reaction in acidic environment,” J. Mater. Sci.
53(17), 12388–12398 (2018). https://doi.org/10.1007/s10853-018-2490-2190. S.
Wei, X. Cui, Y. Xu, B. Shang, Q. Zhang, L. Gu, X. Fan, L. Zheng, C. Hou, and H.
Huang, “ Iridium-triggered phase transition of MoS2 nanosheets boosts overall
water splitting in alkaline media,” ACS Energy Lett. 4(1), 368–374 (2019).
https://doi.org/10.1021/acsenergylett.8b01840191. S. Liu, M. Li, C. Wang, P.
Jiang, L. Hu, and Q. Chen, “ Tuning the electronic structure of Se via
constructing Rh-MoSe2 nanocomposite to generate high-performance
electrocatalysis for hydrogen evolution reaction,” ACS Sustainable Chem. Eng.
6(7), 9137–9144 (2018). https://doi.org/10.1021/acssuschemeng.8b01467192. Y.
Cheng, S. Lu, F. Liao, L. Liu, Y. Li, and M. Shao, “ Rh-MoS2 nanocomposite
catalysts with Pt-like activity for hydrogen evolution reaction,” Adv. Funct.
Mater. 27(23), 1700359 (2017). https://doi.org/10.1002/adfm.201700359193. M. D.
Sharma, C. Mahala, and M. Basu, “ Nanosheets of MoSe2@ M (M = Pd and Rh)
function as widespread pH tolerable hydrogen evolution catalyst,” J. Colloid
Interface Sci. 534(15), 131–141 (2019).
https://doi.org/10.1016/j.jcis.2018.09.018194. J. Liu, Y. Zheng, D. Zhu, A.
Vasileff, T. Ling, and S.-Z. Qiao, “ Identification of pH-dependent synergy on
Ru/MoS2 interface: A comparison of alkaline and acidic hydrogen evolution,”
Nanoscale 9(43), 16616–16621 (2017). https://doi.org/10.1039/C7NR06111K
Previously in 2015, a seminal study highlighted that Au metal localized surface
plasmon resonance could activate the HER activity of MoS2, with a about
threefold improvement in the current density.184184. Y. Shi, J. Wang, C. Wang,
T.-T. Zhai, W.-J. Bao, J.-J. Xu, X.-H. Xia, and H.-Y. Chen, “ Hot electron of Au
nanorods activates the electrocatalysis of hydrogen evolution on MoS2
nanosheets,” J. Am. Chem. Soc. 137(23), 7365–7370 (2015).
https://doi.org/10.1021/jacs.5b01732 In this case, a hybrid of Au nanorods
assembled onto exfoliated MoS2 nanosheets (Au–MoS2) was constructed, in which Au
metal was identified as a light absorber to excite electron–hole pair while MoS2
nanosheets acted as the electron acceptor and active centers to promote hydrogen
production. Accordingly, the charge density of MoS2 nanosheets was substantially
increased, which in turn, modulated the energy level of this material more
suitable for HER. Afterwards, following the metal-seeding principle, Li and his
co-workers witnessed a unique design of vertically aligned and winged MoS2
nanolayer surrounding the Au nanoarchitectures (w-Au@MoS2), which resulted in
the generation of plentiful edge-terminated active sites for driving hydrogen
production, and simultaneously offered a low-resistance electron transport
pathway within the w-Au@MoS2 nanostructures through the mediation of the Au
core.186186. Y. Li, M. B. Majewski, S. M. Islam, S. Hao, A. A. Murthy, J. G.
DiStefano, E. D. Hanson, Y. Xu, C. Wolverton, and M. G. Kanatzidis, “
Morphological engineering of winged Au@MoS2 heterostructures for
electrocatalytic hydrogen evolution,” Nano Lett. 18(11), 7104–7110 (2018).
https://doi.org/10.1021/acs.nanolett.8b03109 Therefore, an enhanced and
high-efficiency hydrogen evolution process in an acidic electrolyte was
realized. Furthermore, in the last year, Zheng's group integrated ultrasmall Ir
species with 2H-MoS2, namely, Ir/MoS2 heterostructures, through a simple
two-step solvothermal method, and found an interesting phase transformation from
2H to 1T of MoS2.190190. S. Wei, X. Cui, Y. Xu, B. Shang, Q. Zhang, L. Gu, X.
Fan, L. Zheng, C. Hou, and H. Huang, “ Iridium-triggered phase transition of
MoS2 nanosheets boosts overall water splitting in alkaline media,” ACS Energy
Lett. 4(1), 368–374 (2019). https://doi.org/10.1021/acsenergylett.8b01840 During
the synthesis, (NH4)6Mo7O24·4H2O, and thiourea were first uniformly dissolved in
water with the aid of stirring, and was heated at 220 °C for 18 h in a stainless
steel autoclave. Subsequently, the as-obtained MoS2 nanosheets were dispersed
into ethylene glycol under ultrasonic treatment with adding a certain amount of
H2IrCl6, and then the system was heated at 160 °C for 3 h. Thus, the Ir/MoS2
heterostructures were produced. The coupling of the computational and
experimental data stated that such phase transition was caused by the strong
interaction between the MoS2 support and Ir metal. From the HAADF-STEM images in
Figs. 20(a)–20(e), it was shown that the as-formed 1T phase was present in these
regions of MoS2 surrounded by Ir nanoparticles. When applied as the
electrocatalysts for HER and OER in alkaline solution, it only took the Ir/MoS2
heterostructure a low overpotential of 44 and 330 mV, respectively, to reach a
10 mA cm−2 current density, and a Tafel slope of 32 and 44 mV dec−1,
respectively, superior to these data of the benchmark Pt/C and IrO2 [Figs.
20(f)–20(i)]. Besides, a two-electrode water electrolyzer with the Ir/MoS2
heterostructure as electrocatalysts offered a high performance, with a cell
potential of only 1.57 V at the current density of 10 mA cm−2 [Fig. 20(j)]. The
outstanding catalytic behavior of this material could be correlated to several
aspects, i.e., enhanced electrical conductivity from 1T phase, better
hydrophilicity and more active centers derived from numerous heterojunction
interfaces, along with the synergy-promoted reaction kinetics.
FIG. 20. (a) HAADF-STEM image and (b) and (d) the corresponding magnified one of
the (c) and (d) areas in (a). (c) and (e) Filtered enlarged images of the marked
parts in (b) and (d). (f) LSV curves and (g) corresponding Tafel plots of the
Ir/MoS2 heterostructure, MoS2, commercial Ir/C, and Pt/C for the HER in 1 M KOH.
(h) OER polarization curves and (i) the corresponding Tafel plots of the Ir/MoS2
heterostructure, MoS2, commercial IrO2 in 1 M KOH. (j) The overall
water-splitting activity of Ir/MoS2–Ir/MoS2 and commercial IrO2–Pt/C in 1 M KOH.
Reproduced with permission from Wei et al., ACS Energy Lett. 4(1), 368–374
(2018). Copyright 2018 American Chemical Society.
* PPT
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* High-resolution
Similarly, around the same time, a composite catalyst consisting of a bimetallic
nanostructure (single-side-nucleated Au nanoislands with Pd nanosheets)
co-assembled on the 2H-MoS2 surface was developed to also create the stable
1T-phase-dominated MoS2 at the contacted area and manifested a dramatic
improvement of catalytic activity for the HER under acidic conditions.187187. B.
Shang, X. Cui, L. Jiao, K. Qi, Y. Wang, J. Fan, Y. Yue, H. Wang, Q. Bao, and X.
Fan, “ Lattice-mismatch-induced ultrastable 1T-phase MoS2-Pd/Au for
plasmon-enhanced hydrogen evolution,” Nano Lett. 19(5), 2758–2764 (2019).
https://doi.org/10.1021/acs.nanolett.8b04104 DFT results pointed out that
lattice-mismatch-induced compressive strain evoked such a phase transition. As
to the Rh-MoS2 nanocomposite with a small amount of Rh (ca. 5.2%), driven by the
H spillover from Rh to MoS2, the hybrid material paralleled the satisfactory HER
catalytic activity of the commercial Pt/C in acid.192192. Y. Cheng, S. Lu, F.
Liao, L. Liu, Y. Li, and M. Shao, “ Rh-MoS2 nanocomposite catalysts with Pt-like
activity for hydrogen evolution reaction,” Adv. Funct. Mater. 27(23), 1700359
(2017). https://doi.org/10.1002/adfm.201700359 In Yang's group, the exploited
nanocomposite of single Ru atoms adhered to MoS2 nanosheets on a carbon cloth
substrate also had an attractive HER activity with the η10 values of 41, 61, and
114 mV in different electrolytes (1M KOH, 0.5 M H2SO4, and 1 M PBS,
respectively.).195195. D. Wang, Q. Li, C. Han, Z. Xing, and X. Yang, “
Single-atom ruthenium based catalyst for enhanced hydrogen evolution,” Appl.
Catal. B 249(15), 91–97 (2019). https://doi.org/10.1016/j.apcatb.2019.02.059
Such a nanostructure was revealed to contain a great deal of atomic Ru active
sites, increased electrical conductivity and 3D porous architecture for rapid
mass transfer, as well as a synergistic electron interplay, thus propelling its
activity remarkably.
Regarding other metal compounds, various typical examples are also listed below.
The strongly coupled Mo2N–Au nanostructure displayed an electrocatalytic
performance for the HER approaching to that of commercial Pt/C.196196. A.
Morozan, V. Goellner, A. Zitolo, E. Fonda, B. Donnadieu, D. Jones, and F.
Jaouen, “ Synergy between molybdenum nitride and gold leading to platinum-like
activity for hydrogen evolution,” Phys. Chem. Chem. Phys. 17(6), 4047–4053
(2015). https://doi.org/10.1039/C4CP04358H Pd nanoparticles sized ca. 3 nm
firmly supported on flowerlike NiCo2S4 hollow sub-microspheres also presented
low overpotentials of 83 and 87 mV to yield a 10 mA cm−2 current density toward
the HER in 1 M KOH and 0.5 M H2SO4, while those for either Pd or NiCo2S4 were
much larger.197197. G. Sheng, J. Chen, Y. Li, H. Ye, Z. Hu, X.-Z. Fu, R. Sun, W.
Huang, and C.-P. Wong, “ Flowerlike NiCo2S4 hollow sub-microspheres with
mesoporous nanoshells support Pd nanoparticles for enhanced hydrogen evolution
reaction electrocatalysis in both acidic and alkaline conditions,” ACS Appl.
Mater. Interfaces 10(26), 22248–22256 (2018).
https://doi.org/10.1021/acsami.8b05427 Recently, Song and his co-workers
fabricated Ag nanodots decorated the porous Cu2O nanobelts network on the Cu
foam (Ag@Cu2O/CF) by the simple in situ growth in a mixed solution at room
temperature [Fig. 21(a)].198198. C. Song, Z. Zhao, X. Sun, Y. Zhou, Y. Wang, and
D. Wang, “ In situ growth of Ag nanodots decorated Cu2O porous nanobelts
networks on copper foam for efficient HER electrocatalysis,” Small 15(29),
1804268 (2019). https://doi.org/10.1002/smll.201804268 Such Ag@Cu2O/CF
maneuvered a substantially boosted HER catalytic behavior, specifically with a
η10 of 108 mV, a Tafel slope of 58 mV dec−1, as well as excellent durability for
over 20 h in alkaline media [Figs. 21(b)–21(d)]. This enhancement of performance
was originated from the 3D porous nanoarchitecture that provided an abundance of
Ag active centers, enabling an effective utilization of Ag metal and offering
rapid charge/mass transportation pathway in catalyzing the HER, and more
significantly the strong synergistic interaction between different parts, which
tuned the H adsorption–desorption rate to reach a more suitable value [Fig.
21(e)]. Likewise, Ag nanoparticles were coupled with tungsten oxide (WO3) to
create a heteroarchitecture (denoted as Ag–WO3).199199. J. Ma, Z. Ma, B. Liu, S.
Wang, R. Ma, and C. Wang, “ Composition of Ag-WO3 core-shell nanostructures as
efficient electrocatalysts for hydrogen evolution reaction,” J. Solid State
Chem. 271, 246–252 (2019). https://doi.org/10.1016/j.jssc.2018.12.020 The
resultant intimate interplay between Ag and WO3 also recorded an excellent
catalytic activity for the HER in acidic electrolytes. In another recent study,
Yao et al. controllably deposited Pt submonolayer on Pd3Pb nanoplates, namely,
AL–Pt/Pd3Pb. Such a heterojunction structure greatly optimized the electronic
structure and atomic utilization efficiency of the active Pt atomic layer,
thereby markedly improving the HER performance in acid.200200. Y. Yao, X.-K. Gu,
D. He, Z. Li, W. Liu, Q. Xu, T. Yao, Y. Lin, H.-J. Wang, and C. Zhao, “
Engineering the electronic structure of submonolayer Pt on intermetallic Pd3Pb
via charge transfer boosts the hydrogen evolution reaction,” J. Am. Chem. Soc.
141(51), 19964–19968 (2019). https://doi.org/10.1021/jacs.9b09391 Compared to
commercial Pt/C, the overpotential at 10 mA cm−2 for AL–Pt/Pd3Pb was lowered by
∼16 mV (30 mV for Pt/C vs 13.8 mV for AL-Pt/Pd3Pb) and its corresponding mass
activity at the overpotential of 50 mV was increased by four times (1486 A/gPt
for Pt/C vs 7834 A/gPd+Pt for AL–Pt/Pd3Pb). DFT calculation results disclosed
that a strong electrostatic interaction was created due to the electron transfer
from Pd3Pb to Pt, which could make the transition state stabilized and decrease
the reaction barrier, so as to afford the enhanced activity [Figs. 21(f)–21(j)].
FIG. 21. (a) The synthesis route of the Ag@Cu2O/CF hybrid. (b) HER polarization
curves and (c) Tafel plots of different electrocatalysts in the alkaline
solution. (d) Long-term durability test of this Ag@Cu2O/CF composite. (e) The
H-adsorption free energy of different materials. Reproduced with permission from
Song et al., Small 15(29), 1804268 (2019). Copyright 2019 Wiley-VCH. (f) and (g)
Charge density distribution model of the Pt/Pd3Pb hybrid. Transition states for
the (h) Volmer and (i) Heyrovsky steps on the surface of Pt/Pd3Pb. (j) The
calculated reaction barriers for different steps. Reproduced with permission
from Yao et al., J. Am. Chem. Soc. 141(51), 19964–19968 (2019). Copyright 2019
American Chemical Society.
* PPT
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* High-resolution
A hydroxide–metal–hydroxide composite system consisting of Co(OH)2, Au, and
Ni(OH)2 has also been produced by Sultana and his co-workers to form
multiheterogeneous Co(OH)2–Au–Ni(OH)2 nanosheets.201201. U. K. Sultana, J. D.
Riches, and A. P. O'Mullane, “ Gold doping in a layered Co-Ni hydroxide system
via galvanic replacement for overall electrochemical water splitting,” Adv.
Funct. Mater. 28(43), 1804361 (2018). https://doi.org/10.1002/adfm.201804361
During the synthesis, highly distributed Au with a very low concentration was
first attained through the galvanic replacement of Co(OH)2, and then the
as-formed Au directed the electrodeposition of Ni(OH)2, enabling it homogeneous
distribution on the surface. Notably, via adjusting the Au amount from 0.1 to
0.2 at. %, this composite material showed optimal activity toward the HER and
OER. Moreover, it was found that in both cases Au was no longer confined to the
middle of the material, but was redistributed throughout the composite sample on
basis of electrochemical activation operation, which activated the overall
catalysis process.
3. Integrating with conductive substrates
To further optimize the catalytic behavior of noble-metal materials under the
HER conditions, integrating NM-based materials with some relatively conductive
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https://doi.org/10.1038/ncomms12272213. B. Jiang, L. Yang, F. Liao, M. Sheng, H.
Zhao, H. Lin, and M. Shao, “ A stepwise-designed Rh-Au-Si nanocomposite that
surpasses Pt/C hydrogen evolution activity at high overpotentials,” Nano Res.
10(5), 1749–1755 (2017). https://doi.org/10.1007/s12274-017-1447-0214. M. Sheng,
B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y. Lifshitz, S.-T. Lee, and M.
Shao, “ Approaching the volcano top: Iridium/silicon nanocomposites as efficient
electrocatalysts for the hydrogen evolution reaction,” ACS Nano 13(3), 2786–2794
(2019). https://doi.org/10.1021/acsnano.8b07572215. V. Pérez-Herranz, R. Medina,
P. Taymans, C. González-Buch, E. Ortega, G. Sánchez-Loredo, and G. J.
Labrada-Delgado, “ Modification of porous nickel electrodes with silver
nanoparticles for hydrogen production,” J. Electroanal. Chem. 808(1), 420–426
(2018). https://doi.org/10.1016/j.jelechem.2017.06.022216. Y. Liang, C.
Csoklich, D. McLaughlin, O. Schneider, and A. S. Bandarenka, “ Revealing active
sites for hydrogen evolution at Pt and Pd atomic layers on Au surfaces,” ACS
Appl. Mater. Interfaces 11(13), 12476–12480 (2019).
https://doi.org/10.1021/acsami.8b22146 Here, this robust conjugation between
active noble-metal phases and conductive supports not only addresses the
limitations of electric conductivity, but also shrinks the particle size and
increases the dispersity of the metal particles along with reducing their
dosage. Moreover, the strong synergistic effects can also take place between the
two constituents, which will modulate the electronic structure, accelerate the
charge transfer of them, and amend the hydrogen adsorption/desorption behavior,
thereby promoting the hydrogen production.
a. Carbon-related supports
As for carbon supports, some representative merits, such as the superior
conductivity, well-developed pore architecture, controllable molecular
structure, strong resistance to chemical attack, etc., make them hold a great
promise as the matrixes. Up to now, plentiful composites of various nanocarbon
supports with noble metal-based nanomaterials have been established, such as Pd
NPs@N-carbon nanotubes (CNTs), Ru@ self-crosslinking (SC)-carbon quantum dots
(CQDs), Au@NC, etc.37,60,217–23137. Y. Qin, X. Dai, X. Zhang, X. Huang, H. Sun,
D. Gao, Y. Yu, P. Zhang, Y. Jiang, and H. Zhuo, “ Microwave-assisted synthesis
of multiply-twinned Au-Ag nanocrystals on reduced graphene oxide for high
catalytic performance towards hydrogen evolution reaction,” J. Mater. Chem. A
4(10), 3865–3871 (2016). https://doi.org/10.1039/C5TA10428A60. J. Wang, H. Zhu,
D. Yu, J. Chen, J. Chen, M. Zhang, L. Wang, and M. Du, “ Engineering the
composition and structure of bimetallic Au-Cu alloy nanoparticles in carbon
nanofibers: Self-supported electrode materials for electrocatalytic water
splitting,” ACS Appl. Mater. Interfaces 9(23), 19756–19765 (2017).
https://doi.org/10.1021/acsami.7b01418217. W. Zhou, T. Xiong, C. Shi, J. Zhou,
K. Zhou, N. Zhu, L. Li, Z. Tang, and S. Chen, “ Bioreduction of precious metals
by microorganism: Efficient Gold@N-doped carbon electrocatalysts for the
hydrogen evolution reaction,” Angew. Chem., Int. Ed. 55(29), 8416–8420 (2016).
https://doi.org/10.1002/anie.201602627218. J. Zhang, G. Wang, Z. Liao, P. Zhang,
F. Wang, X. Zhuang, E. Zschech, and X. Feng, “ Iridium nanoparticles anchored on
3D graphite foam as a bifunctional electrocatalyst for excellent overall water
splitting in acidic solution,” Nano Energy 40, 27–33 (2017).
https://doi.org/10.1016/j.nanoen.2017.07.054219. J. Mahmood, M. A. R. Anjum, S.
H. Shin, I. Ahmad, H. J. Noh, S. J. Kim, H. Y. Jeong, J. S. Lee, and J. B. Baek,
“ Encapsulating iridium nanoparticles inside a 3D cage-like organic network as
an efficient and durable catalyst for the hydrogen evolution reaction,” Adv.
Mater. 30(52), 1805606 (2018). https://doi.org/10.1002/adma.201805606220. H.
Wang, M. Ming, M. Hu, C. Xu, Y. Wang, Y. Zhang, D. Gao, J. Bi, G. Fan, and J.-S.
Hu, “ Size and electronic modulation of iridium nanoparticles on
nitrogen-functionalized carbon toward advanced electrocatalysts for alkaline
water splitting,” ACS Appl. Mater. Interfaces 10(26), 22340–22347 (2018).
https://doi.org/10.1021/acsami.8b07639221. S. B. Roy, K. Akbar, J. H. Jeon,
S.-K. Jerng, L. Truong, K. Kim, Y. Yi, and S.-H. Chun, “ Iridium on vertical
graphene as an all-round catalyst for robust water splitting reactions,” J.
Mater. Chem. A 7(36), 20590–20596 (2019). https://doi.org/10.1039/C9TA07388D222.
S. Zhou, X. Chen, P. Yu, F. Gao, and L. Mao, “ Nitrogen-doped carbon nanotubes
as an excellent substrate for electroless deposition of Pd nanoparticles with a
high efficiency toward the hydrogen evolution reaction,” Electrochem. Commun.
90, 91–95 (2018). https://doi.org/10.1016/j.elecom.2018.04.015223. H. Yu, Y.
Xue, B. Huang, L. Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “
Ultrathin nanosheet of graphdiyne-supported palladium atom catalyst for
efficient hydrogen production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006224. K. Guo, L. J. Rowland, L. H.
Isherwood, G. Glodan, and A. Baidak, “ Photon-induced synthesis of ultrafine
metal nanoparticles on graphene as electrocatalysts: Impact of functionalization
and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B225. J. Bai, S.-H. Xing, Y.-Y. Zhu, J.-X.
Jiang, J.-H. Zeng, and Y. Chen, “ Polyallylamine-Rh nanosheet
nanoassemblies-carbon nanotubes organic-inorganic nanohybrids: A electrocatalyst
superior to Pt for the hydrogen evolution reaction,” J. Power Sources 385(1),
32–38 (2018). https://doi.org/10.1016/j.jpowsour.2018.03.022226. W. Shen, L. Ge,
Y. Sun, F. Liao, L. Xu, Q. Dang, Z. Kang, and M. Shao, “ Rhodium
nanoparticles/F-doped graphene composites as multifunctional electrocatalyst
superior to Pt/C for hydrogen evolution and formic acid oxidation reaction,” ACS
Appl. Mater. Interfaces 10(39), 33153–33161 (2018).
https://doi.org/10.1021/acsami.8b09297227. L. Bai, Z. Duan, X. Wen, R. Si, Q.
Zhang, and J. Guan, “ Highly dispersed ruthenium-based multifunctional
electrocatalyst,” ACS Catal. 9(11), 9897–9904 (2019).
https://doi.org/10.1021/acscatal.9b03514228. M. Li, H. Wang, W. Zhu, W. Li, C.
Wang, and X. Lu, “ RuNi nanoparticles embedded in N-doped carbon nanofibers as a
robust bifunctional catalyst for efficient overall water splitting,” Adv. Sci.
7(2), 1901833 (2020). https://doi.org/10.1002/advs.201901833229. Y. Liu, Y.
Yang, Z. Peng, Z. Liu, Z. Chen, L. Shang, S. Lu, and T. Zhang, “
Self-crosslinking carbon dots loaded ruthenium dots as an efficient and
super-stable hydrogen production electrocatalyst at all pH values,” Nano Energy
65, 104023 (2019). https://doi.org/10.1016/j.nanoen.2019.104023230. T. Bhowmik,
M. K. Kundu, and S. Barman, “ Palladium nanoparticle-graphitic carbon nitride
porous synergistic catalyst for hydrogen evolution/oxidation reactions over a
broad range of pH and correlation of its catalytic activity with measured
hydrogen binding energy,” ACS Catal. 6(3), 1929–1941 (2016).
https://doi.org/10.1021/acscatal.5b02485231. T. Bhowmik, M. K. Kundu, and S.
Barman, “ Growth of one-dimensional RuO2 nanowires on g-carbon nitride: An
active and stable bifunctional electrocatalyst for hydrogen and oxygen evolution
reactions at all pH values,” ACS Appl. Mater. Interfaces 8(42), 28678–28688
(2016). https://doi.org/10.1021/acsami.6b10436
Graphenes (G)/reduced graphene oxides (rGO) and carbon nanotubes (CNTs) are
versatile candidates to support the noble metal-based particles for the
HER.37,221–22737. Y. Qin, X. Dai, X. Zhang, X. Huang, H. Sun, D. Gao, Y. Yu, P.
Zhang, Y. Jiang, and H. Zhuo, “ Microwave-assisted synthesis of multiply-twinned
Au-Ag nanocrystals on reduced graphene oxide for high catalytic performance
towards hydrogen evolution reaction,” J. Mater. Chem. A 4(10), 3865–3871 (2016).
https://doi.org/10.1039/C5TA10428A221. S. B. Roy, K. Akbar, J. H. Jeon, S.-K.
Jerng, L. Truong, K. Kim, Y. Yi, and S.-H. Chun, “ Iridium on vertical graphene
as an all-round catalyst for robust water splitting reactions,” J. Mater. Chem.
A 7(36), 20590–20596 (2019). https://doi.org/10.1039/C9TA07388D222. S. Zhou, X.
Chen, P. Yu, F. Gao, and L. Mao, “ Nitrogen-doped carbon nanotubes as an
excellent substrate for electroless deposition of Pd nanoparticles with a high
efficiency toward the hydrogen evolution reaction,” Electrochem. Commun. 90,
91–95 (2018). https://doi.org/10.1016/j.elecom.2018.04.015223. H. Yu, Y. Xue, B.
Huang, L. Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “
Ultrathin nanosheet of graphdiyne-supported palladium atom catalyst for
efficient hydrogen production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006224. K. Guo, L. J. Rowland, L. H.
Isherwood, G. Glodan, and A. Baidak, “ Photon-induced synthesis of ultrafine
metal nanoparticles on graphene as electrocatalysts: Impact of functionalization
and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B225. J. Bai, S.-H. Xing, Y.-Y. Zhu, J.-X.
Jiang, J.-H. Zeng, and Y. Chen, “ Polyallylamine-Rh nanosheet
nanoassemblies-carbon nanotubes organic-inorganic nanohybrids: A electrocatalyst
superior to Pt for the hydrogen evolution reaction,” J. Power Sources 385(1),
32–38 (2018). https://doi.org/10.1016/j.jpowsour.2018.03.022226. W. Shen, L. Ge,
Y. Sun, F. Liao, L. Xu, Q. Dang, Z. Kang, and M. Shao, “ Rhodium
nanoparticles/F-doped graphene composites as multifunctional electrocatalyst
superior to Pt/C for hydrogen evolution and formic acid oxidation reaction,” ACS
Appl. Mater. Interfaces 10(39), 33153–33161 (2018).
https://doi.org/10.1021/acsami.8b09297227. L. Bai, Z. Duan, X. Wen, R. Si, Q.
Zhang, and J. Guan, “ Highly dispersed ruthenium-based multifunctional
electrocatalyst,” ACS Catal. 9(11), 9897–9904 (2019).
https://doi.org/10.1021/acscatal.9b03514 For instance, Au–Ag nanocrystals with
the multiply twinned structure directly grown on rGO hybrids (Au–Ag NC/rGO) were
created by a facile microwave irradiation process.3737. Y. Qin, X. Dai, X.
Zhang, X. Huang, H. Sun, D. Gao, Y. Yu, P. Zhang, Y. Jiang, and H. Zhuo, “
Microwave-assisted synthesis of multiply-twinned Au-Ag nanocrystals on reduced
graphene oxide for high catalytic performance towards hydrogen evolution
reaction,” J. Mater. Chem. A 4(10), 3865–3871 (2016).
https://doi.org/10.1039/C5TA10428A The as-prepared Au–Ag NC/rGO displayed
outstanding HER electrocatalytic activity and stability, characterized by small
overpotentials and Tafel slopes, which was comparable to the commercial Pt/C.
The high HER performance was related to abundant twin defects and the intimate
electronic coupling between Au–Ag alloys and rGO. Recently, the hybrid Ir_VG (Ir
on vertical graphene) developed by Roy et al. manifested remarkable catalytic
peculiarities toward all-round water-splitting reactions (HER and OER in both
the acid and base).221221. S. B. Roy, K. Akbar, J. H. Jeon, S.-K. Jerng, L.
Truong, K. Kim, Y. Yi, and S.-H. Chun, “ Iridium on vertical graphene as an
all-round catalyst for robust water splitting reactions,” J. Mater. Chem. A
7(36), 20590–20596 (2019). https://doi.org/10.1039/C9TA07388D The resultant
sample was produced through the novel e-beam evaporation technique with the
minimal Ir mass loading, i.e., 50 μg cm−2. Under acid and alkaline conditions,
the Ir_VG showed the low η10 overpotentials (47 and 17 mV for HER, respectively;
300 and 320 mV for OER, respectively) and favorable Tafel slopes (43 and 29 mV
dec−1 for the HER, respectively; 59 and 53 mV dec−1 for the OER, respectively),
as well as excellent robustness. Similar to the aforementioned analysis, the
highly active Ir species, the excellently conductive and superaerophobic VG, and
the strong binding between them synergistically favored the overall catalytic
process. For CNT substrates, Pd nanoparticle (Pd NP) hybridized N-doped CNTs
were prepared by the electroless deposition of the K2PdCl4 solution.222222. S.
Zhou, X. Chen, P. Yu, F. Gao, and L. Mao, “ Nitrogen-doped carbon nanotubes as
an excellent substrate for electroless deposition of Pd nanoparticles with a
high efficiency toward the hydrogen evolution reaction,” Electrochem. Commun.
90, 91–95 (2018). https://doi.org/10.1016/j.elecom.2018.04.015 At the
overpotential of 100 mV, a current density of 32 mA cm−2 was reached for the Pd
NP@N–CNT hybrid. Besides, polyallylamine-functionalized Rh nanosheet
nanoassemblies supported on CNTs (PAH@Rh-NSNS/CNTs) were proposed by Bai and his
co-workers.225225. J. Bai, S.-H. Xing, Y.-Y. Zhu, J.-X. Jiang, J.-H. Zeng, and
Y. Chen, “ Polyallylamine-Rh nanosheet nanoassemblies-carbon nanotubes
organic-inorganic nanohybrids: A electrocatalyst superior to Pt for the hydrogen
evolution reaction,” J. Power Sources 385(1), 32–38 (2018).
https://doi.org/10.1016/j.jpowsour.2018.03.022 Benefiting from the ultrathin
morphology of 2D Rh nanosheets and 3D CNT networks, the PAH@Rh-NSNS/CNT
nanohybrid functioned well as a HER electrocatalyst in acidic media. The
observed overpotential at 10 mA cm−2 was just 5 mV, which was much better than
that of commercial platinum nanocrystals.
Additionally, several other well-known carbon nanomaterials, such as XC-72
Vulcan carbon, Ketjenblack, graphite, carbon quantum dots (CQDs), and so forth,
were often engaged as ideal conducting substrates to hybridize noble-metal
nanomaterials.49,50,127,128,229,23249. Y. Liu, X. Li, Q. Zhang, W. Li, Y. Xie,
H. Liu, L. Shang, Z. Liu, Z. Chen, L. Gu, Z. Tang, T. Zhang, and S. Lu, “ A
general route to prepare low-ruthenium-content bimetallic electrocatalysts for
pH-universal hydrogen evolution reaction by using carbon quantum dots,” Angew.
Chem., Int. Ed. 59(4), 1718–1726 (2020).
https://doi.org/10.1002/anie.20191391050. Y. Pi, Q. Shao, P. Wang, J. Guo, and
X. Huang, “ General formation of monodisperse IrM (M = Ni, Co, Fe) bimetallic
nanoclusters as bifunctional electrocatalysts for acidic overall water
splitting,” Adv. Funct. Mater. 27(27), 1700886 (2017).
https://doi.org/10.1002/adfm.201700886127. Q. Wang, M. Ming, S. Niu, Y. Zhang,
G. Fan, and J. S. Hu, “ Scalable solid-state synthesis of highly dispersed
uncapped metal (Rh, Ru, Ir) nanoparticles for efficient hydrogen evolution,”
Adv. Energy Mater. 8(31), 1801698 (2018).
https://doi.org/10.1002/aenm.201801698128. M. Ming, Y. Zhang, C. He, L. Zhao, S.
Niu, G. Fan, and J. S. Hu, “ Room-temperature sustainable synthesis of selected
platinum group metal (PGM = Ir, Rh, and Ru) nanocatalysts well-dispersed on
porous carbon for efficient hydrogen evolution and oxidation,” Small 15(49),
1903057 (2019). https://doi.org/10.1002/smll.201903057229. Y. Liu, Y. Yang, Z.
Peng, Z. Liu, Z. Chen, L. Shang, S. Lu, and T. Zhang, “ Self-crosslinking carbon
dots loaded ruthenium dots as an efficient and super-stable hydrogen production
electrocatalyst at all pH values,” Nano Energy 65, 104023 (2019).
https://doi.org/10.1016/j.nanoen.2019.104023232. W. Li, Y. Liu, M. Wu, X. Feng,
S. A. Redfern, Y. Shang, X. Yong, T. Feng, K. Wu, and Z. Liu, “
Carbon-quantum-dots-loaded ruthenium nanoparticles as an efficient
electrocatalyst for hydrogen production in alkaline media,” Adv. Mater. 30(31),
1800676 (2018). https://doi.org/10.1002/adma.201800676 Hu's group developed a
facile solid-state approach [Fig. 22(a)], in which the mixed precursors [NaOH,
NaBH4, MCl3 (M = Rh, Ru, and Ir), and carbon supports] were directly grinded in
an agate mortar at room temperature, to anchor a series of noble metal
nanoparticles (Rh, Ru, and Ir) on various carbon supports, such as XC-72 Vulcan
carbon, Ketjenblack, Super P, etc., and eventually form the M NP/C (M = Rh, Ru,
Ir) nanohybrids.127127. Q. Wang, M. Ming, S. Niu, Y. Zhang, G. Fan, and J. S.
Hu, “ Scalable solid-state synthesis of highly dispersed uncapped metal (Rh, Ru,
Ir) nanoparticles for efficient hydrogen evolution,” Adv. Energy Mater. 8(31),
1801698 (2018). https://doi.org/10.1002/aenm.201801698 All resulting samples
featured these noble metal NPs with an ultrasmall size, a good uniformity, and a
high dispersion on the carbon matrixes [Fig. 22(b)]. The authors pointed out
that such morphological properties were free from the types and surface areas of
carbon, but was largely related to the standard reduction potentials of
different metals. The lowest redox potential for Ru/Ru3+ corresponded to the
smallest size, followed by Rh metal, and then Ir metal with the largest size
[Figs. 22(c)–22(e)]. What's more, in absence of carbon supports, irregular and
interconnected large particles were observed. By virtue of the high intrinsic
activity of noble metals and above features, all as-prepared materials, i.e., Rh
NP/C, Ir NP/C, and Ru NP/C, showed impressive HER activities and durability in 1
M KOH, among which, Rh NP/C was the most excellent one with only a 7 mV
overpotential at 10 mA cm−2 [Fig. 22(f)], ranking among the top series of these
noble metal electrocatalysts used for alkaline HER. Soon afterwards, the same
group reported an analogous crafting of ultrafine-sized platinum-group metals
(Ir, Rh, and Ru) well-dispersed on the as-formed porous carbon (PC) via
efficient electroless deposition. This deposition process was triggered by
surface oxygen-based-functional group-functionalized PC with strong
reducibility.128128. M. Ming, Y. Zhang, C. He, L. Zhao, S. Niu, G. Fan, and J.
S. Hu, “ Room-temperature sustainable synthesis of selected platinum group metal
(PGM = Ir, Rh, and Ru) nanocatalysts well-dispersed on porous carbon for
efficient hydrogen evolution and oxidation,” Small 15(49), 1903057 (2019).
https://doi.org/10.1002/smll.201903057 As expected, these obtained nanohybrids
also granted a remarkable catalytic performance toward hydrogen production in
both alkaline and acid media. Freestanding zero-valent Pd (Pd0)/graphdiyne (GDY)
composites on carbon cloth was also constructed by solvothermal treatment of
carbon cloth (CC) with pyridine and following electrochemical deposition in
PdCl2 solution, which contained the vertical arrays of interlaced GDY nanosheets
on the surface of the smooth interweaved carbon fibers and the firmly attached
Pd0 atoms on GDY with a very low loading of about 0.2 wt. %.223223. H. Yu, Y.
Xue, B. Huang, L. Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “
Ultrathin nanosheet of graphdiyne-supported palladium atom catalyst for
efficient hydrogen production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006 Such chemical composition and unique
micro-structures enabled the Pd0/GDY sample to be an unusual cathodic
electrocatalyst for HER with needing the overpotential of 55 mV to reach 10 mA
cm−2, a high mass activity of 61.5 A mg−1metal, and a long-term durability for
at least 72 h. Combining appropriate amount of Ru dots with self-crosslinking
CQDs (Ru@SC-CQDs) [Figs. 22(g) and 22(h)], Zhang's group demonstrated the decent
catalytic ability for HER at all pH levels. The overpotentials of Ru@SC-CQDs
were 29, 59, and 66 mV in 1 M KOH, 0.5 M H2SO4, and 1 M PBS,
respectively.229229. Y. Liu, Y. Yang, Z. Peng, Z. Liu, Z. Chen, L. Shang, S. Lu,
and T. Zhang, “ Self-crosslinking carbon dots loaded ruthenium dots as an
efficient and super-stable hydrogen production electrocatalyst at all pH
values,” Nano Energy 65, 104023 (2019).
https://doi.org/10.1016/j.nanoen.2019.104023 Guided by experimental evidences
and DFT calculations, a synergistic positive attribute of Ru dots and SC-CQDs
should be answerable for the remarkable HER catalytic behavior [Fig. 22(i)].
Likewise, the admirable catalytic materials by introducing CQDs supports into
RuM (M = Ni, Mn, and Cu) alloys over the whole pH range were also put forward by
Zhang's group.4949. Y. Liu, X. Li, Q. Zhang, W. Li, Y. Xie, H. Liu, L. Shang, Z.
Liu, Z. Chen, L. Gu, Z. Tang, T. Zhang, and S. Lu, “ A general route to prepare
low-ruthenium-content bimetallic electrocatalysts for pH-universal hydrogen
evolution reaction by using carbon quantum dots,” Angew. Chem., Int. Ed. 59(4),
1718–1726 (2020). https://doi.org/10.1002/anie.201913910
FIG. 22. (a) A schematic diagram depicting the formation process of the M NP/C
(M = Rh, Ru, and Ir) nanohybrids. (b) A high-magnification TEM image of Rh NP/C.
(c)–(e) The size distribution diagram of different metal nanoparticles, i.e.,
(c) Rh NP, (d) Ru NP, and (e) Ir NP. (f) The HER activity of M NP/C and Pt/C in
alkaline media. Reproduced with permission from Wang et al., Adv. Energy Mater.
8(31), 1801698 (2018). Copyright 2018 Wiley-VCH. (g) TEM and (h) HRTEM images of
the as-prepared Ru@SC-CQDs. (i) The proposed reaction steps for HER on Ru13
anchored on N doped SC-carbon dots (CDs) (water dissociation and hydrogen
formation). Reproduced with permission from Liu et al., Nano Energy 65, 104023
(2019). Copyright 2019 Elsevier.
* PPT
|
* High-resolution
In addition to above these as-formed carbon matrixes, various in situ formed
functional carbon derived from the pyrolysis of organic precursors during the
growth of metal nanoparticles can play a better role in uniformly and tightly
anchoring metal nanoparticles or efficiently restricting their
growth.12,16,55–59,21912. J. Yu, Q. He, G. Yang, W. Zhou, Z. Shao, and M. Ni, “
Recent advances and prospective in ruthenium-based materials for electrochemical
water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b0245716. P. Jiang, H. Huang, J. Diao, S.
Gong, S. Chen, J. Lu, C. Wang, Z. Sun, G. Xia, and K. Yang, “ Improving
electrocatalytic activity of iridium for hydrogen evolution at high current
densities above 1000 mA cm−2,” Appl. Catal. B 258(5), 117965 (2019).
https://doi.org/10.1016/j.apcatb.2019.11796555. P. Jiang, J. Chen, C. Wang, K.
Yang, S. Gong, S. Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the activity
of carbon for electrocatalytic hydrogen evolution via an iridium-cobalt alloy
core encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324
(2018). https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K.
Yang, J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated
graphene shell encapsulating iridium-nickel alloy as an efficient
electrocatalyst towards hydrogen evolution reaction,” J. Mater. Chem. A 7(25),
15079–15088 (2019). https://doi.org/10.1039/C9TA04361F57. J. Chen, G. Xia, P.
Jiang, Y. Yang, R. Li, R. Shi, J. Su, and Q. Chen, “ Active and durable hydrogen
evolution reaction catalyst derived from Pd-doped metal-organic frameworks,” ACS
Appl. Mater. Interfaces 8(21), 13378–13383 (2016).
https://doi.org/10.1021/acsami.6b0126658. J. Su, Y. Yang, G. Xia, J. Chen, P.
Jiang, and Q. Chen, “ Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped
graphene as active electrocatalysts for producing hydrogen in alkaline media,”
Nat. Commun. 8, 14969 (2017). https://doi.org/10.1038/ncomms1496959. Y. Xu, S.
Yin, C. Li, K. Deng, H. Xue, X. Li, H. Wang, and L. Wang, “
Low-ruthenium-content NiRu nanoalloys encapsulated in nitrogen-doped carbon as
highly efficient and pH-universal electrocatalysts for the hydrogen evolution
reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H219. J. Mahmood, M. A. R. Anjum, S. H. Shin,
I. Ahmad, H. J. Noh, S. J. Kim, H. Y. Jeong, J. S. Lee, and J. B. Baek, “
Encapsulating iridium nanoparticles inside a 3D cage-like organic network as an
efficient and durable catalyst for the hydrogen evolution reaction,” Adv. Mater.
30(52), 1805606 (2018). https://doi.org/10.1002/adma.201805606 To this regard,
Zhou and his co-workers designed small Au nanoparticles in a 20 nm size adhered
on N-doped carbon architecture (Au@NC) by first bioreduction of Au3+ with
microorganism (Pycnoporus sanguineus cells) to form this Au/microorganism
composite and then calcining it in an Ar atmosphere for achieving the resulting
Au@NC.217217. W. Zhou, T. Xiong, C. Shi, J. Zhou, K. Zhou, N. Zhu, L. Li, Z.
Tang, and S. Chen, “ Bioreduction of precious metals by microorganism: Efficient
Gold@N-doped carbon electrocatalysts for the hydrogen evolution reaction,”
Angew. Chem., Int. Ed. 55(29), 8416–8420 (2016).
https://doi.org/10.1002/anie.201602627 This Au@NC hybrid exhibited a good
catalytic performance for HER under acidic conditions, with an onset potential
of 54.1 mV and a Tafel slope of 76.8 mV dec−1. Recently, as reported by Baek's
group, the empty d orbitals in Ir sites could be well modulated through a strong
interaction with the p orbitals of C/N atoms, which would further balance
hydrogen adsorption/desorption behaviors around Ir sites, and thereby
accelerated the related HER process [Figs. 23(a) and 23(b)].203203. F. Li, G.-F.
Han, H.-J. Noh, J.-P. Jeon, I. Ahmad, S. Chen, C. Yang, Y. Bu, Z. Fu, and Y. Lu,
“ Balancing hydrogen adsorption/desorption by orbital modulation for efficient
hydrogen evolution catalysis,” Nat. Commun. 10, 4060 (2019).
https://doi.org/10.1038/s41467-019-12012-z Motivated by the theoretical
calculations, Ir nanodots firmly supported on hollow nitrogenated carbon
nanospheres with a low-Ir amount (about 7.16 wt. %) (denoted as IrHNC) were
prepared via the confined pyrolysis of this polystyrene (PS)
microsphere@Ir3+–polydopamine (PDA) composite [Fig. 23(c)]. As expected, the
as-obtained IrHNC delivered an incredible HER activity in acidic electrolytes,
which included the smallest reported a η10 of 4.5 mV, and the largest mass
activity of 1.12 A mgIr−1 at the overpotential of 10 mV, and the TOF value of
4.21 H2 s−1 at the 25 mV overpotential by far, strikingly surpassing pure Ir
nanoparticles and the benchmark Pt/C [Figs. 23(d)–23(f)]. Analogously, in the
same group, a prominent all-round HER catalysis previously has been presented by
the ultrasmall-sized Ru nanoparticles uniformly coated with a two-dimensional
holey nitrogenated carbon structure (Ru@C2N), which was constructed via a
combined polycondensation-reduction-pyrolysis route.233233. J. Mahmood, F. Li,
S.-M. Jung, M. S. Okyay, I. Ahmad, S.-J. Kim, N. Park, H. Y. Jeong, and J.-B.
Baek, “ An efficient and pH-universal ruthenium-based catalyst for the hydrogen
evolution reaction,” Nat. Nanotechnol. 12(5), 441–446 (2017).
https://doi.org/10.1038/nnano.2016.304 Later, importantly, it was discovered
that RuNxCy moieties might stand out as the most active centers for HER in such
a Ru–N–C system, as verified by Bai et al.227227. L. Bai, Z. Duan, X. Wen, R.
Si, Q. Zhang, and J. Guan, “ Highly dispersed ruthenium-based multifunctional
electrocatalyst,” ACS Catal. 9(11), 9897–9904 (2019).
https://doi.org/10.1021/acscatal.9b03514 and Lu et al.234234. B. Lu, L. Guo, F.
Wu, Y. Peng, J. E. Lu, T. J. Smart, N. Wang, Y. Z. Finfrock, D. Morris, and P.
Zhang, “ Ruthenium atomically dispersed in carbon outperforms platinum toward
hydrogen evolution in alkaline media,” Nat. Commun. 10, 631 (2019).
https://doi.org/10.1038/s41467-019-08419-3 Another prominent study involving
this metal-in situ carbon composite was reported by Li and his co-workers, who
integrated Ru/Ni nanoparticles with 1D N-doped carbon nanofibers (RuNi–NCNFs)
through an accessible electrospinning technique with subsequent carbonization
treatment.228228. M. Li, H. Wang, W. Zhu, W. Li, C. Wang, and X. Lu, “ RuNi
nanoparticles embedded in N-doped carbon nanofibers as a robust bifunctional
catalyst for efficient overall water splitting,” Adv. Sci. 7(2), 1901833 (2020).
https://doi.org/10.1002/advs.201901833 The synergistic effect stemming from Ru
and Ni, conductive NCNF supports, and high active surface area granted
RuNi–NCNFs a fascinating HER electrocatalytic activity in both the base and
acid, yielding the small η10 values of 35 and 23 mV, respectively. Besides, a
good OER activity for this material was also achieved in alkaline media. By
utilizing the advantages of MOFs, a raw material with evenly and periodically
distributed atoms and a distinguished self-sacrificial template, all sorts of
functional carbon-metal-related nanostructured composites were
fabricated.55–5955. P. Jiang, J. Chen, C. Wang, K. Yang, S. Gong, S. Liu, Z.
Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the activity of carbon for
electrocatalytic hydrogen evolution via an iridium-cobalt alloy core
encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324 (2018).
https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K. Yang,
J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated graphene
shell encapsulating iridium-nickel alloy as an efficient electrocatalyst towards
hydrogen evolution reaction,” J. Mater. Chem. A 7(25), 15079–15088 (2019).
https://doi.org/10.1039/C9TA04361F57. J. Chen, G. Xia, P. Jiang, Y. Yang, R. Li,
R. Shi, J. Su, and Q. Chen, “ Active and durable hydrogen evolution reaction
catalyst derived from Pd-doped metal-organic frameworks,” ACS Appl. Mater.
Interfaces 8(21), 13378–13383 (2016). https://doi.org/10.1021/acsami.6b0126658.
J. Su, Y. Yang, G. Xia, J. Chen, P. Jiang, and Q. Chen, “ Ruthenium-cobalt
nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts
for producing hydrogen in alkaline media,” Nat. Commun. 8, 14969 (2017).
https://doi.org/10.1038/ncomms1496959. Y. Xu, S. Yin, C. Li, K. Deng, H. Xue, X.
Li, H. Wang, and L. Wang, “ Low-ruthenium-content NiRu nanoalloys encapsulated
in nitrogen-doped carbon as highly efficient and pH-universal electrocatalysts
for the hydrogen evolution reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H Su and his co-workers, for the first time,
synthesized the RuCo nanoalloys with a low concentration embedded in an N-doped
graphene-like carbon layer (RuCo@NC) derived from a Ru cation-impregnated
Co-based MOF, which manifested a splendid HER performance. In this system, such
good catalytic properties were mainly ascribed to that the N-doped carbon shell
with a well modified electronic structure from metal cores helped to favor the
formation of carbon–hydrogen, thereupon optimizing ΔGH* of the HER, as
elaborated in Sec. IV A 1.5858. J. Su, Y. Yang, G. Xia, J. Chen, P. Jiang, and
Q. Chen, “ Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped graphene
as active electrocatalysts for producing hydrogen in alkaline media,” Nat.
Commun. 8, 14969 (2017). https://doi.org/10.1038/ncomms14969 Following this
work, parallel catalytic mechanisms were extensively proposed in several other
alloys@N-doped carbon systems for HER, like CoPd@NC, IrCo@NC, RuNi@NC,
etc.55–57,5955. P. Jiang, J. Chen, C. Wang, K. Yang, S. Gong, S. Liu, Z. Lin, M.
Li, G. Xia, and Y. Yang, “ Tuning the activity of carbon for electrocatalytic
hydrogen evolution via an iridium-cobalt alloy core encapsulated in
nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324 (2018).
https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K. Yang,
J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated graphene
shell encapsulating iridium-nickel alloy as an efficient electrocatalyst towards
hydrogen evolution reaction,” J. Mater. Chem. A 7(25), 15079–15088 (2019).
https://doi.org/10.1039/C9TA04361F57. J. Chen, G. Xia, P. Jiang, Y. Yang, R. Li,
R. Shi, J. Su, and Q. Chen, “ Active and durable hydrogen evolution reaction
catalyst derived from Pd-doped metal-organic frameworks,” ACS Appl. Mater.
Interfaces 8(21), 13378–13383 (2016). https://doi.org/10.1021/acsami.6b0126659.
Y. Xu, S. Yin, C. Li, K. Deng, H. Xue, X. Li, H. Wang, and L. Wang, “
Low-ruthenium-content NiRu nanoalloys encapsulated in nitrogen-doped carbon as
highly efficient and pH-universal electrocatalysts for the hydrogen evolution
reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H In another published work, a Ru-decorated
hierarchical porous carbon nanohybrid (named as Ru–HPC) was prepared via a
bimetallic MOF (CuRu–MOF)-based strategy.235235. T. Qiu, Z. Liang, W. Guo, S.
Gao, C. Qu, H. Tabassum, H. Zhang, B. Zhu, R. Zou, and Y. Shao-Horn, “ Highly
exposed ruthenium-based electrocatalysts from bimetallic metal-organic
frameworks for overall water splitting,” Nano Energy 58, 1–10 (2019).
https://doi.org/10.1016/j.nanoen.2018.12.085 The Ru–HPC showed ultrafine Ru
nanoparticles, high exposure, hierarchical porous carbon structure, high
conductivity and low Ru content, thus resulting in an extraordinary catalytic
activity for HER.
FIG. 23. (a) The electron-density isosurfaces for Ir (top) and IrHNC (down) with
H adsorption. (b) The free energy of H adsorption for the Ir, IrHNC, and Pt. (c)
The TEM image of IrHNC. (d) HER polarization curves of the as-obtained IrHNC, Ir
nanoparticles, and benchmark Pt/C in an acidic solution. (e) The mass activities
of these samples at 10 and 30 mV overpotentials. (f) The TOF comparison of the
as-prepared IrHNC and other reported catalytic materials under acidic
conditions. Reproduced with permission from Li et al., Nat. Commun. 10, 4060
(2019). Copyright 2019 Nature Publishing Group.
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* High-resolution
It is worth mentioning that doping foreign non-metallic elements (such as N, B,
F, P, etc.) into the carbon backbone can further ameliorate the catalytic
properties in HER.53,180,222–224,226–228,23653. L. Zhang, J. Lu, S. Yin, L. Luo,
S. Jing, A. Brouzgou, J. Chen, P. K. Shen, and P. Tsiakaras, “ One-pot
synthesized boron-doped RhFe alloy with enhanced catalytic performance for
hydrogen evolution reaction,” Appl. Catal. B 230(15), 58–64 (2018).
https://doi.org/10.1016/j.apcatb.2018.02.034180. J. Yu, G. Li, H. Liu, L. Zhao,
A. Wang, Z. Liu, H. Li, H. Liu, Y. Hu, and W. Zhou, “ Ru-Ru2P@NPC and NPC@RuO2
synthesized via environment-friendly and solid-phase phosphating process by
saccharomycetes as N/P sources and carbon template for overall water splitting
in acid electrolyte,” Adv. Funct. Mater. 29(22), 1901154 (2019).
https://doi.org/10.1002/adfm.201901154222. S. Zhou, X. Chen, P. Yu, F. Gao, and
L. Mao, “ Nitrogen-doped carbon nanotubes as an excellent substrate for
electroless deposition of Pd nanoparticles with a high efficiency toward the
hydrogen evolution reaction,” Electrochem. Commun. 90, 91–95 (2018).
https://doi.org/10.1016/j.elecom.2018.04.015223. H. Yu, Y. Xue, B. Huang, L.
Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “ Ultrathin
nanosheet of graphdiyne-supported palladium atom catalyst for efficient hydrogen
production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006224. K. Guo, L. J. Rowland, L. H.
Isherwood, G. Glodan, and A. Baidak, “ Photon-induced synthesis of ultrafine
metal nanoparticles on graphene as electrocatalysts: Impact of functionalization
and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B226. W. Shen, L. Ge, Y. Sun, F. Liao, L. Xu,
Q. Dang, Z. Kang, and M. Shao, “ Rhodium nanoparticles/F-doped graphene
composites as multifunctional electrocatalyst superior to Pt/C for hydrogen
evolution and formic acid oxidation reaction,” ACS Appl. Mater. Interfaces
10(39), 33153–33161 (2018). https://doi.org/10.1021/acsami.8b09297227. L. Bai,
Z. Duan, X. Wen, R. Si, Q. Zhang, and J. Guan, “ Highly dispersed
ruthenium-based multifunctional electrocatalyst,” ACS Catal. 9(11), 9897–9904
(2019). https://doi.org/10.1021/acscatal.9b03514228. M. Li, H. Wang, W. Zhu, W.
Li, C. Wang, and X. Lu, “ RuNi nanoparticles embedded in N-doped carbon
nanofibers as a robust bifunctional catalyst for efficient overall water
splitting,” Adv. Sci. 7(2), 1901833 (2020).
https://doi.org/10.1002/advs.201901833236. S. Ye, F. Luo, T. Xu, P. Zhang, H.
Shi, S. Qin, J. Wu, C. He, X. Ouyang, and Q. Zhang, “ Boosting the alkaline
hydrogen evolution of Ru nanoclusters anchored on B/N-doped graphene by
accelerating water dissociation,” Nano Energy 68, 104301 (2020).
https://doi.org/10.1016/j.nanoen.2019.104301 In particular, the N dopant is
widely welcomed, as exemplified by numerous previous works, like above
mentioned.55–59,222–224,226–22855. P. Jiang, J. Chen, C. Wang, K. Yang, S. Gong,
S. Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the activity of carbon for
electrocatalytic hydrogen evolution via an iridium-cobalt alloy core
encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324 (2018).
https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K. Yang,
J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated graphene
shell encapsulating iridium-nickel alloy as an efficient electrocatalyst towards
hydrogen evolution reaction,” J. Mater. Chem. A 7(25), 15079–15088 (2019).
https://doi.org/10.1039/C9TA04361F57. J. Chen, G. Xia, P. Jiang, Y. Yang, R. Li,
R. Shi, J. Su, and Q. Chen, “ Active and durable hydrogen evolution reaction
catalyst derived from Pd-doped metal-organic frameworks,” ACS Appl. Mater.
Interfaces 8(21), 13378–13383 (2016). https://doi.org/10.1021/acsami.6b0126658.
J. Su, Y. Yang, G. Xia, J. Chen, P. Jiang, and Q. Chen, “ Ruthenium-cobalt
nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts
for producing hydrogen in alkaline media,” Nat. Commun. 8, 14969 (2017).
https://doi.org/10.1038/ncomms1496959. Y. Xu, S. Yin, C. Li, K. Deng, H. Xue, X.
Li, H. Wang, and L. Wang, “ Low-ruthenium-content NiRu nanoalloys encapsulated
in nitrogen-doped carbon as highly efficient and pH-universal electrocatalysts
for the hydrogen evolution reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H222. S. Zhou, X. Chen, P. Yu, F. Gao, and L.
Mao, “ Nitrogen-doped carbon nanotubes as an excellent substrate for electroless
deposition of Pd nanoparticles with a high efficiency toward the hydrogen
evolution reaction,” Electrochem. Commun. 90, 91–95 (2018).
https://doi.org/10.1016/j.elecom.2018.04.015223. H. Yu, Y. Xue, B. Huang, L.
Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “ Ultrathin
nanosheet of graphdiyne-supported palladium atom catalyst for efficient hydrogen
production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006224. K. Guo, L. J. Rowland, L. H.
Isherwood, G. Glodan, and A. Baidak, “ Photon-induced synthesis of ultrafine
metal nanoparticles on graphene as electrocatalysts: Impact of functionalization
and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B226. W. Shen, L. Ge, Y. Sun, F. Liao, L. Xu,
Q. Dang, Z. Kang, and M. Shao, “ Rhodium nanoparticles/F-doped graphene
composites as multifunctional electrocatalyst superior to Pt/C for hydrogen
evolution and formic acid oxidation reaction,” ACS Appl. Mater. Interfaces
10(39), 33153–33161 (2018). https://doi.org/10.1021/acsami.8b09297227. L. Bai,
Z. Duan, X. Wen, R. Si, Q. Zhang, and J. Guan, “ Highly dispersed
ruthenium-based multifunctional electrocatalyst,” ACS Catal. 9(11), 9897–9904
(2019). https://doi.org/10.1021/acscatal.9b03514228. M. Li, H. Wang, W. Zhu, W.
Li, C. Wang, and X. Lu, “ RuNi nanoparticles embedded in N-doped carbon
nanofibers as a robust bifunctional catalyst for efficient overall water
splitting,” Adv. Sci. 7(2), 1901833 (2020).
https://doi.org/10.1002/advs.201901833 Heteroatom dopants can give rise to the
asymmetric charge distribution of the adjacent C atoms via breaking their
electroneutrality, which accordingly enhances the bonding filling between the
bonding orbital of H* and the hybridized orbital of active C, eventually to
diminish |ΔGH*| for an improved HER activity.5555. P. Jiang, J. Chen, C. Wang,
K. Yang, S. Gong, S. Liu, Z. Lin, M. Li, G. Xia, and Y. Yang, “ Tuning the
activity of carbon for electrocatalytic hydrogen evolution via an iridium-cobalt
alloy core encapsulated in nitrogen-doped carbon cages,” Adv. Mater. 30(9),
1705324 (2018). https://doi.org/10.1002/adma.201705324 For the above-discussed
alloys@N-doped carbon systems, N atoms substantially served as a link for
electron transfer from the alloy core to active C atoms neighboring on N
dopants.55–5955. P. Jiang, J. Chen, C. Wang, K. Yang, S. Gong, S. Liu, Z. Lin,
M. Li, G. Xia, and Y. Yang, “ Tuning the activity of carbon for electrocatalytic
hydrogen evolution via an iridium-cobalt alloy core encapsulated in
nitrogen-doped carbon cages,” Adv. Mater. 30(9), 1705324 (2018).
https://doi.org/10.1002/adma.20170532456. S. Gong, C. Wang, P. Jiang, K. Yang,
J. Lu, M. Huang, S. Chen, J. Wang, and Q. Chen, “ O species-decorated graphene
shell encapsulating iridium-nickel alloy as an efficient electrocatalyst towards
hydrogen evolution reaction,” J. Mater. Chem. A 7(25), 15079–15088 (2019).
https://doi.org/10.1039/C9TA04361F57. J. Chen, G. Xia, P. Jiang, Y. Yang, R. Li,
R. Shi, J. Su, and Q. Chen, “ Active and durable hydrogen evolution reaction
catalyst derived from Pd-doped metal-organic frameworks,” ACS Appl. Mater.
Interfaces 8(21), 13378–13383 (2016). https://doi.org/10.1021/acsami.6b0126658.
J. Su, Y. Yang, G. Xia, J. Chen, P. Jiang, and Q. Chen, “ Ruthenium-cobalt
nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts
for producing hydrogen in alkaline media,” Nat. Commun. 8, 14969 (2017).
https://doi.org/10.1038/ncomms1496959. Y. Xu, S. Yin, C. Li, K. Deng, H. Xue, X.
Li, H. Wang, and L. Wang, “ Low-ruthenium-content NiRu nanoalloys encapsulated
in nitrogen-doped carbon as highly efficient and pH-universal electrocatalysts
for the hydrogen evolution reaction,” J. Mater. Chem. A 6(4), 1376–1381 (2018).
https://doi.org/10.1039/C7TA09939H The electrons first transferred from the
metal core to the N atoms of the carbon layer, and then these N atoms further
tailored the electronic arrangements of adjacent C atoms, rendering these C
atoms as electrocatalytically efficient active sites for the favorable formation
of C–H. In a recent study, the authors analyzed the effects of graphene
functionalization and doping by synthesizing four graphene materials, i.e., GO,
rGO, electrochemically exfoliated graphene (G), N-doped graphene (NG) as
supports to load small Pd nanoparticles.224224. K. Guo, L. J. Rowland, L. H.
Isherwood, G. Glodan, and A. Baidak, “ Photon-induced synthesis of ultrafine
metal nanoparticles on graphene as electrocatalysts: Impact of functionalization
and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B It was found that among them, NG as a
skeleton can produce the Pd nanoparticles in an ultrafine size (∼3 nm) and with
high dispersion, and this Pd/NG composite presented the lowest HER overpotential
in acid. N dopants, especially the graphitic N, were disclosed to play a
critical role in immobilizing and stabilizing these as-formed Pd nanoparticles
by the electronic interaction between Pd and N. Besides, B-doped functional
carbon or F-doped graphene was also utilized as a skeleton for the growth of
RhFe alloy or Rh nanoparticles, respectively.53,22653. L. Zhang, J. Lu, S. Yin,
L. Luo, S. Jing, A. Brouzgou, J. Chen, P. K. Shen, and P. Tsiakaras, “ One-pot
synthesized boron-doped RhFe alloy with enhanced catalytic performance for
hydrogen evolution reaction,” Appl. Catal. B 230(15), 58–64 (2018).
https://doi.org/10.1016/j.apcatb.2018.02.034226. W. Shen, L. Ge, Y. Sun, F.
Liao, L. Xu, Q. Dang, Z. Kang, and M. Shao, “ Rhodium nanoparticles/F-doped
graphene composites as multifunctional electrocatalyst superior to Pt/C for
hydrogen evolution and formic acid oxidation reaction,” ACS Appl. Mater.
Interfaces 10(39), 33153–33161 (2018). https://doi.org/10.1021/acsami.8b09297
Both B and F atoms could adjust the electronic structure of carbon scaffold to
obtain a proper hydrogen-adsorption ability, which brought the striking
enhancement in the HER activity. Most recently, through pyrolyzing the mixed
precursors of H3BO3, Ru(phen)2Cl2, and graphene, Ru nanoclusters combined with
B, N-codoped graphene (Ru NCs/BNG) were created.236236. S. Ye, F. Luo, T. Xu, P.
Zhang, H. Shi, S. Qin, J. Wu, C. He, X. Ouyang, and Q. Zhang, “ Boosting the
alkaline hydrogen evolution of Ru nanoclusters anchored on B/N-doped graphene by
accelerating water dissociation,” Nano Energy 68, 104301 (2020).
https://doi.org/10.1016/j.nanoen.2019.104301 Remarkably, when B was introduced
into graphene structure, the agglomeration of metal particles was inhibited and
induced the formation of Ru NCs nanodots with an ultra-small size (0.5–1 nm)
[Figs. 24(a) and 24(b)]. Moreover, the vacant 2p orbitals in the B atom could be
delocalized to Ru nanodots, which promoted the coordination effect of the
electron-deficient Ru with the lone-pair electrons of O atoms from water
molecules, thereby driving the cleavage of this H–OH bond and expediting the
alkaline hydrogen-evolution dynamics [Figs. 24(d) and 24(e)]. As a consequence,
a brilliant HER catalytic performance was realized in the Ru NCs/BNG catalyst,
featured by a small overpotential of 14 mV at 10 mA cm−2 and stable long-time
operation, which was better than that of 20% Pt [Fig. 24(c)].
FIG. 24. (a) TEM and (b) HRTEM images of Ru NCs/BNG. (c) The HER activity of
different catalytic materials in 1 M KOH. (d) The used calculation structure
model and electronic density distribution. (e) Free energy of the HER pathway
for different catalytic electrodes. Reproduced with permission from Ye et al.,
Nano Energy 68, 104301 (2020). Copyright 2020 Elsevier.
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* High-resolution
Semiconducting carbon nitrides (C3N4) are also selected as the supporting
architecture to anchor noble metal nanoparticles, and become a new class of
composite catalysts.230,231,237–239230. T. Bhowmik, M. K. Kundu, and S. Barman,
“ Palladium nanoparticle-graphitic carbon nitride porous synergistic catalyst
for hydrogen evolution/oxidation reactions over a broad range of pH and
correlation of its catalytic activity with measured hydrogen binding energy,”
ACS Catal. 6(3), 1929–1941 (2016). https://doi.org/10.1021/acscatal.5b02485231.
T. Bhowmik, M. K. Kundu, and S. Barman, “ Growth of one-dimensional RuO2
nanowires on g-carbon nitride: An active and stable bifunctional electrocatalyst
for hydrogen and oxygen evolution reactions at all pH values,” ACS Appl. Mater.
Interfaces 8(42), 28678–28688 (2016). https://doi.org/10.1021/acsami.6b10436237.
M. K. Kundu, T. Bhowmik, and S. Barman, “ Gold aerogel supported on graphitic
carbon nitride: An efficient electrocatalyst for oxygen reduction reaction and
hydrogen evolution reaction,” J. Mater. Chem. A 3(46), 23120–23135 (2015).
https://doi.org/10.1039/C5TA06740E238. Y. Peng, B. Lu, L. Chen, N. Wang, J. E.
Lu, Y. Ping, and S. Chen, “ Hydrogen evolution reaction catalyzed by ruthenium
ion-complexed graphitic carbon nitride nanosheets,” J. Mater. Chem. A 5(34),
18261–18269 (2017). https://doi.org/10.1039/C7TA03826G239. R. Nazir, P. Fageria,
M. Basu, and S. Pande, “ Decoration of carbon nitride surface with bimetallic
nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via galvanic exchange for hydrogen
evolution reaction,” J. Phys. Chem. C 121(36), 19548–19558 (2017).
https://doi.org/10.1021/acs.jpcc.7b04595 C3N4, as a supporting material for
electrocatalysis, possesses multifold merits. With the existence of N
heteroatoms and repetitive tri-s-triazine units in the C3N4 framework, metal
nanoparticles can be readily coordinated and stabilized, which rendered the
promoted electrical connection and electron transfer.239239. R. Nazir, P.
Fageria, M. Basu, and S. Pande, “ Decoration of carbon nitride surface with
bimetallic nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via galvanic exchange for
hydrogen evolution reaction,” J. Phys. Chem. C 121(36), 19548–19558 (2017).
https://doi.org/10.1021/acs.jpcc.7b04595 Barman's group communicated the
synthesis of porous Au aerogel decorated on graphitic carbon nitride
(Au-aerogel–CNx) by adopting sodium borohydride as the reducing agent and
undergoing ultrasonication.237237. M. K. Kundu, T. Bhowmik, and S. Barman, “
Gold aerogel supported on graphitic carbon nitride: An efficient electrocatalyst
for oxygen reduction reaction and hydrogen evolution reaction,” J. Mater. Chem.
A 3(46), 23120–23135 (2015). https://doi.org/10.1039/C5TA06740E On account of a
unique synergistic interaction between the two components of porous Au aerogel
and CNx, such Au-aerogel–CNx recorded a superior HER electrocatalytic activity
with an onset overpotential of 30 mV and a Tafel slope of 53 mV dec−1 in 0.5 M
H2SO4. In like manner, Pd nanoparticles hybridized on graphitic carbon nitrides
(Pd–CNx) with porous morphology have been proved as an efficient and stable
pH-universal electrocatalyst for HER.230230. T. Bhowmik, M. K. Kundu, and S.
Barman, “ Palladium nanoparticle-graphitic carbon nitride porous synergistic
catalyst for hydrogen evolution/oxidation reactions over a broad range of pH and
correlation of its catalytic activity with measured hydrogen binding energy,”
ACS Catal. 6(3), 1929–1941 (2016). https://doi.org/10.1021/acscatal.5b02485 The
porous structure in this Pd–CNx catalyst ensured rapid mass transportation to
the active centers and expedited the easy release of evolved gas. For another,
the intimate coupling of Pd nanoparticles and CNx scaffold offered sufficient
mechanical adhesion and strong electronic contact as well as brought about a
fast electron flow during the cathodic polarization. Also, integration of Ru
with graphitic carbon nitrides (C3N4–Ru) was verified as an outstanding acidic
HER electrocatalyst.238238. Y. Peng, B. Lu, L. Chen, N. Wang, J. E. Lu, Y. Ping,
and S. Chen, “ Hydrogen evolution reaction catalyzed by ruthenium ion-complexed
graphitic carbon nitride nanosheets,” J. Mater. Chem. A 5(34), 18261–18269
(2017). https://doi.org/10.1039/C7TA03826G The high activity of C3N4–Ru was most
likely originated from the generation of Ru–N moieties, where a synergy of Ru
metal centers and the C3N4 supports accelerated the adsorption of hydrogen
during the HER process.
b. Si nanowires
In the past few years, researchers found that Si nanowires (Si NWs) as
supporting carriers could effectively suppress the coarsening and aggregation of
metal particles grown on their surfaces, improve the utilization of these
nanoparticles, and increase the active centres.211–214,240–242211. B. Jiang, Y.
Sun, F. Liao, W. Shen, H. Lin, H. Wang, and M. Shao, “ Rh-Ag-Si ternary
composites: Highly active hydrogen evolution electrocatalysts over Pt-Ag-Si,” J.
Mater. Chem. A 5(4), 1623–1628 (2017). https://doi.org/10.1039/C6TA09619K212. L.
Zhu, H. Lin, Y. Li, F. Liao, Y. Lifshitz, M. Sheng, S.-T. Lee, and M. Shao, “ A
rhodium/silicon co-electrocatalyst design concept to surpass platinum hydrogen
evolution activity at high overpotentials,” Nat. Commun. 7, 12272 (2016).
https://doi.org/10.1038/ncomms12272213. B. Jiang, L. Yang, F. Liao, M. Sheng, H.
Zhao, H. Lin, and M. Shao, “ A stepwise-designed Rh-Au-Si nanocomposite that
surpasses Pt/C hydrogen evolution activity at high overpotentials,” Nano Res.
10(5), 1749–1755 (2017). https://doi.org/10.1007/s12274-017-1447-0214. M. Sheng,
B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y. Lifshitz, S.-T. Lee, and M.
Shao, “ Approaching the volcano top: Iridium/silicon nanocomposites as efficient
electrocatalysts for the hydrogen evolution reaction,” ACS Nano 13(3), 2786–2794
(2019). https://doi.org/10.1021/acsnano.8b07572240. L. Zhu, Q. Cai, F. Liao, M.
Sheng, B. Wu, and M. Shao, “ Ru-modified silicon nanowires as electrocatalysts
for hydrogen evolution reaction,” Electrochem. Commun. 52, 29–33 (2015).
https://doi.org/10.1016/j.elecom.2015.01.012241. F. Liao, B. Jiang, W. Shen, Y.
Chen, Y. Li, Y. Shen, K. Yin, and M. Shao, “ Ir-Au bimetallic nanoparticle
modified silicon nanowires with ultralow content of Ir for hydrogen evolution
reaction,” ChemCatChem 11(8), 2126–2130 (2019).
https://doi.org/10.1002/cctc.201900241242. K. Yin, Y. Cheng, B. Jiang, F. Liao,
and M. Shao, “ Palladium-silicon nanocomposites as a stable electrocatalyst for
hydrogen evolution reaction,” J. Colloid Interface Sci. 522(15), 242–248 (2018).
https://doi.org/10.1016/j.jcis.2018.03.045 Additionally, albeit Si belongs to a
semiconductor, the special surface defect in Si NWs endows them sufficient
electric characteristics. More significantly, in the previously present
theoretical and experimental results, Si NWs showed a low hydrogen desorption
energy and thus hydrogen release on the hydrogen-terminated Si NWs was a rapid
process, consequently offered an improvement of the HER electrocatalytic
activity in the Si NWs-supported precious metals.211–214,240–242211. B. Jiang,
Y. Sun, F. Liao, W. Shen, H. Lin, H. Wang, and M. Shao, “ Rh-Ag-Si ternary
composites: Highly active hydrogen evolution electrocatalysts over Pt-Ag-Si,” J.
Mater. Chem. A 5(4), 1623–1628 (2017). https://doi.org/10.1039/C6TA09619K212. L.
Zhu, H. Lin, Y. Li, F. Liao, Y. Lifshitz, M. Sheng, S.-T. Lee, and M. Shao, “ A
rhodium/silicon co-electrocatalyst design concept to surpass platinum hydrogen
evolution activity at high overpotentials,” Nat. Commun. 7, 12272 (2016).
https://doi.org/10.1038/ncomms12272213. B. Jiang, L. Yang, F. Liao, M. Sheng, H.
Zhao, H. Lin, and M. Shao, “ A stepwise-designed Rh-Au-Si nanocomposite that
surpasses Pt/C hydrogen evolution activity at high overpotentials,” Nano Res.
10(5), 1749–1755 (2017). https://doi.org/10.1007/s12274-017-1447-0214. M. Sheng,
B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y. Lifshitz, S.-T. Lee, and M.
Shao, “ Approaching the volcano top: Iridium/silicon nanocomposites as efficient
electrocatalysts for the hydrogen evolution reaction,” ACS Nano 13(3), 2786–2794
(2019). https://doi.org/10.1021/acsnano.8b07572240. L. Zhu, Q. Cai, F. Liao, M.
Sheng, B. Wu, and M. Shao, “ Ru-modified silicon nanowires as electrocatalysts
for hydrogen evolution reaction,” Electrochem. Commun. 52, 29–33 (2015).
https://doi.org/10.1016/j.elecom.2015.01.012241. F. Liao, B. Jiang, W. Shen, Y.
Chen, Y. Li, Y. Shen, K. Yin, and M. Shao, “ Ir-Au bimetallic nanoparticle
modified silicon nanowires with ultralow content of Ir for hydrogen evolution
reaction,” ChemCatChem 11(8), 2126–2130 (2019).
https://doi.org/10.1002/cctc.201900241242. K. Yin, Y. Cheng, B. Jiang, F. Liao,
and M. Shao, “ Palladium-silicon nanocomposites as a stable electrocatalyst for
hydrogen evolution reaction,” J. Colloid Interface Sci. 522(15), 242–248 (2018).
https://doi.org/10.1016/j.jcis.2018.03.045 All above characteristics suggested
that Si NWs were the promising support materials for electrocatalysis. So far,
Shao's team gave the greatest focus on the research of this noble metal-Si NMs
composite. Numerous composites, e.g., Rh/Si NWs, Rh–Ag–Si NWs, Pd/Si NWs, Ir/Si
NWs, etc., have been built up as efficient HER electrocatalysts.211–214,242211.
B. Jiang, Y. Sun, F. Liao, W. Shen, H. Lin, H. Wang, and M. Shao, “ Rh-Ag-Si
ternary composites: Highly active hydrogen evolution electrocatalysts over
Pt-Ag-Si,” J. Mater. Chem. A 5(4), 1623–1628 (2017).
https://doi.org/10.1039/C6TA09619K212. L. Zhu, H. Lin, Y. Li, F. Liao, Y.
Lifshitz, M. Sheng, S.-T. Lee, and M. Shao, “ A rhodium/silicon
co-electrocatalyst design concept to surpass platinum hydrogen evolution
activity at high overpotentials,” Nat. Commun. 7, 12272 (2016).
https://doi.org/10.1038/ncomms12272213. B. Jiang, L. Yang, F. Liao, M. Sheng, H.
Zhao, H. Lin, and M. Shao, “ A stepwise-designed Rh-Au-Si nanocomposite that
surpasses Pt/C hydrogen evolution activity at high overpotentials,” Nano Res.
10(5), 1749–1755 (2017). https://doi.org/10.1007/s12274-017-1447-0214. M. Sheng,
B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y. Lifshitz, S.-T. Lee, and M.
Shao, “ Approaching the volcano top: Iridium/silicon nanocomposites as efficient
electrocatalysts for the hydrogen evolution reaction,” ACS Nano 13(3), 2786–2794
(2019). https://doi.org/10.1021/acsnano.8b07572242. K. Yin, Y. Cheng, B. Jiang,
F. Liao, and M. Shao, “ Palladium-silicon nanocomposites as a stable
electrocatalyst for hydrogen evolution reaction,” J. Colloid Interface Sci.
522(15), 242–248 (2018). https://doi.org/10.1016/j.jcis.2018.03.045 In 2016,
through a in situ reduction pathway, a Rh/Si NWs composite was designed.
Hydrogen adsorption tended to occur on the Rh site with a large adsorption
energy while Si with a low adsorption energy was used to promote hydrogen
evolution, thus ensuring a satisfactory HER activity in acidic media.212212. L.
Zhu, H. Lin, Y. Li, F. Liao, Y. Lifshitz, M. Sheng, S.-T. Lee, and M. Shao, “ A
rhodium/silicon co-electrocatalyst design concept to surpass platinum hydrogen
evolution activity at high overpotentials,” Nat. Commun. 7, 12272 (2016).
https://doi.org/10.1038/ncomms12272 Meanwhile, Rh-adsorbed hydrogen could
regenerate the Si poisoned by the hydroxyl, which stabilized the catalytic
activity of the Rh/Si NWs material for a long time. Thereafter, this ternary
Rh–Ag–Si system was also investigated as a highly active acidic catalyst for HER
over this Pt–Ag–Si composite.211211. B. Jiang, Y. Sun, F. Liao, W. Shen, H. Lin,
H. Wang, and M. Shao, “ Rh-Ag-Si ternary composites: Highly active hydrogen
evolution electrocatalysts over Pt-Ag-Si,” J. Mater. Chem. A 5(4), 1623–1628
(2017). https://doi.org/10.1039/C6TA09619K Specifically, the optimal Rh–Ag–Si
yielded a η10 of 120 mV, a Tafel slope of 51 mV dec−1, and a mass activity of
11.5 mA mgRh−1 in 0.5 M H2SO4, which were largely superior to those of Pt–Ag–Si
(a η10 of 190 mV, a Tafel slope of 54 mV dec−1, and a mass activity of 2.3 mA
mgPt−1). The DFT results illuminated the activity difference origins, i.e., the
atomic H migration-activation energies from Rh (111) to Si are smaller than the
results from Pt (111) to Si through the Ag surface. Recently, they further tried
to manipulate the Ir metal to achieve an incredible Pt-outperformed activity by
hybridizing with Si NWs to form this Ir/Si NWs hybrid electrocatalyst.214214. M.
Sheng, B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y. Lifshitz, S.-T. Lee,
and M. Shao, “ Approaching the volcano top: Iridium/silicon nanocomposites as
efficient electrocatalysts for the hydrogen evolution reaction,” ACS Nano 13(3),
2786–2794 (2019). https://doi.org/10.1021/acsnano.8b07572 Notably, according to
the Sabatier principle, Ir has a more near-zero/ΔGH/ value (0.03 eV) compared to
Pt (−0.09 eV), and thus theoretically it should possess better HER activity.
Nevertheless, due to a larger enthalpy of atomization for Ir, it shows a
stronger tendency to poor dispersion and severe aggregation. Here, as the
authors showed, the coupling of Ir with Si NWs downsized the metal nanoparticles
to ∼2.2 nm and drove the H2-production process by the three pathways, i.e., H
adsorption on Ir, H diffusion to Si, and H2 desorption from Si. All these
results permitted to attain the promotion on both activity and stability and
exceed the commercial Pt/C in every aspect.
c. Metallic electrodes
Additionally, in some research teams, noble metals spontaneously deposited on
diversified metallic electrodes [e.g., porous Ni, Au (111) or Au (100), Pt
(poly), and Pd (poly) electrodes] also have been utilized for the study of
HER.215,216,243–253215. V. Pérez-Herranz, R. Medina, P. Taymans, C.
González-Buch, E. Ortega, G. Sánchez-Loredo, and G. J. Labrada-Delgado, “
Modification of porous nickel electrodes with silver nanoparticles for hydrogen
production,” J. Electroanal. Chem. 808(1), 420–426 (2018).
https://doi.org/10.1016/j.jelechem.2017.06.022216. Y. Liang, C. Csoklich, D.
McLaughlin, O. Schneider, and A. S. Bandarenka, “ Revealing active sites for
hydrogen evolution at Pt and Pd atomic layers on Au surfaces,” ACS Appl. Mater.
Interfaces 11(13), 12476–12480 (2019).
https://doi.org/10.1021/acsami.8b22146243. S. Pandelov and U. Stimming, “
Reactivity of monolayers and nano-islands of palladium on Au (1 1 1) with
respect to proton reduction,” Electrochim. Acta 52(18), 5548–5555 (2007).
https://doi.org/10.1016/j.electacta.2007.02.043244. P. J. Schäfer and L. A.
Kibler, “ Incorporation of Pd into Au (111): Enhanced electrocatalytic activity
for the hydrogen evolution reaction,” Phys. Chem. Chem. Phys. 12(46),
15225–15230 (2010). https://doi.org/10.1039/c0cp00780c245. M. Smiljanić, I.
Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, “ Catalysis of hydrogen evolution
on Au (111) modified by spontaneously deposited Pd nanoislands,”
Electrocatalysis 3, 369–375 (2012).
https://doi.org/10.1007/s12678-012-0093-2246. S. Strbac, I. Srejic, and Z.
Rakocevic, “ Electrocatalysis of hydrogen evolution reaction on Au (111) by
spontaneously deposited iridium in acid solution,” J. Electrochem. Soc. 165(15),
J3335–J3341 (2018). https://doi.org/10.1149/2.0441815jes247. P. Quaino, E.
Santos, H. Wolfschmidt, M. Montero, and U. Stimming, “ Theory meets experiment:
Electrocatalysis of hydrogen oxidation/evolution at Pd-Au nanostructures,”
Catal. Today 177(1), 55–63 (2011).
https://doi.org/10.1016/j.cattod.2011.05.004248. P. Quaino and E. Santos, “
Hydrogen evolution reaction on palladium multilayers deposited on Au (111): A
theoretical approach,” Langmuir 31(2), 858–867 (2015).
https://doi.org/10.1021/la503881y249. G. Soldano, E. N. Schulz, D. R. Salinas,
E. Santos, and W. Schmickler, “ Hydrogen electrocatalysis on overlayers of
rhodium over gold and palladium substrates-more active than platinum?,” Phys.
Chem. Chem. Phys. 13(36), 16437–16443 (2011).
https://doi.org/10.1039/c1cp21565e250. M. Smiljanić, I. Srejić, B. Grgur, Z.
Rakočević, and S. Štrbac, “ Hydrogen evolution on Au (111) catalyzed by rhodium
nanoislands,” Electrochem. Commun. 28, 37–39 (2013).
https://doi.org/10.1016/j.elecom.2012.12.009251. S. Štrbac, M. Smiljanić, and Z.
Rakočević, “ Spontaneously deposited Rh on Au (111) observed by AFM and XPS:
Electrocatalysis of hydrogen evolution,” J. Electrochem. Soc. 163(12), D3027
(2016). https://doi.org/10.1149/2.0041612jes252. M. Smiljanic, Z. Rakocevic, A.
Maksic, and S. Strbac, “ Hydrogen evolution reaction on platinum catalyzed by
palladium and rhodium nanoislands,” Electrochim. Acta 117(20), 336–343 (2014).
https://doi.org/10.1016/j.electacta.2013.11.142253. S. Štrbac, M. Smiljanić, T.
Wakelin, J. Potočnik, and Z. Rakočević, “ Hydrogen evolution reaction on
bimetallic Ir/Pt (poly) electrodes in alkaline solution,” Electrochim. Acta
306(20), 18–27 (2019). https://doi.org/10.1016/j.electacta.2019.03.100 Amon
them, the single-crystal Au substrate modified with noble metals is a
representative example. For the Pd-deposited single-crystal Au electrode, by
employing different deposition ways and adjusting diverse Pd coverage, the
electronic interplay between Pd overlayer and Au substrate could be modulated to
obtain higher HER activity.243–246243. S. Pandelov and U. Stimming, “ Reactivity
of monolayers and nano-islands of palladium on Au (1 1 1) with respect to proton
reduction,” Electrochim. Acta 52(18), 5548–5555 (2007).
https://doi.org/10.1016/j.electacta.2007.02.043244. P. J. Schäfer and L. A.
Kibler, “ Incorporation of Pd into Au (111): Enhanced electrocatalytic activity
for the hydrogen evolution reaction,” Phys. Chem. Chem. Phys. 12(46),
15225–15230 (2010). https://doi.org/10.1039/c0cp00780c245. M. Smiljanić, I.
Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, “ Catalysis of hydrogen evolution
on Au (111) modified by spontaneously deposited Pd nanoislands,”
Electrocatalysis 3, 369–375 (2012).
https://doi.org/10.1007/s12678-012-0093-2246. S. Strbac, I. Srejic, and Z.
Rakocevic, “ Electrocatalysis of hydrogen evolution reaction on Au (111) by
spontaneously deposited iridium in acid solution,” J. Electrochem. Soc. 165(15),
J3335–J3341 (2018). https://doi.org/10.1149/2.0441815jes In 2011, Quaino et al.
combined theory and experiments to focus on the ensemble influence on different
Pd nanostructures decorated on Au (111), containing monolayer, clusters,
monomers, and rows.247247. P. Quaino, E. Santos, H. Wolfschmidt, M. Montero, and
U. Stimming, “ Theory meets experiment: Electrocatalysis of hydrogen
oxidation/evolution at Pd-Au nanostructures,” Catal. Today 177(1), 55–63 (2011).
https://doi.org/10.1016/j.cattod.2011.05.004 Remarkably, the activity of Pd/Au
(111) was considerably proliferated when decreasing the Pd coverage and Pd with
the nanostructure of small clusters in monoatomic height dimension, in which the
density of states showed the strongest shift towards the Fermi level, even more
than that in monolayer. Later, they continued to study the impact of successive
Pd layers on Au (111) for HER and reported less negative adsorption free energy
and lower barrier of Pd with two layers, thus showing a larger activity toward
HER.248248. P. Quaino and E. Santos, “ Hydrogen evolution reaction on palladium
multilayers deposited on Au (111): A theoretical approach,” Langmuir 31(2),
858–867 (2015). https://doi.org/10.1021/la503881y In a study published in the
last year, the authors, by means of the electrochemical scanning tunneling
microscopy (n-ECSTM) technology, found that the most active sites in
sub-monolayer Pd/Au (111) were located close to the boundary between Pd atoms
and Au.216216. Y. Liang, C. Csoklich, D. McLaughlin, O. Schneider, and A. S.
Bandarenka, “ Revealing active sites for hydrogen evolution at Pt and Pd atomic
layers on Au surfaces,” ACS Appl. Mater. Interfaces 11(13), 12476–12480 (2019).
https://doi.org/10.1021/acsami.8b22146 Besides, the significant enhancement of
the HER catalytic behavior in the Au (111) electrode with Rh overlayer (Rh/Au
(111)) was first predicted by theoretical results in 2011, and then was further
confirmed experimentally.249,250249. G. Soldano, E. N. Schulz, D. R. Salinas, E.
Santos, and W. Schmickler, “ Hydrogen electrocatalysis on overlayers of rhodium
over gold and palladium substrates-more active than platinum?,” Phys. Chem.
Chem. Phys. 13(36), 16437–16443 (2011). https://doi.org/10.1039/c1cp21565e250.
M. Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, “ Hydrogen
evolution on Au (111) catalyzed by rhodium nanoislands,” Electrochem. Commun.
28, 37–39 (2013). https://doi.org/10.1016/j.elecom.2012.12.009 These reports
have corroborated that this Rh/Au (111) electrode was highly active for the HER.
The high activity was deemed to be associated with a strong electronic synergism
between the two metals, which accelerated the different reaction pathways in
hydrogen-evolution mechanism and so boosted the overall reaction rate.
Subsequently, based on the XPS experimental results, this electronic effect was
indeed attested.251251. S. Štrbac, M. Smiljanić, and Z. Rakočević, “
Spontaneously deposited Rh on Au (111) observed by AFM and XPS: Electrocatalysis
of hydrogen evolution,” J. Electrochem. Soc. 163(12), D3027 (2016).
https://doi.org/10.1149/2.0041612jes Recently, Strbac et al. fully covered the
Au (111) surface with Ir by the simple and fast spontaneous deposition. This
composite electrode offered pronounced HER catalysis with respect to bare Au
(111), but still was inferior to the bare Ir(poly).246246. S. Strbac, I. Srejic,
and Z. Rakocevic, “ Electrocatalysis of hydrogen evolution reaction on Au (111)
by spontaneously deposited iridium in acid solution,” J. Electrochem. Soc.
165(15), J3335–J3341 (2018). https://doi.org/10.1149/2.0441815jes According to
the Strbac's team, HER catalysis was also investigated on the model Pd/Pt(poly)
electrode, which yielded the improved catalytic activity under alkaline
conditions in comparison with the bare Pt(poly).252252. M. Smiljanic, Z.
Rakocevic, A. Maksic, and S. Strbac, “ Hydrogen evolution reaction on platinum
catalyzed by palladium and rhodium nanoislands,” Electrochim. Acta 117(20),
336–343 (2014). https://doi.org/10.1016/j.electacta.2013.11.142 Meanwhile, the
study was extended to the similar Rh/Pt(poly) system, in which more excellent
HER catalytic performance than that of Pd/Pt(poly) was achieved and explained by
the larger susceptibility of the Rh deposit to the electronic interaction with
this Pt(poly) support. Furthermore, their recent work displayed the bimetallic
Ir/Pt(poly) electrode as an effective cathode for hydrogen production in
base.253253. S. Štrbac, M. Smiljanić, T. Wakelin, J. Potočnik, and Z. Rakočević,
“ Hydrogen evolution reaction on bimetallic Ir/Pt (poly) electrodes in alkaline
solution,” Electrochim. Acta 306(20), 18–27 (2019).
https://doi.org/10.1016/j.electacta.2019.03.100 In this catalyst, the
heterogeneity of surface active centers and the electron interplay between the
Ir and Pt in a close contact synergistically promoted the adsorption of the
H-related intermediates, thus which could effectively catalyze the HER.
Table III displays the comparison of the HER catalytic performance of various
representative non-Pt noble metal-based hybrids in the different media.
TABLE III. Performance of various representative non-Pt noble metal-based
hybrids.
Catalyst Electrolyte Loading (mg cm−2) Overpotential η10 (mV) Tafel slope (mV
dec−1) Stability References Porous Pd@Ru NRs 1 M KOH 0.051 30 30 3000 CV or −31
mV @ 12 h 149149. Y. Luo, X. Luo, G. Wu, Z. Li, G. Wang, B. Jiang, Y. Hu, T.
Chao, H. Ju, and J. Zhu, “ Mesoporous Pd@ Ru core-shell nanorods for hydrogen
evolution reaction in alkaline solution,” ACS Appl. Mater. Interfaces 10(40),
34147–34152 (2018). https://doi.org/10.1021/acsami.8b09988 Au75Rh25 decahedra
0.5 M H2SO4 1.96 μgRh cm−2 64.1 33.8 500 CV or −10 mA cm−2@2.8 h 154154. T.
Bian, B. Xiao, B. Sun, L. Huang, S. Su, Y. Jiang, J. Xiao, A. Yuan, H. Zhang,
and D. Yang, “ Local epitaxial growth of Au-Rh core-shell star-shaped decahedra:
A case for studying electronic and ensemble effects in hydrogen evolution
reaction,” Appl. Catal. B 263, 118255 (2020).
https://doi.org/10.1016/j.apcatb.2019.118255 Ag–Ni NWs 0.1 M KOH 0.12 197 84 −10
mA cm−2 @ 3 h 137137. C. Zhang, S. Liu, Z. Mao, X. Liang, and B. Chen, “ Ag-Ni
core-shell nanowires with superior electrocatalytic activity for alkaline
hydrogen evolution reaction,” J. Mater. Chem. A 5(32), 16646–16652 (2017).
https://doi.org/10.1039/C7TA04220E Pd/FeOx(OH)2 − 2x 0.1 M KOH 0.0254 ∼0 (onset)
131–162 … 153153. H. Liao, C. Wei, J. Wang, A. Fisher, T. Sritharan, Z. Feng,
and Z. J. Xu, “ A multisite strategy for enhancing the hydrogen evolution
reaction on a nano-Pd surface in alkaline media,” Adv. Energy Mater. 7(21),
1701129 (2017). https://doi.org/10.1002/aenm.201701129 NiAu/Au NPs 0.5 M H2SO4
0.068 7 (onset) 36 10 000 CV 160160. H. Lv, Z. Xi, Z. Chen, S. Guo, Y. Yu, W.
Zhu, Q. Li, X. Zhang, M. Pan, and G. Lu, “ A new core/shell NiAu/Au nanoparticle
catalyst with Pt-like activity for hydrogen evolution reaction,” J. Am. Chem.
Soc. 137(18), 5859–5862 (2015). https://doi.org/10.1021/jacs.5b01100 Ag@PdAg
nanocubes 0.5 M H2SO4 0.408 13.8 (η0) 70 5000 CV 162162. Y. Li, S. Chen, R.
Long, H. Ju, Z. Wang, X. Yu, F. Gao, Z. Cai, C. Wang, and Q. Xu, “ Near-surface
dilution of trace Pd atoms to facilitate Pd-H bond cleavage for giant
enhancement of electrocatalytic hydrogen evolution,” Nano Energy 34, 306–312
(2017). https://doi.org/10.1016/j.nanoen.2017.02.048 Pd@PtCu dodecahedron 0.5 M
H2SO4 15 μgPt cm−2 19 26.2 10 000 CV 163163. M. Bao, I. S. Amiinu, T. Peng, W.
Li, S. Liu, Z. Wang, Z. Pu, D. He, Y. Xiong, and S. Mu, “ Surface evolution of
PtCu alloy shell over Pd nanocrystals leads to superior hydrogen evolution and
oxygen reduction reactions,” ACS Energy Lett. 3(4), 940–945 (2018).
https://doi.org/10.1021/acsenergylett.8b00330 0.1 M KOH 60 … Pd–Pt
heterostructure 1 M KOH 12 μgPt cm−2 71 31 −70 mV @ 2.22 h 164164. J. Fan, K.
Qi, L. Zhang, H. Zhang, S. Yu, and X. Cui, “ Engineering Pt/Pd interfacial
electronic structures for highly efficient hydrogen evolution and alcohol
oxidation,” ACS Appl. Mater. Interfaces 9(21), 18008–18014 (2017).
https://doi.org/10.1021/acsami.7b05290 W+Ru 0.5 M H2SO4 5.6 μgRu cm−2 114 μgW
cm−2 85 46 −10 mA cm−2 @ 24 h 165165. U. Joshi, S. Malkhandi, Y. Ren, T. L. Tan,
S. Y. Chiam, and B. S. Yeo, “ Ruthenium-tungsten composite catalyst for the
efficient and contamination-resistant electrochemical evolution of hydrogen,”
ACS Appl. Mater. Interfaces 10(7), 6354–6360 (2018).
https://doi.org/10.1021/acsami.7b17970 w-Au@MoS2 0.5 M H2SO4 … 120 52.9 10 h CV
186186. Y. Li, M. B. Majewski, S. M. Islam, S. Hao, A. A. Murthy, J. G.
DiStefano, E. D. Hanson, Y. Xu, C. Wolverton, and M. G. Kanatzidis, “
Morphological engineering of winged Au@MoS2 heterostructures for
electrocatalytic hydrogen evolution,” Nano Lett. 18(11), 7104–7110 (2018).
https://doi.org/10.1021/acs.nanolett.8b03109 Ir/MoS2 1 M KOH 0.285 44 32 9000 CV
or −44 mV @ 18 h 190190. S. Wei, X. Cui, Y. Xu, B. Shang, Q. Zhang, L. Gu, X.
Fan, L. Zheng, C. Hou, and H. Huang, “ Iridium-triggered phase transition of
MoS2 nanosheets boosts overall water splitting in alkaline media,” ACS Energy
Lett. 4(1), 368–374 (2019). https://doi.org/10.1021/acsenergylett.8b01840 1T
MoS2-Au/Pd 0.5 M H2SO4 0.214 50 (η0) 63 1000 CV 187187. B. Shang, X. Cui, L.
Jiao, K. Qi, Y. Wang, J. Fan, Y. Yue, H. Wang, Q. Bao, and X. Fan, “
Lattice-mismatch-induced ultrastable 1T-phase MoS2-Pd/Au for plasmon-enhanced
hydrogen evolution,” Nano Lett. 19(5), 2758–2764 (2019).
https://doi.org/10.1021/acs.nanolett.8b04104 Ru-MoS2/CC 0.5 M H2SO4 46 μgRu cm-2
61 … −10 mA cm−2 @ 20 h 195195. D. Wang, Q. Li, C. Han, Z. Xing, and X. Yang, “
Single-atom ruthenium based catalyst for enhanced hydrogen evolution,” Appl.
Catal. B 249(15), 91–97 (2019). https://doi.org/10.1016/j.apcatb.2019.02.059 1 M
PBS 114 … −10 mA cm−2 @ 10 h 1 M KOH 41 114 −10 mA cm−2 @ 10 h NiCo2S4/Pd 0.5 M
H2SO4 0.306 87 70 −10 mA cm−2 @ 10 h 197197. G. Sheng, J. Chen, Y. Li, H. Ye, Z.
Hu, X.-Z. Fu, R. Sun, W. Huang, and C.-P. Wong, “ Flowerlike NiCo2S4 hollow
sub-microspheres with mesoporous nanoshells support Pd nanoparticles for
enhanced hydrogen evolution reaction electrocatalysis in both acidic and
alkaline conditions,” ACS Appl. Mater. Interfaces 10(26), 22248–22256 (2018).
https://doi.org/10.1021/acsami.8b05427 1 M KOH 83 123 Ag@Cu2O/CF 1 M KOH … 108
58 −200 mV @ 20 h 198198. C. Song, Z. Zhao, X. Sun, Y. Zhou, Y. Wang, and D.
Wang, “ In situ growth of Ag nanodots decorated Cu2O porous nanobelts networks
on copper foam for efficient HER electrocatalysis,” Small 15(29), 1804268
(2019). https://doi.org/10.1002/smll.201804268 Ag-WO3 (0.8) 0.5 M H2SO4 0.708
207 52.4 2000 CV 199199. J. Ma, Z. Ma, B. Liu, S. Wang, R. Ma, and C. Wang, “
Composition of Ag-WO3 core-shell nanostructures as efficient electrocatalysts
for hydrogen evolution reaction,” J. Solid State Chem. 271, 246–252 (2019).
https://doi.org/10.1016/j.jssc.2018.12.020 AL-Pt/Pd3Pb 0.5 M H2SO4 40.8 μgPt+Pd
cm−2 13.8 18 10 000 CV or −14 mV @ 25 h 200200. Y. Yao, X.-K. Gu, D. He, Z. Li,
W. Liu, Q. Xu, T. Yao, Y. Lin, H.-J. Wang, and C. Zhao, “ Engineering the
electronic structure of submonolayer Pt on intermetallic Pd3Pb via charge
transfer boosts the hydrogen evolution reaction,” J. Am. Chem. Soc. 141(51),
19964–19968 (2019). https://doi.org/10.1021/jacs.9b09391 Co(OH)2–Au–Ni(OH)2 1 M
NaOH … 200 92 −5 mA cm−2 @ 24 h 201201. U. K. Sultana, J. D. Riches, and A. P.
O'Mullane, “ Gold doping in a layered Co-Ni hydroxide system via galvanic
replacement for overall electrochemical water splitting,” Adv. Funct. Mater.
28(43), 1804361 (2018). https://doi.org/10.1002/adfm.201804361 Au–Ag NCs/rGO 0.5
M H2SO4 … 10 (η0) 39 10 000 CV 3737. Y. Qin, X. Dai, X. Zhang, X. Huang, H. Sun,
D. Gao, Y. Yu, P. Zhang, Y. Jiang, and H. Zhuo, “ Microwave-assisted synthesis
of multiply-twinned Au-Ag nanocrystals on reduced graphene oxide for high
catalytic performance towards hydrogen evolution reaction,” J. Mater. Chem. A
4(10), 3865–3871 (2016). https://doi.org/10.1039/C5TA10428A Ir_VG 0.5 M H2SO4 50
μgIr cm−2 47 43 1000 CV 221221. S. B. Roy, K. Akbar, J. H. Jeon, S.-K. Jerng, L.
Truong, K. Kim, Y. Yi, and S.-H. Chun, “ Iridium on vertical graphene as an
all-round catalyst for robust water splitting reactions,” J. Mater. Chem. A
7(36), 20590–20596 (2019). https://doi.org/10.1039/C9TA07388D 1 M KOH 17 29 Pd
NPs@N-CNTs 0.5 M H2SO4 0.285 32 (η100) 33 −0.25 V @2.78 h 222222. S. Zhou, X.
Chen, P. Yu, F. Gao, and L. Mao, “ Nitrogen-doped carbon nanotubes as an
excellent substrate for electroless deposition of Pd nanoparticles with a high
efficiency toward the hydrogen evolution reaction,” Electrochem. Commun. 90,
91–95 (2018). https://doi.org/10.1016/j.elecom.2018.04.015 PAH@Rh-NSNSs/CNT 0.5
M H2SO4 52 μgRh cm−2 5 30 1000 CV 225225. J. Bai, S.-H. Xing, Y.-Y. Zhu, J.-X.
Jiang, J.-H. Zeng, and Y. Chen, “ Polyallylamine-Rh nanosheet
nanoassemblies-carbon nanotubes organic-inorganic nanohybrids: A electrocatalyst
superior to Pt for the hydrogen evolution reaction,” J. Power Sources 385(1),
32–38 (2018). https://doi.org/10.1016/j.jpowsour.2018.03.022 Rh NP/C 1 M KOH
0.589 7 19 1000 CV 127127. Q. Wang, M. Ming, S. Niu, Y. Zhang, G. Fan, and J. S.
Hu, “ Scalable solid-state synthesis of highly dispersed uncapped metal (Rh, Ru,
Ir) nanoparticles for efficient hydrogen evolution,” Adv. Energy Mater. 8(31),
1801698 (2018). https://doi.org/10.1002/aenm.201801698 Ru NP/C 69 (η50) 33 Ir
NP/C 109 (η50) 42 Rh NP/PC 1 M KOH 0.6 33 128128. M. Ming, Y. Zhang, C. He, L.
Zhao, S. Niu, G. Fan, and J. S. Hu, “ Room-temperature sustainable synthesis of
selected platinum group metal (PGM = Ir, Rh, and Ru) nanocatalysts
well-dispersed on porous carbon for efficient hydrogen evolution and oxidation,”
Small 15(49), 1903057 (2019). https://doi.org/10.1002/smll.201903057 0.5 M H2SO4
21 34 1000 CV Ru NP/PC 1 M KOH 30 0.5 M H2SO4 63 63 Ir NP/PC 1 M KOH 110 0.5 M
H2SO4 30 35 Pd0/GDY 0.5 M H2SO4 0.447 55 47 1000 CV 223223. H. Yu, Y. Xue, B.
Huang, L. Hui, C. Zhang, Y. Fang, Y. Liu, Y. Zhao, Y. Li, and H. Liu, “
Ultrathin nanosheet of graphdiyne-supported palladium atom catalyst for
efficient hydrogen production,” iScience 11(25), 31–41 (2019).
https://doi.org/10.1016/j.isci.2018.12.006 Ru@SC-CQDs 0.5 M H2SO4 0.42 59 57
5000 CV or initial −10 mA cm−2 @ 100 h 229229. Y. Liu, Y. Yang, Z. Peng, Z. Liu,
Z. Chen, L. Shang, S. Lu, and T. Zhang, “ Self-crosslinking carbon dots loaded
ruthenium dots as an efficient and super-stable hydrogen production
electrocatalyst at all pH values,” Nano Energy 65, 104023 (2019).
https://doi.org/10.1016/j.nanoen.2019.104023 1 M PBS 66 158 1 M KOH 29 57 Au@NC
0.5 M H2SO4 0.357 54.1 (η1) 76.8 1000 CV or −300 mV @ 20 h 217217. W. Zhou, T.
Xiong, C. Shi, J. Zhou, K. Zhou, N. Zhu, L. Li, Z. Tang, and S. Chen, “
Bioreduction of precious metals by microorganism: Efficient Gold@N-doped carbon
electrocatalysts for the hydrogen evolution reaction,” Angew. Chem., Int. Ed.
55(29), 8416–8420 (2016). https://doi.org/10.1002/anie.201602627 IrHNC 0.5 M
H2SO4 18 μgIr cm−2 4.5 … … 203203. F. Li, G.-F. Han, H.-J. Noh, J.-P. Jeon, I.
Ahmad, S. Chen, C. Yang, Y. Bu, Z. Fu, and Y. Lu, “ Balancing hydrogen
adsorption/desorption by orbital modulation for efficient hydrogen evolution
catalysis,” Nat. Commun. 10, 4060 (2019).
https://doi.org/10.1038/s41467-019-12012-z RuNi–NCNFs 0.5 M H2SO4 0.612 23 29
5500 CV or −62 mV @ 12 h 228228. M. Li, H. Wang, W. Zhu, W. Li, C. Wang, and X.
Lu, “ RuNi nanoparticles embedded in N-doped carbon nanofibers as a robust
bifunctional catalyst for efficient overall water splitting,” Adv. Sci. 7(2),
1901833 (2020). https://doi.org/10.1002/advs.201901833 1 M KOH 35 30 6000 CV or
−40 mV @ 12 h RuCo@NC 1 M KOH 0.275 28 31 10 000 CV 5858. J. Su, Y. Yang, G.
Xia, J. Chen, P. Jiang, and Q. Chen, “ Ruthenium-cobalt nanoalloys encapsulated
in nitrogen-doped graphene as active electrocatalysts for producing hydrogen in
alkaline media,” Nat. Commun. 8, 14969 (2017).
https://doi.org/10.1038/ncomms14969 Pd/NG 0.5 M H2SO4 0.212 199 ∼80 … 224224. K.
Guo, L. J. Rowland, L. H. Isherwood, G. Glodan, and A. Baidak, “ Photon-induced
synthesis of ultrafine metal nanoparticles on graphene as electrocatalysts:
Impact of functionalization and doping,” J. Mater. Chem. A 8(2), 714–723 (2020).
https://doi.org/10.1039/C9TA10518B Ru NCs/BNG 1 M KOH 0.707 14 28.9 2000 CV or
−10 mA cm−2 @ 17 h 236236. S. Ye, F. Luo, T. Xu, P. Zhang, H. Shi, S. Qin, J.
Wu, C. He, X. Ouyang, and Q. Zhang, “ Boosting the alkaline hydrogen evolution
of Ru nanoclusters anchored on B/N-doped graphene by accelerating water
dissociation,” Nano Energy 68, 104301 (2020).
https://doi.org/10.1016/j.nanoen.2019.104301 Au-aerogel–CNx 0.5 M H2SO4 0.13
mgAu cm−2 30 (η0) 53 10 000 CV or −0.15 V @ 10 h 237237. M. K. Kundu, T.
Bhowmik, and S. Barman, “ Gold aerogel supported on graphitic carbon nitride: An
efficient electrocatalyst for oxygen reduction reaction and hydrogen evolution
reaction,” J. Mater. Chem. A 3(46), 23120–23135 (2015).
https://doi.org/10.1039/C5TA06740E Pd–CNx 0.5 M H2SO4 43 μgPd cm−2 55 35 10 000
CV or −60 mV @ 100 h 230230. T. Bhowmik, M. K. Kundu, and S. Barman, “ Palladium
nanoparticle-graphitic carbon nitride porous synergistic catalyst for hydrogen
evolution/oxidation reactions over a broad range of pH and correlation of its
catalytic activity with measured hydrogen binding energy,” ACS Catal. 6(3),
1929–1941 (2016). https://doi.org/10.1021/acscatal.5b02485 0.5 M KOH 180 (η5)
150 … C3N4–Ru 0.5 M H2SO4 0.153 140 57 1000 CV 238238. Y. Peng, B. Lu, L. Chen,
N. Wang, J. E. Lu, Y. Ping, and S. Chen, “ Hydrogen evolution reaction catalyzed
by ruthenium ion-complexed graphitic carbon nitride nanosheets,” J. Mater. Chem.
A 5(34), 18261–18269 (2017). https://doi.org/10.1039/C7TA03826G Rh/Si NWs 0.5 M
H2SO4 0.193 44 (onset) 24 −0.1/0.3 V @ 138.9 h 212212. L. Zhu, H. Lin, Y. Li, F.
Liao, Y. Lifshitz, M. Sheng, S.-T. Lee, and M. Shao, “ A rhodium/silicon
co-electrocatalyst design concept to surpass platinum hydrogen evolution
activity at high overpotentials,” Nat. Commun. 7, 12272 (2016).
https://doi.org/10.1038/ncomms12272 Rh–Ag–Si 0.5 M H2SO4 0.140 120 51 −0.25 V @
12 h 211211. B. Jiang, Y. Sun, F. Liao, W. Shen, H. Lin, H. Wang, and M. Shao, “
Rh-Ag-Si ternary composites: Highly active hydrogen evolution electrocatalysts
over Pt-Ag-Si,” J. Mater. Chem. A 5(4), 1623–1628 (2017).
https://doi.org/10.1039/C6TA09619K Ir/Si NWs 0.5 M H2SO4 0.339 22 20 −10 mA cm−2
@ 13.9 h 214214. M. Sheng, B. Jiang, B. Wu, F. Liao, X. Fan, H. Lin, Y. Li, Y.
Lifshitz, S.-T. Lee, and M. Shao, “ Approaching the volcano top: Iridium/silicon
nanocomposites as efficient electrocatalysts for the hydrogen evolution
reaction,” ACS Nano 13(3), 2786–2794 (2019).
https://doi.org/10.1021/acsnano.8b07572
D. Other modulation strategies
Apart from various design strategies mentioned above, several other approaches
can also alter the catalytic activity of the non-Pt NMNs. The materials with
identical chemical composition but different crystalline structures or exposed
active facets displayed different atomic coordinations and electronic
distributions and thus had a great effect on the HER catalytic
activity.12,254–25912. J. Yu, Q. He, G. Yang, W. Zhou, Z. Shao, and M. Ni, “
Recent advances and prospective in ruthenium-based materials for electrochemical
water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b02457254. Y. Zheng, Y. Jiao, Y. Zhu, L. H.
Li, Y. Han, Y. Chen, M. Jaroniec, and S.-Z. Qiao, “ High electrocatalytic
hydrogen evolution activity of an anomalous ruthenium catalyst,” J. Am. Chem.
Soc. 138(49), 16174–16181 (2016). https://doi.org/10.1021/jacs.6b11291255. Y.
Yao, D. S. He, Y. Lin, X. Feng, X. Wang, P. Yin, X. Hong, G. Zhou, Y. Wu, and Y.
Li, “ Modulating fcc and hcp ruthenium on the surface of palladium-copper alloy
through tunable lattice mismatch,” Angew. Chem., Int. Ed. 128(18), 5591–5595
(2016). https://doi.org/10.1002/ange.201601016256. W.-Z. Li, J.-X. Liu, J. Gu,
W. Zhou, S.-Y. Yao, R. Si, Y. Guo, H.-Y. Su, C.-H. Yan, and W.-X. Li, “ Chemical
insights into the design and development of face-centered cubic ruthenium
catalysts for Fischer–Tropsch synthesis,” J. Am. Chem. Soc. 139(6), 2267–2276
(2017). https://doi.org/10.1021/jacs.6b10375257. S. Sarkar and S. C. Peter, “ An
overview on Pd-based electrocatalysts for the hydrogen evolution reaction,”
Inorg. Chem. Front. 5(9), 2060–2080 (2018).
https://doi.org/10.1039/C8QI00042E258. A. Zalineeva, S. Baranton, C. Coutanceau,
and G. Jerkiewicz, “ Octahedral palladium nanoparticles as excellent hosts for
electrochemically adsorbed and absorbed hydrogen,” Sci. Adv. 3(2), e1600542
(2017). https://doi.org/10.1126/sciadv.1600542259. X. Huang, S. Li, Y. Huang, S.
Wu, X. Zhou, S. Li, C. L. Gan, F. Boey, C. A. Mirkin, and H. Zhang, “ Synthesis
of hexagonal close-packed gold nanostructures,” Nat. Commun. 2, 292 (2011).
https://doi.org/10.1038/ncomms1291 Ru metal with a face-centered cubic (fcc)
structure has been demonstrated to deliver higher HER activity than that with a
hexagonal close packed (hcp) structure and yet the fcc-structured Ru crystal
tended to be obtained through a relatively complex or peculiar synthetic route,
which has been well summarized in our previous study and thereby will not be
discussed in detail here.1212. J. Yu, Q. He, G. Yang, W. Zhou, Z. Shao, and M.
Ni, “ Recent advances and prospective in ruthenium-based materials for
electrochemical water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b02457 Unlike this, other noble metals like
Rh, Pd, Ag, Ir, and Au normally existed with the stable fcc phase, rather than
the hcp phase.136,259136. J. Yang, Y. Ji, Q. Shao, N. Zhang, Y. Li, and X.
Huang, “ A universal strategy to metal wavy nanowires for efficient
electrochemical water splitting at pH-universal conditions,” Adv. Funct. Mater.
28(41), 1803722 (2018). https://doi.org/10.1002/adfm.201803722259. X. Huang, S.
Li, Y. Huang, S. Wu, X. Zhou, S. Li, C. L. Gan, F. Boey, C. A. Mirkin, and H.
Zhang, “ Synthesis of hexagonal close-packed gold nanostructures,” Nat. Commun.
2, 292 (2011). https://doi.org/10.1038/ncomms1291 Interestingly, the
nanostructure sometimes can manipulate the phase structure. For example,
hierarchical Ru nanotubes were reported to display a stable fcc structure, while
ultrathin Au nanosheets possessed an anomalous hcp phase.259259. X. Huang, S.
Li, Y. Huang, S. Wu, X. Zhou, S. Li, C. L. Gan, F. Boey, C. A. Mirkin, and H.
Zhang, “ Synthesis of hexagonal close-packed gold nanostructures,” Nat. Commun.
2, 292 (2011). https://doi.org/10.1038/ncomms1291 The amorphous phase possesses
isotropic properties and disordered structures, which can enable a wide exposure
of abundant active sites.260,261260. Y. Guo, T. Park, J. W. Yi, J. Henzie, J.
Kim, Z. Wang, B. Jiang, Y. Bando, Y. Sugahara, and J. Tang, “ Nanoarchitectonics
for transition-metal-sulfide-based electrocatalysts for water splitting,” Adv.
Mater. 31(17), 1807134 (2019). https://doi.org/10.1002/adma.201807134261. J. Yu,
Y. Zhong, X. Wu, J. Sunarso, M. Ni, W. Zhou, and Z. Shao, “ Bifunctionality from
synergy: CoP nanoparticles embedded in amorphous CoOx nanoplates with
heterostructures for highly efficient water electrolysis,” Adv. Sci. 5(9),
1800514 (2018). https://doi.org/10.1002/advs.201800514 Consequently, the
amorphous materials are highly likely to possess an outstanding electrocatalytic
performance. In a recent report, Li et al. declared that a nanohybrid,
consisting of amorphous ruthenium-sulfide nanoparticles and sulfur-doped
graphene oxide (RuSx/S-GO), acted as a Pt-like electrocatalyst for hydrogen
production, requiring low overpotentials of 31, 46, and 58 mV to reach a 10 mA
cm−2 benchmark current density under the acidic, neutral, and alkaline
conditions, respectively, as well as robust durability.9494. P. Li, X. Duan, S.
Wang, L. Zheng, Y. Li, H. Duan, Y. Kuang, and X. Sun, “ Amorphous
ruthenium-sulfide with isolated catalytic sites for Pt-like electrocatalytic
hydrogen production over whole pH range,” Small 15(46), 1904043 (2019).
https://doi.org/10.1002/smll.201904043 A combination of experimental
characterization and theoretical simulation evidenced that the isolated Ru
single atoms in the RuSx amorphous structure were the active sites for the HER
process. Moreover, it was manifested that the tight coupling between small RuSx
nanoparticles and the S-GO support played a critical role in stabilizing the
catalytic material. Likewise, amorphous RuTe2 porous nanorods were also attained
by Huang's group and demonstrated a significant improvement of HER catalytic
behavior relative to its crystalline counterparts under both acidic and alkaline
conditions.9797. J. Wang, L. Han, B. Huang, Q. Shao, H. L. Xin, and X. Huang, “
Amorphization activated ruthenium-tellurium nanorods for efficient water
splitting,” Nat. Commun. 10, 5692 (2019).
https://doi.org/10.1038/s41467-019-13519-1
Regarding exposed facet control, it is generally realized by adjusting the
particle morphologies.135,257,258135. T.-R. Kuo, Y.-C. Lee, H.-L. Chou, M. G.
Swathi, C.-Y. Wei, C.-Y. Wen, Y.-H. Chang, X.-Y. Pan, and D.-Y. Wang, “
Plasmon-enhanced hydrogen evolution on specific facet of silver nanocrystals,”
Chem. Mater. 31(10), 3722–3728 (2019).
https://doi.org/10.1021/acs.chemmater.9b00652257. S. Sarkar and S. C. Peter, “
An overview on Pd-based electrocatalysts for the hydrogen evolution reaction,”
Inorg. Chem. Front. 5(9), 2060–2080 (2018).
https://doi.org/10.1039/C8QI00042E258. A. Zalineeva, S. Baranton, C. Coutanceau,
and G. Jerkiewicz, “ Octahedral palladium nanoparticles as excellent hosts for
electrochemically adsorbed and absorbed hydrogen,” Sci. Adv. 3(2), e1600542
(2017). https://doi.org/10.1126/sciadv.1600542 For instance, Pd nanoparticles
(NPs) with different shapes, such as spheres and octahedra, as well as simple
nanocubes, are solely enclosed by the (111) and (100) facets.257257. S. Sarkar
and S. C. Peter, “ An overview on Pd-based electrocatalysts for the hydrogen
evolution reaction,” Inorg. Chem. Front. 5(9), 2060–2080 (2018).
https://doi.org/10.1039/C8QI00042E This aspect has been well discussed in Sec.
IV B. In addition, the novel worm-like Ir-oriented nanocrystalline assemblies
(Ir ONAs) with more exposed low-index crystalline planes were also fabricated
and featured superior HER activity in alkaline electrolytes compared to the
nanoparticle counterparts (Ir NPs).262262. F. Yang, L. Fu, G. Cheng, S. Chen,
and W. Luo, “ Ir-oriented nanocrystalline assemblies with high activity for
hydrogen oxidation/evolution reactions in an alkaline electrolyte,” J. Mater.
Chem. A 5(44), 22959–22963 (2017). https://doi.org/10.1039/C7TA07635E Such
results could be partly ascribed to the fact that the quasi-1D nanostructure
provided more low-index facet atoms with lower hydrogen binding energy.
V. NEW TRENDS IN THE ELECTROCATALYTIC HER
Section:
ChooseTop of pageABSTRACTI. INTRODUCTIONII. FUNDAMENTALS OF THE H...III. BRIEF
OVERVIEW OF TH...IV. CONSTRUCTING ROBUST N...V. NEW TRENDS IN THE ELEC... <<VI.
CONCLUSIONS AND OUTLO...Choose
In this section, we briefly discuss the development of new trends in
electrocatalytic hydrogen production, including pH universality and
bifunctionality. Relative to other non-noble metal catalysts, the design of
non-Pt NMNs is highly suitable for such trends.
A. pH universality
Of note, different electrolytic devices necessitate varied operating
conditions.66. J. Wang, F. Xu, H. Jin, Y. Chen, and Y. Wang, “ Non-noble
metal-based carbon composites in hydrogen evolution reaction: Fundamentals to
applications,” Adv. Mater. 29(14), 1605838 (2017).
https://doi.org/10.1002/adma.201605838 Proton exchange membrane (PEM)-related
electrolyzers need active and robust electrocatalysts that can operate in acidic
media, while some water–alkali and chloro–alkali electrolysis cells typically
require alkaline-stable HER catalysts. In some microbial electrolysis units, the
operating environment is the neutral electrolyte. Thus, exploiting pH-universal
HER catalytic materials could enormously broaden the application prospects. More
significantly, given that most of the best electrocatalysts for the OER function
well only in alkaline or neutral solution, the pH-compatible anodic
electrocatalysts in the overall water splitting are relatively infrequent.
Competent HER catalysts operating at all pH values offer the great chance to
cooperate with OER catalytic materials for achieving the overall water
splitting. As such, it is highly desirable but challenging to find versatile and
efficient HER electrocatalysts that function well in a large window of solution
pHs. Noble metals, due to their decent activity for electrocatalysis and being
able to withstand extremely harsh conditions, like a strong acid or base, hold a
great promise for pH-universal HER applications. Notwithstanding, not all the
noble metal-based materials can adapt to a wide pH range. However, compared to
active transition metals, noble metal-based materials have much more
possibilities for the pH-universal HER with superior performance. So far, a
plethora of non-Pt NMNs, such as IrW ND, RuIrOx, PdP2@CB, Li-IrSe2, Ru-MoS2/CC,
Ru@SC-CQDs, etc., were shown to have splendid catalytic activity and durability
for the HER over a wide range of pH values.62,69,92,99,195,22962. F. Lv, J.
Feng, K. Wang, Z. Dou, W. Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “
Iridium-tungsten alloy nanodendrites as pH-universal water-splitting
electrocatalysts,” ACS Cent. Sci. 4(9), 1244–1252 (2018).
https://doi.org/10.1021/acscentsci.8b0042669. Z. Zhuang, Y. Wang, C.-Q. Xu, S.
Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S. Lu, “
Three-dimensional open nano-netcage electrocatalysts for efficient pH-universal
overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-092. F. Luo, Q. Zhang, X. Yu, S. Xiao,
Y. Ling, H. Hu, L. Guo, Z. Yang, L. Huang, and W. Cai, “ Palladium phosphide as
a stable and efficient electrocatalyst for overall water splitting,” Angew.
Chem., Int. Ed. 57(45), 14862–14867 (2018).
https://doi.org/10.1002/anie.20181010299. T. Zheng, C. Shang, Z. He, X. Wang, C.
Cao, H. Li, R. Si, B. Pan, S. Zhou, and J. Zeng, “ Intercalated iridium
diselenide electrocatalysts for efficient pH-universal water splitting,” Angew.
Chem., Int. Ed. 131(41), 14906–14911 (2019).
https://doi.org/10.1002/ange.201909369195. D. Wang, Q. Li, C. Han, Z. Xing, and
X. Yang, “ Single-atom ruthenium based catalyst for enhanced hydrogen
evolution,” Appl. Catal. B 249(15), 91–97 (2019).
https://doi.org/10.1016/j.apcatb.2019.02.059229. Y. Liu, Y. Yang, Z. Peng, Z.
Liu, Z. Chen, L. Shang, S. Lu, and T. Zhang, “ Self-crosslinking carbon dots
loaded ruthenium dots as an efficient and super-stable hydrogen production
electrocatalyst at all pH values,” Nano Energy 65, 104023 (2019).
https://doi.org/10.1016/j.nanoen.2019.104023 A summary of them is given in Table
IV, some of which have been minutely introduced in the fourth section. Recently,
Mahmood et al. presented ultrafine Ir nanoparticles uniformly embedded in a 3D
cage-like organic network (Ir@CON) for the pH-universal HER.219219. J. Mahmood,
M. A. R. Anjum, S. H. Shin, I. Ahmad, H. J. Noh, S. J. Kim, H. Y. Jeong, J. S.
Lee, and J. B. Baek, “ Encapsulating iridium nanoparticles inside a 3D cage-like
organic network as an efficient and durable catalyst for the hydrogen evolution
reaction,” Adv. Mater. 30(52), 1805606 (2018).
https://doi.org/10.1002/adma.201805606 The Ir@CON sample delivered prominent
catalytic properties, with reaching 10 mA cm−2 by the overpotentials of 13.6 and
13.5 mV and achieving the TOF values of 0.66 and 0.2 H2 s−1 at 25 mV in acidic
and alkaline solutions, respectively. Construction of a 3D CON structure not
only offered a large surface area, but also enabled a conductive platform that
uniformly and stably anchored Ir nanoparticles to maximize active sites.
Pleasingly, N, S-coordinated Ru single atoms supported on titanium carbide
(Ti3C2Tx) MXene matrixes (RuSA–N–S–Ti3C2Tx) were further designed, which could
apply to the HER with super behavior in a broad pH range.263263. V. Ramalingam,
P. Varadhan, H. C. Fu, H. Kim, D. Zhang, S. Chen, L. Song, D. Ma, Y. Wang, and
H. N. Alshareef, “ Heteroatom‐mediated interactions between ruthenium single
atoms and an MXene support for efficient hydrogen evolution,” Adv. Mater.
31(48), 1903841 (2019). https://doi.org/10.1002/adma.201903841 The coordination
of Ru single atoms and N/S sites on Ti3C2Tx induced matrices optimized the
electronic structure, thus affording more suitable Gibbs hydrogen adsorption
energy.
TABLE IV. Performance of various representative pH-universal non-Pt NMN
electrocatalysts.
Catalyst Electrolyte Loading (mg cm−2) Overpotential η10 (mV) Tafel slope (mV
dec−1) Stability References Pd66Ag17Al17 1 M KOH … 16.8 56 10 000 CV 3535. R.-Q.
Yao, Y.-T. Zhou, H. Shi, Q.-H. Zhang, L. Gu, Z. Wen, X.-Y. Lang, and Q. Jiang, “
Nanoporous palladium-silver surface alloys as efficient and pH-universal
catalysts for the hydrogen evolution reaction,” ACS Energy Lett. 4(6), 1379–1386
(2019). https://doi.org/10.1021/acsenergylett.9b00845 0.5 M H2SO4 … ∼35 26
30 000 CV PtRu 0.5 M H2SO4 13.9 μgRu cm−2 8 25 10 000 CV or −15/40/30 mV @10 h
4444. L. Li, G. Zhang, B. Wang, T. Yang, and S. Yang, “ Electrochemical
formation of PtRu bimetallic nanoparticles for highly efficient and pH-universal
hydrogen evolution reaction,” J. Mater. Chem. A 8(4), 2090–2098 (2020).
https://doi.org/10.1039/C9TA12300H 1 M PBS 25 36 1 M KOH 19 28 np-Cu53Ru47 1 M
KOH 0.306 15 30 −15 mV @ 27 h −40 mV @ 27 h 6161. Q. Wu, M. Luo, J. Han, W.
Peng, Y. Zhao, D. Chen, M. Peng, J. Liu, F. M. de Groot, and Y. Tan, “
Identifying electrocatalytic sites of the nanoporous copper-ruthenium alloy for
hydrogen evolution reaction in alkaline electrolyte,” ACS Energy Lett. 5(1),
192–199 (2020). https://doi.org/10.1021/acsenergylett.9b02374 1 M PBS 41 35 IrW
ND 0.1 M HClO4 10.2 μgIr cm−2 12 … 1000 CV 6262. F. Lv, J. Feng, K. Wang, Z.
Dou, W. Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “ Iridium-tungsten
alloy nanodendrites as pH-universal water-splitting electrocatalysts,” ACS Cent.
Sci. 4(9), 1244–1252 (2018). https://doi.org/10.1021/acscentsci.8b00426 0.1 M
KOH 29 … RuIrOx 0.5 M H2SO4 0.833 12 21 3000 CV 6969. Z. Zhuang, Y. Wang, C.-Q.
Xu, S. Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S. Lu, “
Three-dimensional open nano-netcage electrocatalysts for efficient pH-universal
overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-0 1 M KOH 13 23 w-Rh2P NS 0.1 M HClO4
0.0123 15.8 29.9 1000 CV 8484. K. Wang, B. Huang, F. Lin, F. Lv, M. Luo, P.
Zhou, Q. Liu, W. Zhang, C. Yang, and Y. Tang, “ Wrinkled Rh2P nanosheets as
superior pH-universal electrocatalysts for hydrogen evolution catalysis,” Adv.
Energy Mater. 8(27), 1801891 (2018). https://doi.org/10.1002/aenm.201801891 0.1
M PBS 21.9 78.4 0.1 M KOH 18.3 61.5 L-RuP 0.5 M H2SO4 0.185 19 37 −10 mA cm−2 @
200 h 8787. J. Yu, Y. Guo, S. She, S. Miao, M. Ni, W. Zhou, M. Liu, and Z. Shao,
“ Bigger is surprisingly better: Agglomerates of larger RuP nanoparticles
outperform benchmark Pt nanocatalysts for the hydrogen evolution reaction,” Adv.
Mater. 30(39), 1800047 (2018). https://doi.org/10.1002/adma.201800047 1 M PBS 95
54 1 M KOH 18 34 PdP2@CB 0.5 M H2SO4 0.285 27.5 29.5 5000 CV or −27.5/84.6/35.4
mV @ 10 h 9292. F. Luo, Q. Zhang, X. Yu, S. Xiao, Y. Ling, H. Hu, L. Guo, Z.
Yang, L. Huang, and W. Cai, “ Palladium phosphide as a stable and efficient
electrocatalyst for overall water splitting,” Angew. Chem., Int. Ed. 57(45),
14862–14867 (2018). https://doi.org/10.1002/anie.201810102 1 M PBS 84.6 72.3 1 M
KOH 35.4 42.1 IrP2@NC 0.5 M H2SO4 0.7 8 28 1000 CV 9191. Z. Pu, J. Zhao, I. S.
Amiinu, W. Li, M. Wang, D. He, and S. Mu, “ A universal synthesis strategy for
P-rich noble metal diphosphide-based electrocatalysts for the hydrogen evolution
reaction,” Energy Environ. Sci. 12(3), 952–957 (2019).
https://doi.org/10.1039/C9EE00197B 1 M KOH 28 50 RuSx/S-GO 0.5 M H2SO4 1 31 40
Initial −50 mA cm−2 @ 12 h 9494. P. Li, X. Duan, S. Wang, L. Zheng, Y. Li, H.
Duan, Y. Kuang, and X. Sun, “ Amorphous ruthenium-sulfide with isolated
catalytic sites for Pt-like electrocatalytic hydrogen production over whole pH
range,” Small 15(46), 1904043 (2019). https://doi.org/10.1002/smll.201904043 1 M
PBS 46 39 1 M KOH 58 56 Li-IrSe2 0.5 M H2SO4 0.25 55 … −64/173/105 mV @ 10 h
9999. T. Zheng, C. Shang, Z. He, X. Wang, C. Cao, H. Li, R. Si, B. Pan, S. Zhou,
and J. Zeng, “ Intercalated iridium diselenide electrocatalysts for efficient
pH-universal water splitting,” Angew. Chem., Int. Ed. 131(41), 14906–14911
(2019). https://doi.org/10.1002/ange.201909369 1 M PBS 120 … 1 M KOH 72 … RuB2
0.5 M H2SO4 0.281 18 38.9 −10 mA cm−2 @ 50 h 7272. Q. Li, X. Zou, X. Ai, H.
Chen, L. Sun, and X. Zou, “ Revealing activity trends of metal diborides toward
pH-universal hydrogen evolution electrocatalysts with Pt-like activity,” Adv.
Energy Mater. 9(5), 1803369 (2018). https://doi.org/10.1002/aenm.201803369 1 M
KOH 28 28.7 Ru@NG-2 1 M H2SO4 0.857 74 48 5000 CV or −100 mV @ 10 h 129129. B.
K. Barman, D. Das, and K. K. Nanda, “ Facile synthesis of ultrafine Ru
nanocrystal supported N-doped graphene as an exceptional hydrogen evolution
electrocatalyst in both alkaline and acidic media,” Sustainable Energy Fuels
1(5), 1028–1033 (2017). https://doi.org/10.1039/C7SE00153C 1 M KOH 47 82 Ir NWs
0.05 M H2SO4 40.7 μgIr cm−2 17 26 … 136136. J. Yang, Y. Ji, Q. Shao, N. Zhang,
Y. Li, and X. Huang, “ A universal strategy to metal wavy nanowires for
efficient electrochemical water splitting at pH-universal conditions,” Adv.
Funct. Mater. 28(41), 1803722 (2018). https://doi.org/10.1002/adfm.201803722 0.5
M H2SO4 15 34 … 0.1 M KOH 73 46 … 1 M KOH 38 30 … RhCo–ANAs 0.5 M H2SO4 2 12.4
30.7 … 1111. Y. Zhao, J. Bai, X.-R. Wu, P. Chen, P.-J. Jin, H.-C. Yao, and Y.
Chen, “ Atomically ultrathin RhCo alloy nanosheet aggregates for efficient water
electrolysis in broad pH range,” J. Mater. Chem. A 7(27), 16437–16446 (2019).
https://doi.org/10.1039/C9TA05334D 1 M PBS 31 33.6 −50 mV @ 5 h 1 M KOH 32.4
31.9 … Monodisperse Rh2P NPs 0.5 M H2SO4 0.0306 14 31.7 1000 CV 8585. F. Yang,
Y. Zhao, Y. Du, Y. Chen, G. Cheng, S. Chen, and W. Luo, “ A monodisperse
Rh2P-based electrocatalyst for highly efficient and pH-universal hydrogen
evolution reaction,” Adv. Energy Mater. 8(18), 1703489 (2018).
https://doi.org/10.1002/aenm.201703489 1 M PBS 38 46 1 M KOH 30 50 Pd@PtCu
dodecahedron 0.5 M H2SO4 15 μgPt cm−2 19 26.2 10 000 CV 163163. M. Bao, I. S.
Amiinu, T. Peng, W. Li, S. Liu, Z. Wang, Z. Pu, D. He, Y. Xiong, and S. Mu, “
Surface evolution of PtCu alloy shell over Pd nanocrystals leads to superior
hydrogen evolution and oxygen reduction reactions,” ACS Energy Lett. 3(4),
940–945 (2018). https://doi.org/10.1021/acsenergylett.8b00330 0.1 M KOH 60 …
Ru-MoS2/CC 0.5 M H2SO4 46 μgRu cm−2 61 … −10 mA cm−2 @ 20 h 195195. D. Wang, Q.
Li, C. Han, Z. Xing, and X. Yang, “ Single-atom ruthenium based catalyst for
enhanced hydrogen evolution,” Appl. Catal. B 249(15), 91–97 (2019).
https://doi.org/10.1016/j.apcatb.2019.02.059 1 M PBS 114 … −10 mA cm−2 @ 10 h 1
M KOH 41 114 −10 mA cm−2 @ 10 h NiCo2S4/Pd 0.5 M H2SO4 0.306 87 70 −10 mA cm−2 @
10 h 197197. G. Sheng, J. Chen, Y. Li, H. Ye, Z. Hu, X.-Z. Fu, R. Sun, W. Huang,
and C.-P. Wong, “ Flowerlike NiCo2S4 hollow sub-microspheres with mesoporous
nanoshells support Pd nanoparticles for enhanced hydrogen evolution reaction
electrocatalysis in both acidic and alkaline conditions,” ACS Appl. Mater.
Interfaces 10(26), 22248–22256 (2018). https://doi.org/10.1021/acsami.8b05427 1
M KOH 83 123 Ir_VG 0.5 M H2SO4 50 μgIr cm−2 47 43 1000 CV 221221. S. B. Roy, K.
Akbar, J. H. Jeon, S.-K. Jerng, L. Truong, K. Kim, Y. Yi, and S.-H. Chun, “
Iridium on vertical graphene as an all-round catalyst for robust water splitting
reactions,” J. Mater. Chem. A 7(36), 20590–20596 (2019).
https://doi.org/10.1039/C9TA07388D 1 M KOH 17 29 Rh NP/PC 1 M KOH 0.6 33 … 1000
CV 128128. M. Ming, Y. Zhang, C. He, L. Zhao, S. Niu, G. Fan, and J. S. Hu, “
Room-temperature sustainable synthesis of selected platinum group metal
(PGM = Ir, Rh, and Ru) nanocatalysts well-dispersed on porous carbon for
efficient hydrogen evolution and oxidation,” Small 15(49), 1903057 (2019).
https://doi.org/10.1002/smll.201903057 0.5 M H2SO4 21 34 Ru NP/PC 1 M KOH 30 …
0.5 M H2SO4 63 63 Ir NP/PC 1 M KOH 110 … 0.5 M H2SO4 30 35 Ru@SC-CQDs 0.5 M
H2SO4 0.42 59 57 5000 CV or Initial −10 mA cm−2 @ 100 h 229229. Y. Liu, Y. Yang,
Z. Peng, Z. Liu, Z. Chen, L. Shang, S. Lu, and T. Zhang, “ Self-crosslinking
carbon dots loaded ruthenium dots as an efficient and super-stable hydrogen
production electrocatalyst at all pH values,” Nano Energy 65, 104023 (2019).
https://doi.org/10.1016/j.nanoen.2019.104023 1 M PBS 66 158 1 M KOH 29 57
RuNi-NCNFs 0.5 M H2SO4 0.612 23 29 5500 CV or −62 mV @ 12 h 228228. M. Li, H.
Wang, W. Zhu, W. Li, C. Wang, and X. Lu, “ RuNi nanoparticles embedded in
N-doped carbon nanofibers as a robust bifunctional catalyst for efficient
overall water splitting,” Adv. Sci. 7(2), 1901833 (2020).
https://doi.org/10.1002/advs.201901833 1 M KOH 35 30 6000 CV or −40 mV @ 12 h
Pd-CNx 0.5 M H2SO4 43 μgPd cm−2 55 35 10 000 CV or −60 mV @ 100 h 230230. T.
Bhowmik, M. K. Kundu, and S. Barman, “ Palladium nanoparticle-graphitic carbon
nitride porous synergistic catalyst for hydrogen evolution/oxidation reactions
over a broad range of pH and correlation of its catalytic activity with measured
hydrogen binding energy,” ACS Catal. 6(3), 1929–1941 (2016).
https://doi.org/10.1021/acscatal.5b02485 0.5 M KOH 180 (η5) 150 … Ir@CON 0.5 M
H2SO4 0.5 13.6 27 10 000 CV 219219. J. Mahmood, M. A. R. Anjum, S. H. Shin, I.
Ahmad, H. J. Noh, S. J. Kim, H. Y. Jeong, J. S. Lee, and J. B. Baek, “
Encapsulating iridium nanoparticles inside a 3D cage-like organic network as an
efficient and durable catalyst for the hydrogen evolution reaction,” Adv. Mater.
30(52), 1805606 (2018). https://doi.org/10.1002/adma.201805606 1 M KOH 13.5 29
RuSA-N-S-Ti3C2Tx 0.5 M H2SO4 1 76 90 3000 CV 263263. V. Ramalingam, P. Varadhan,
H. C. Fu, H. Kim, D. Zhang, S. Chen, L. Song, D. Ma, Y. Wang, and H. N.
Alshareef, “ Heteroatom‐mediated interactions between ruthenium single atoms and
an MXene support for efficient hydrogen evolution,” Adv. Mater. 31(48), 1903841
(2019). https://doi.org/10.1002/adma.201903841 0.5 M Na2SO4 275 … 1000 CV 0.5 M
NaOH 99 … 4000 CV
B. Bifunctional water electrolysis
For the sake of cost-effective overall water splitting, the other aim is to
construct active bifunctional electrocatalysts that could effectively catalyze
the OER and HER at the same time. Based on numerous pioneering studies, non-Pt
NMNs not only possess the pronounced HER catalytic performance in the pH range
of 0–14, but also are considered as the most promising pH-universal OER
catalysts, typically Ru or Ir-based materials, due to the moderate binding
energy of the O-related reaction intermediates and great acid–base
durability.3333. Q. Shi, C. Zhu, D. Du, and Y. Lin, “ Robust noble metal-based
electrocatalysts for oxygen evolution reaction,” Chem. Soc. Rev. 48(12),
3181–3192 (2019). https://doi.org/10.1039/C8CS00671G It is worth mentioning that
pure Ru or Ir-based oxides or metals, especially Ru metal, are relatively
unstable due to the dissolution from the excessive oxidation during the OER
process, but various design tactics, such as forming alloys, optimizing
morphology, constructing hybrids, tuning crystalline structures or facets, etc.,
greatly propel their OER stability.1212. J. Yu, Q. He, G. Yang, W. Zhou, Z.
Shao, and M. Ni, “ Recent advances and prospective in ruthenium-based materials
for electrochemical water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b02457 Our previous review has given an
important focus on this stability issue.1212. J. Yu, Q. He, G. Yang, W. Zhou, Z.
Shao, and M. Ni, “ Recent advances and prospective in ruthenium-based materials
for electrochemical water splitting,” ACS Catal. 9(11), 9973–10011 (2019).
https://doi.org/10.1021/acscatal.9b02457 Here, overall, this “bifunctionality”
concept can be accomplished by developing these novel non-Pt NMNs. For instance,
an Ir/controllable IrOx stabilized by Cucurbit[6]uril (CB[6]) worked as a
distinguished bifunctional electrocatalyst for acidic water splitting
(CB[6]-Ir2).264264. H. You, D. Wu, Z.-N. Chen, F. Sun, H. Zhang, Z. Chen, M.
Cao, W. Zhuang, and R. Cao, “ Highly active and stable water splitting in acidic
media using a bifunctional iridium/cucurbit, [6] uril catalyst,” ACS Energy
Lett. 4(6), 1301–1307 (2019). https://doi.org/10.1021/acsenergylett.9b00553 The
overall water-splitting voltage was only 1.56 V at the 10 mA cm−2 current
density and the activity at 5 mA cm−2 could be continuously maintained for at
least 20 h, which strikingly went beyond the benchmark for Pt/C–Ir/C. In
accordance to spectroscopic measurements and DFT calculations, the strong
coordination bonding between surface Ir and CB[6] controllably created the
surface-active IrOx species and promoted their stabilization, which contributed
to the superb activity and stability as observed. Lai et al. explored a novel
composite of various single-atom sites (M1= Fe1, Ni1, Ru1, Pd1, Pt1, and Ir1)
anchored on the ZIF-67-derived Co/NC substrate (namely M1@Co/NC), which featured
two different active domains, that is M1@Co and M1@NC, being responsible for the
OER and HER in basic solution, respectively.265265. W. H. Lai, L. F. Zhang, W.
B. Hua, S. Indris, Z. C. Yan, Z. Hu, B. Zhang, Y. Liu, L. Wang, and M. Liu, “
General π-electron-assisted strategy for Ir, Pt, Ru, Pd, Fe, Ni single-atom
electrocatalysts with bifunctional active sites for highly efficient water
splitting,” Angew. Chem., Int. Ed. 131(34), 11994–11999 (2019).
https://doi.org/10.1002/ange.201904614 To be noted, the Ir1@Co/NC was the best
one for the overall water splitting, showing a 1.603 V cell potential at 10 mA
cm−2. Reported by Huang's group, channel-rich RuCu nanosheets (NSs) that
crystallized Ru integrated with amorphous Cu were also proven as active and
robust electrocatalysts for the OER and HER at a wide range of pH values.145145.
Q. Yao, B. Huang, N. Zhang, M. Sun, Q. Shao, and X. Huang, “ Channel-rich RuCu
nanosheets for pH-universal overall water splitting electrocatalysis,” Angew.
Chem., Int. Ed. 58(39), 13983–13988 (2019).
https://doi.org/10.1002/anie.201908092 By controlling the synthesis temperature,
the RuCu nanosheets as the optimal OER and HER catalysts were achieved at 350
and 250 °C, respectively. The assembly of two electrodes with the optimized RuCu
material as the cathode and anode offered an attractive electrocatalytic system
with cell voltages of only 1.50, 1.49, 1.55, and 1.49 V in 0.05 M H2SO4, 0.5 M
H2SO4, 0.1 M KOH, and 1 M KOH solutions, respectively, and high stability over
30 h, which were the highest performance results among those reported
electrocatalysts used for water electrolysis and much better than the results of
Pt/C–Ir/C. Additionally, in the fourth part, the bifunctional water electrolysis
was well reflected by some representative cases, like IrNi NCs, IrW ND, RuIrOx,
Li-IrSe2, NiVIr LDH, Ir_VG, etc.50,62,69,99,115,22150. Y. Pi, Q. Shao, P. Wang,
J. Guo, and X. Huang, “ General formation of monodisperse IrM (M = Ni, Co, Fe)
bimetallic nanoclusters as bifunctional electrocatalysts for acidic overall
water splitting,” Adv. Funct. Mater. 27(27), 1700886 (2017).
https://doi.org/10.1002/adfm.20170088662. F. Lv, J. Feng, K. Wang, Z. Dou, W.
Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “ Iridium-tungsten alloy
nanodendrites as pH-universal water-splitting electrocatalysts,” ACS Cent. Sci.
4(9), 1244–1252 (2018). https://doi.org/10.1021/acscentsci.8b0042669. Z. Zhuang,
Y. Wang, C.-Q. Xu, S. Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S.
Lu, “ Three-dimensional open nano-netcage electrocatalysts for efficient
pH-universal overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-099. T. Zheng, C. Shang, Z. He, X.
Wang, C. Cao, H. Li, R. Si, B. Pan, S. Zhou, and J. Zeng, “ Intercalated iridium
diselenide electrocatalysts for efficient pH-universal water splitting,” Angew.
Chem., Int. Ed. 131(41), 14906–14911 (2019).
https://doi.org/10.1002/ange.201909369115. S. Li, C. Xi, Y.-Z. Jin, D. Wu, J.-Q.
Wang, T. Liu, H.-B. Wang, C.-K. Dong, H. Liu, and S. A. Kulinich, “ Ir-O-V
catalytic group in Ir-doped NiV(OH)2 for overall water splitting,” ACS Energy
Lett. 4(8), 1823–1829 (2019). https://doi.org/10.1021/acsenergylett.9b01252221.
S. B. Roy, K. Akbar, J. H. Jeon, S.-K. Jerng, L. Truong, K. Kim, Y. Yi, and
S.-H. Chun, “ Iridium on vertical graphene as an all-round catalyst for robust
water splitting reactions,” J. Mater. Chem. A 7(36), 20590–20596 (2019).
https://doi.org/10.1039/C9TA07388D Table V lists the overall water-splitting
performance of various non-Pt NMN catalysts under different operation
conditions. Of note, most of them are also obviously superior to those of other
representative bifunctional electrocatalysts for overall water splitting, as
summarized in Table VI.
TABLE V. Summary of various non-Pt NMN catalysts toward overall water splitting
in different media.
Catalyst Electrolyte η10 (mV) Cell voltage (V) at 10 mA cm−2 Stability Loading
(mg cm−2) References Ir6Ag9 NTs 0.5 M H2SO4 OER 285 1.55 1000 CV or 5 mA cm−2 @
32 h 13.3 μgIr cm−2 3434. M. Zhu, Q. Shao, Y. Qian, and X. Huang, “ Superior
overall water splitting electrocatalysis in acidic conditions enabled by
bimetallic Ir-Ag nanotubes,” Nano Energy 56, 330–337 (2019).
https://doi.org/10.1016/j.nanoen.2018.11.023 HER 20 IrNi NCs 0.5 M H2SO4 OER
>300 1.58 1.6 V @ 10 h 12.5 μgIr cm−2 5050. Y. Pi, Q. Shao, P. Wang, J. Guo, and
X. Huang, “ General formation of monodisperse IrM (M = Ni, Co, Fe) bimetallic
nanoclusters as bifunctional electrocatalysts for acidic overall water
splitting,” Adv. Funct. Mater. 27(27), 1700886 (2017).
https://doi.org/10.1002/adfm.201700886 HER >20 IrNi NFs 0.5 M H2SO4 OER 330 1.6
1000 CV 30 μgIr cm−2 5151. F. Lv, W. Zhang, W. Yang, J. Feng, K. Wang, J. Zhou,
P. Zhou, and S. Guo, “ Ir-based alloy nanoflowers with optimized hydrogen
binding energy as bifunctional electrocatalysts for overall water splitting,”
Small Methods 4(6), 1900129 (2020). https://doi.org/10.1002/smtd.201900129 HER
40 IrW ND 0.5 M H2SO4 … 1.48 10 mA cm−2 @ 8 h 30 μgIr cm−2 6262. F. Lv, J. Feng,
K. Wang, Z. Dou, W. Zhang, J. Zhou, C. Yang, M. Luo, Y. Yang, and Y. Li, “
Iridium-tungsten alloy nanodendrites as pH-universal water-splitting
electrocatalysts,” ACS Cent. Sci. 4(9), 1244–1252 (2018).
https://doi.org/10.1021/acscentsci.8b00426 1M PBS … 1.55 (onset) … 1 M KOH …
1.50 (onset) … Co-RuIr 0.1 M HClO4 OER 235 1.52 10 mA cm−2 @ 25 h … 6767. J.
Shan, T. Ling, K. Davey, Y. Zheng, and S. Z. Qiao, “ Transition-metal-doped RuIr
bifunctional nanocrystals for overall water splitting in acidic environments,”
Adv. Mater. 31(17), 1900510 (2019). https://doi.org/10.1002/adma.201900510 HER
14 RuIrOx 0.5 M H2SO4 OER 233 1.45 Initial 10 mA cm−2 @ 20 h 1 6969. Z. Zhuang,
Y. Wang, C.-Q. Xu, S. Liu, C. Chen, Q. Peng, Z. Zhuang, H. Xiao, Y. Pan, and S.
Lu, “ Three-dimensional open nano-netcage electrocatalysts for efficient
pH-universal overall water splitting,” Nat. Commun. 10, 4875 (2019).
https://doi.org/10.1038/s41467-019-12885-0 HER 12 PBS (pH = 3/7/9) …
1.52/1.51/1.53 1 M KOH OER 250 1.47 HER 13 PdP2@CB 1 M PBS OER 277 1.59 Initial
10/50 mA cm−2 @ 10 h 0.285 9292. F. Luo, Q. Zhang, X. Yu, S. Xiao, Y. Ling, H.
Hu, L. Guo, Z. Yang, L. Huang, and W. Cai, “ Palladium phosphide as a stable and
efficient electrocatalyst for overall water splitting,” Angew. Chem., Int. Ed.
57(45), 14862–14867 (2018). https://doi.org/10.1002/anie.201810102 HER 84.6 1 M
KOH OER 270 1.72 (at 50 mA cm−2) HER 35.4 RuS2-500 1 M KOH OER 282 1.527 10 mA
cm−2 @ 20 h 1.5 100100. Y. Zhu, H. A. Tahini, Y. Wang, Q. Lin, Y. Liang, C. M.
Doherty, Y. Liu, X. Li, J. Lu, and S. C. Smith, “ Pyrite-type ruthenium
disulfide with tunable disorder and defects enables ultra-efficient overall
water splitting,” J. Mater. Chem. A 7(23), 14222–14232 (2019).
https://doi.org/10.1039/C9TA04120F HER 78 Li-IrSe2 0.5 M H2SO4 OER 220 1.44 1.47
V @ 24 h 1.57 V @ 24 h 1.52 V @ 24 h 3 9999. T. Zheng, C. Shang, Z. He, X. Wang,
C. Cao, H. Li, R. Si, B. Pan, S. Zhou, and J. Zeng, “ Intercalated iridium
diselenide electrocatalysts for efficient pH-universal water splitting,” Angew.
Chem., Int. Ed. 131(41), 14906–14911 (2019).
https://doi.org/10.1002/ange.201909369 HER 55 1 M PBS OER 315 1.50 HER 120 1 M
KOH OER 270 1.48 HER 72 NiFeRu–LDH 1 M KOH OER 225 1.52 10 mA cm−2 @ 10 h 1.2
117117. G. Chen, T. Wang, J. Zhang, P. Liu, H. Sun, X. Zhuang, M. Chen, and X.
Feng, “ Accelerated hydrogen evolution kinetics on NiFe-layered double hydroxide
electrocatalysts by tailoring water dissociation active sites,” Adv. Mater.
30(10), 1706279 (2018). https://doi.org/10.1002/adma.201706279 HER 29
Rh–NiFe–LDH 1 M KOH OER 206 1.46 1.5 V @ 2.78 h 1.2 1818. B. Zhang, C. Zhu, Z.
Wu, E. Stavitski, Y. H. Lui, T.-H. Kim, H. Liu, L. Huang, X. Luan, and L. Zhou,
“ Integrating Rh species with NiFe-layered double hydroxide for overall water
splitting,” Nano Lett. 20(1), 136–144 (2020).
https://doi.org/10.1021/acs.nanolett.9b03460 HER 57 NiVIr LDH 1 M KOH OER 203
1.49 10 mA cm−2 @ >15 h 1.7 115115. S. Li, C. Xi, Y.-Z. Jin, D. Wu, J.-Q. Wang,
T. Liu, H.-B. Wang, C.-K. Dong, H. Liu, and S. A. Kulinich, “ Ir-O-V catalytic
group in Ir-doped NiV(OH)2 for overall water splitting,” ACS Energy Lett. 4(8),
1823–1829 (2019). https://doi.org/10.1021/acsenergylett.9b01252 HER 41 Ru–NiFe–P
1 M KOH OER 242 (η100) 1.47 ∼1.47 V @ 20 h … 119119. M. Qu, Y. Jiang, M. Yang,
S. Liu, Q. Guo, W. Shen, M. Li, and R. He, “ Regulating electron density of
NiFe-P nanosheets electrocatalysts by a trifle of Ru for high-efficient overall
water splitting,” Appl. Catal. B 263, 118324 (2020).
https://doi.org/10.1016/j.apcatb.2019.118324 HER 44 RhCo–ANAs 0.5 M H2SO4 OER
>220 1.51 … 2 1111. Y. Zhao, J. Bai, X.-R. Wu, P. Chen, P.-J. Jin, H.-C. Yao,
and Y. Chen, “ Atomically ultrathin RhCo alloy nanosheet aggregates for
efficient water electrolysis in broad pH range,” J. Mater. Chem. A 7(27),
16437–16446 (2019). https://doi.org/10.1039/C9TA05334D HER 12.4 1 M PBS OER 310
1.54 1.54 V @ 20 h HER 31 1 M KOH OER >220 1.47 … HER 32.4 Ir/MoS2 1 M KOH OER
330 1.57 … … 190190. S. Wei, X. Cui, Y. Xu, B. Shang, Q. Zhang, L. Gu, X. Fan,
L. Zheng, C. Hou, and H. Huang, “ Iridium-triggered phase transition of MoS2
nanosheets boosts overall water splitting in alkaline media,” ACS Energy Lett.
4(1), 368–374 (2019). https://doi.org/10.1021/acsenergylett.8b01840 HER 44
Co(OH)2–Au–Ni(OH)2 1 M NaOH OER 340 1.75 10 mA cm−2 @ 0.5 h … 201201. U. K.
Sultana, J. D. Riches, and A. P. O'Mullane, “ Gold doping in a layered Co-Ni
hydroxide system via galvanic replacement for overall electrochemical water
splitting,” Adv. Funct. Mater. 28(43), 1804361 (2018).
https://doi.org/10.1002/adfm.201804361 HER 200 Ir_VG 0.5 M H2SO4 OER 300 1.58 …
50 μgIr cm−2 221221. S. B. Roy, K. Akbar, J. H. Jeon, S.-K. Jerng, L. Truong, K.
Kim, Y. Yi, and S.-H. Chun, “ Iridium on vertical graphene as an all-round
catalyst for robust water splitting reactions,” J. Mater. Chem. A 7(36),
20590–20596 (2019). https://doi.org/10.1039/C9TA07388D HER 47 1 M KOH OER 320
1.57 … HER 17 RuNi–NCNFs 1 M KOH OER 290 1.564 1.57 V @ 0.5 h 2.5 228228. M. Li,
H. Wang, W. Zhu, W. Li, C. Wang, and X. Lu, “ RuNi nanoparticles embedded in
N-doped carbon nanofibers as a robust bifunctional catalyst for efficient
overall water splitting,” Adv. Sci. 7(2), 1901833 (2020).
https://doi.org/10.1002/advs.201901833 HER 35 CB[6]-Ir2 0.5 M H2SO4 OER 270 1.56
5 mA cm−2 @ 20 h … 264264. H. You, D. Wu, Z.-N. Chen, F. Sun, H. Zhang, Z. Chen,
M. Cao, W. Zhuang, and R. Cao, “ Highly active and stable water splitting in
acidic media using a bifunctional iridium/cucurbit, [6] uril catalyst,” ACS
Energy Lett. 4(6), 1301–1307 (2019).
https://doi.org/10.1021/acsenergylett.9b00553 HER 50–60 Ir1@Co/NC 1 M KOH OER
260 1.603 1.61 V @ 5 h 0.2 265265. W. H. Lai, L. F. Zhang, W. B. Hua, S. Indris,
Z. C. Yan, Z. Hu, B. Zhang, Y. Liu, L. Wang, and M. Liu, “ General
π-electron-assisted strategy for Ir, Pt, Ru, Pd, Fe, Ni single-atom
electrocatalysts with bifunctional active sites for highly efficient water
splitting,” Angew. Chem., Int. Ed. 131(34), 11994–11999 (2019).
https://doi.org/10.1002/ange.201904614 HER 60 RuCu NSs 0.05 M H2SO4 OER 240 1.50
… 145145. Q. Yao, B. Huang, N. Zhang, M. Sun, Q. Shao, and X. Huang, “
Channel-rich RuCu nanosheets for pH-universal overall water splitting
electrocatalysis,” Angew. Chem., Int. Ed. 58(39), 13983–13988 (2019).
https://doi.org/10.1002/anie.201908092 HER 27 0.5 M H2SO4 OER 236 1.49 10 mA
cm−2 @ 15 h HER 19 0.1 M KOH OER 276 1.55 HER 40 1 M KOH OER 234 1.49 10 mA cm−2
@ 30 h HER 20
TABLE VI. Summary of various other representative bifunctional electrocatalysts
toward overall water splitting in different media.
Catalyst Electrolyte η10 (mV) Cell voltage (V) at 10 mA cm−2 Stability Loading
(mg cm−2) References SrNb0.1Co0.7Fe0.2O3-δ nanorods (SNCF-NRs) 1 M KOH OER 370
1.68 10 mA cm−2 @ 30 h 3 266266. Y. Zhu, W. Zhou, Y. Zhong, Y. Bu, X. Chen, Q.
Zhong, M. Liu, and Z. Shao, “ A perovskite nanorod as bifunctional
electrocatalyst for overall water splitting,” Adv. Energy Mater. 7(8), 1602122
(2017). https://doi.org/10.1002/aenm.201602122 HER 232 CoP@a-CoOx plate/C 1 M
KOH OER 232 1.66 10 mA cm−2 @ 30 h 5 261261. J. Yu, Y. Zhong, X. Wu, J. Sunarso,
M. Ni, W. Zhou, and Z. Shao, “ Bifunctionality from synergy: CoP nanoparticles
embedded in amorphous CoOx nanoplates with heterostructures for highly efficient
water electrolysis,” Adv. Sci. 5(9), 1800514 (2018).
https://doi.org/10.1002/advs.201800514 HER 132 N-WC 0.5 M H2SO4 OER ∼220 <1.7
(at 30 mA cm−2) … 5 267267. N. Han, K. R. Yang, Z. Lu, Y. Li, W. Xu, T. Gao, Z.
Cai, Y. Zhang, V. S. Batista, W. Liu, and X. Sun, “ Nitrogen-doped tungsten
carbide nanoarray as an efficient bifunctional electrocatalyst for water
splitting in acid,” Nat. Commun. 9, 924 (2018).
https://doi.org/10.1038/s41467-018-03429-z HER 113 NC-CNT/CoP 0.5 M H2SO4 OER
350 1.66 1.7 V @ 20 h 1.5 268268. C. Guan, H. Wu, W. Ren, C. Yang, X. Liu, X.
Ouyang, Z. Song, Y. Zhang, S. J. Pennycook, C. Cheng, and J. Wang, “
Metal–organic framework-derived integrated nanoarrays for overall water
splitting,” J. Mater. Chem. A 6, 9009–9018 (2018).
https://doi.org/10.1039/C8TA02528B HER 62 1M PBS OER 420 1.69 1.75 V @ 20 h HER
45 1 M KOH OER 240 1.63 1.75 V @ 20 h HER 120 single-walled carbon nanotubes
(SWCNTs)/MoSe2-2:Mo2C 0.5 M H2SO4 OER 197 … … … 269269. L. Najafi, S. Bellani,
R. Oropesa-Nunez, M. Prato, B. Martín-García, R. Brescia, and F. Bonaccorso, “
Carbon nanotube-supported MoSe2 holey flake: Mo2C ball hybrids for bifunctional
pH-universal water splitting,” ACS Nano 13(3), 3162–3176 (2019).
https://doi.org/10.1021/acsnano.8b08670 HER 49 1 M KOH OER 241 HER 89
NiCo-nitrides/NiCo2O4/GF 0.5 M H2SO4 OER 460 1.57 1.4 V @ 40 h … 270270. Z. Liu,
H. Tan, D. Liu, X. Liu, J. Xin, J. Xie, M. Zhao, L. Song, L. Dai, and H. Liu, “
Promotion of overall water splitting activity over a wide pH range by
interfacial electrical effects of metallic NiCo-nitrides nanoparticle/NiCo2O4
nanoflake/graphite fibers,” Adv. Sci. 6(5), 1801829 (2019).
https://doi.org/10.1002/advs.201801829 HER 432 1 M PBS OER 673 … HER 418 1 M KOH
OER 183 … HER 71 Co/CoP-5 0.5 M H2SO4 OER … 1.89 (at 1 mA cm−2) 20 mA cm−2 @ 12
h 5 271271. Z.-H. Xue, H. Su, Q.-Y. Yu, B. Zhang, H.-H. Wang, X.-H. Li, and
J.-S. Chen, “ Janus Co/CoP nanoparticles as efficient Mott–Schottky
electrocatalysts for overall water splitting in wide pH range,” Adv. Energy
Mater. 7(12), 1602355 (2017). https://doi.org/10.1002/aenm.201602355 HER 178 1 M
PBS OER … 1.51 10 mA cm−2 @ 12 h HER 138 1 M KOH OER 340 1.45 1 mA cm−2 @ 12 h
HER 253 Mo-Co9S8@C 0.5 M H2SO4 OER 370 1.68 1.65 V @ 24 h … 1.65 V @ 24 h 1
272272. L. Wang, X. Duan, X. Liu, J. Gu, R. Si, Y. Qiu, Y. Qiu, D. Shi, F. Chen,
X. Sun, J. Lin, and J. Sun, “ Atomically dispersed Mo supported on metallic
Co9S8 nanoflakes as an advanced noble-metal-free bifunctional water splitting
catalyst working in universal pH conditions,” Adv. Energy Mater. 10(4), 1903137
(2020). https://doi.org/10.1002/aenm.201903137 HER 98 0.5 M Na2SO4 OER 290 (η0)
… HER 140 1 M KOH OER 200 1.56 HER 113 MoSe2 NS/MoO2 nanobelt (NB)/CNT-M 0.5 M
H2SO4 OER 162 (η20) 1.63 2 V @ 10 h … 273273. L. J. Yang, Y. Q. Deng, X. F.
Zhang, H. Liu, and W. J. Zhou, “ MoSe2 nanosheet/MoO2 nanobelt/carbon nanotube
membrane as flexible and multifunctional electrodes for full water splitting in
acidic electrolyte,” Nanoscale 10, 9268–9275 (2018).
https://doi.org/10.1039/C8NR01572D HER 97 S-NiFe2O4/nickel foam (NF) 1 M PBS OER
494 1.95 1.95 V @ 24 h … 274274. J. Liu, D. Zhu, T. Ling, A. Vasileff, and S.-Z.
Qiao, “ S-NiFe2O4 ultra-small nanoparticle built nanosheets for efficient water
splitting in alkaline and neutral pH,” Nano Energy 40, 264–273 (2017).
https://doi.org/10.1016/j.nanoen.2017.08.031 HER 197 CoO/Co4N 1 M PBS OER 398
1.79 10 mA cm−2 @ 50 h 3.8 275275. R.-Q. Li, P. Hu, M. Miao, Y. Li, X.-F. Jiang,
Q. Wu, Z. Meng, Z. Hu, Y. Bando, and X.-B. Wang, “ CoO-modified Co4N as a
heterostructured electrocatalyst for highly efficient overall water splitting in
neutral media,” J. Mater. Chem. A 6, 24767–24772 (2018).
https://doi.org/10.1039/C8TA08519F HER 145
NiCo2Te4/perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) 1 M PBS OER 120
1.55 1.61 V @ 30 h … 276276. L. Tao, M. Huang, S. Guo, Q. Wang, M. Lia, X. Xiao,
G. Cao, Y. Shao, Y. Shen, Y. Fu, and M. Wang, “ Surface modification of NiCo2Te4
nanoclusters: A highly efficient electrocatalyst for overall water-splitting in
neutral solution,” Appl. Catal. B 254(5), 424–431 (2019).
https://doi.org/10.1016/j.apcatb.2019.05.010 HER 60 p-FGDY/CC 0.5 M H2SO4 OER
570 1.80 … … 277277. C. Xing, Y. Xue, B. Huang, H. Yu, L. Hui, Y. Fang, Y. Liu,
Y. Zhao, Z. Li, and Y. Li, “ Fluorographdiyne: A metal-free catalyst for
applications in water reduction and oxidation,” Angew. Chem., Int. Ed. 131(39),
14035–14041 (2019). https://doi.org/10.1002/ange.201905729 HER 92 1 M PBS OER
623 … … HER … 1 M KOH OER 460 1.75 1.76 V @ 7 h HER 82 CoMoNiS-NF-31 0.5 M H2SO4
OER 228 1.45 1.53 V @ 20 h 1.86 278278. Y. Yang, H. Yao, Z. Yu, S. M. Islam, H.
He, M. Yuan, Y. Yue, K. Xu, W. Hao, G. Sun, H. Li, S. Ma, P. Zapol, and M. G.
Kanatzidis, “ Hierarchical nanoassembly of MoS2/Co9S8/Ni3S2/Ni as a highly
efficient electrocatalyst for overall water splitting in a wide pH range,” J.
Am. Chem. Soc. 141(26), 10417–10430 (2019). https://doi.org/10.1021/jacs.9b04492
HER 103 1 M PBS OER 405 1. 80 1.80 V @ 20 h HER 117 1 M KOH OER 166 1.54 1.70 V
@ 20 h HER 113 Cu-CoP nanosheet arrays (NAs)/CP 1 M PBS OER 411 1.72 10 mA cm−2
@ 60 h 279279. L. Yan, B. Zhang, J. Zhu, Y. Li, P. Tsiakaras, and P. K. Shen, “
Electronic modulation of cobalt phosphide nanosheet arrays via copper doping for
highly efficient neutral-pH overall water splitting,” Appl. Catal. B 265(15),
118555 (2020). https://doi.org/10.1016/j.apcatb.2019.118555 HER 81
VI. CONCLUSIONS AND OUTLOOK
Section:
ChooseTop of pageABSTRACTI. INTRODUCTIONII. FUNDAMENTALS OF THE H...III. BRIEF
OVERVIEW OF TH...IV. CONSTRUCTING ROBUST N...V. NEW TRENDS IN THE ELEC...VI.
CONCLUSIONS AND OUTLO... <<Choose
Over the past few years, considerable breakthroughs have been continuously
attained for the construction of non-Pt noble metal-based nanomaterials toward
more prominent hydrogen-evolution behavior. In this comprehensive review, we
summarize the recent progresses of them, particularly over the past five years.
These non-Pt noble metals, with suitable hydrogen-adsorption energy and robust
corrosion resistance, afforded splendid catalytic performance over a wide pH
range. Through the rational compositional and structural tailoring: (i) creating
alloys (noble metal–noble metal or noble metal–transition metal), (ii)
constructing novel metal compounds, such as oxides, phosphides, chalcogenides,
carbides, etc., (iii) decreasing the particle size to a few nanometers or
designing unique nanostructures, i.e., 1D, 2D, and 3D shapes, (iv) coupling with
carbon-free active materials or supporting with conductive substrates, and (v)
adjusting crystalline structures or exposed facets, the number of active sites,
the electron conductivity, and the reaction kinetics could be remarkably
ameliorated, correspondingly leading to the considerable improvement in
electrocatalytic performances, in accompaniment with reducing the dosage of
noble metals. Some representative non-Pt NMN electrocatalysts are listed in
Tables I–III. Moreover, the development of non-Pt NMNs highly follows the
desired trends in the electrocatalytic HER (Tables IV and V), that is, they
could work well in pH-universal electrolytes and simultaneously catalyze the OER
and HER under the same conditions, which are crucial for large-scale
applications.
Despite these enormous promising advances, there always exists a lot of
insufficient understanding, accompanied by the booming development. For this
attractive field, there is still a long way to go. Many significant points are
profiled below, some of which are not only suited to non-Pt NMN catalysts, but
also beneficial to the development of other electrocatalysts.
First, currently, in order to acquire various effective non-Pt NMN HER
electrocatalysts with a low concentration of noble metal, multifarious synthetic
tactics have been widely adopted. However, it should be noted that most of these
synthesis routes are much complicated with high energy-consumption, which leads
to the high production cost of catalysts as well as sometimes offers poor
quality and yield of the final products. All of these are very hard to meet the
requirement for commercialization. Therefore, it is of great significance to
develop gentle and simple methods for large-scale synthesis of the admirable
catalysts with less precious metal.
Second, albeit predecessors have designed a great deal of non-Pt NMNs with
different nanostructures, constructing non-Pt NMNs with several novel
morphologies still faces a huge challenge. Limited porous morphologies,
especially for nanosheets, hindered the excavation and exploitation of more
superior and robust HER electrocatalysts. As is generally agreed, structuring
hierarchical porous catalysts can provide rich accessible pores, a large
inventory of defects, and large surface areas, which is in favor of the active
site exposure, charge transfer, and mass diffusion. Hydrogen evolution is a
surface-dependent and gas-involving process, in which the amounts of active
sites and the ability of electron/mass transfer for a catalytic material highly
affect the resulting catalytic performance. Accordingly, it is highly desirable
to explore porous-structured non-Pt NMN electrocatalysts via reasonable and
effective pathways, such as templating or self-corrosion methods.
Third, to precisely probe the catalytic activity and exhaustively understand the
electronic structure–property relationship in these outstanding catalytic
materials, some in situ spectroscopic techniques, like in situ Raman, XRD, XAS,
etc., are highly desirable in widespread use. Besides, DFT calculation is
regarded as a powerful tool to simulate the HER electrocatalytic process
occurring on the surface of the catalytic material at the molecular scale.
Specifically, it can predict the energy barrier of water dissociation and
adsorption/desorption energies of hydrogen intermediates, so as to distinguish
the active sites and reveal the possible rate-determining step. Of note, the
construction of reasonable calculation models plays a fatal role in accurate
simulation, which should be closer to the real reaction system.
Fourth, according to the above summary, it is found that all non-Pt noble
metals, including Ru, Rh, Pd, Ag, Ir, and Au, show immense potential in hydrogen
generation at all pH ranges, typically Ru, Rh, Pd, and Ir. Nevertheless, until
now, in view of superb OER behavior, especially in acidic media, almost all
bifunctional non-Pt NMN electrocatalysts are only limited to Ir/Ru-involving
materials. For the larger cost reduction and convenience in the assembly of
electrolyzers, in the next step, more attention should be devoted to developing
more new and qualified bifunctional catalysts for both the OER and HER with high
activities under pH-universal conditions. Exploiting more novel regulation
tactics to concurrently activate the OER and HER in Rh, Pd, Ag, and Au or
integrating the OER-active material with the HER-active component provides
reasonable approaches to realize the bifunctionality of a catalyst.
Fifth, there is a lack of standardized measurements on the performance
comparison between different catalysts from different reports. For example, in
different research groups, the preparation methods of the working electrode, the
used catalyst loadings, methods for measuring stability, and methods to
calculate the specific activity or TOF highly differ, which makes the
performance evaluation of various materials more difficult and less meaningful.
Thus, in future studies, it is extremely imperative to encourage researchers to
test the HER properties under standard conditions and provide a unified
evaluation standard.
Lastly, to further meet pragmatic configurations of the electrolyzers, the
integration of binder-free 3D electrodes to electrolytic cells should be the
focus of future research. The design of 3D free-standing electrodes helps us to
promote faster charge transfer in the absence of low-conductivity binders and
largely suppress the electrode detachment, as well as afford more active sites.
Besides, the study of the large current density in the electrocatalysts also
should attract much attention in the future.
ACKNOWLEDGMENTS
M. Ni thanks the funding support (Project Nos. PolyU 152214/17E and PolyU
152064/18E) from the Research Grant Council, University Grants Committee, Hong
Kong SAR.
DATA AVAILABILITY
Data sharing is not applicable to this article as no new data were created or
analyzed in this study.
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