An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

doi:10.1016/j.jechem.2020.10.022

Journal of Energy Chemistry

Volume 59, August 2021, Pages 160-190

https://doi.org/10.1016/j.jechem.2020.10.022 Get rights and content

Highlights

•
Strategies to enhance the activity of noble-metal-free electrocatalysts are summarized.
•
Reasons behind activity increment owing to these modifications are discussed thoroughly.
•
Morphology modulation as an activity enhancement strategy is summerized for the first time.
•
Remaining research gaps and future prospects in this field are discussed in detail.

Abstract

The electrolysis of water for hydrogen generation has shown immense promise as an energy conversion technology for the green energy economy. Two concurrently occurring electrochemical reactions in water electrolysis (hydrogen and oxygen evolution reactions) are sluggish in nature and therefore the employment of electrocatalysts is highly essential. Noble-metal-based electrocatalysts (Pt, RuO₂, IrO₂, etc.) have shown superior activity towards these reactions. However, their lower natural abundance and inferior stability make the cost to performance ratio of water electrolysis too high. Thus, huge amount of research efforts are being carried out to develop electrocatalysts consisting of earth abundant elements (transition metals, carbon etc.) as the replacement of these noble-metal-based materials. Transition metal compounds, carbonaceous and hybrid materials have shown promise as efficient electrocatalysts but there is still huge gap between the activities of these materials and the noble-metal-based electrocatalysts. Several strategies like morphology modulation, elemental doping, defect engineering etc. are being deployed to enhance the activity of these noble-metal-free electrocatalysts. This review summarizes these strategies and thoroughly discusses the reason behind the changes in activity of the electrocatalysts owing to these modifications. Finally, the remaining research gaps and future prospects in this field are also discussed in detail.

Graphical abstract

This review summarizes the strategies which are being adopted to enhance the performance of the noble-metal-free electrocatalysts, discusses the reasons behind activity enhancement owing to these modifications and proposes future scopes in this research field.

Introduction

Ever-growing energy demand and environmental pollution motivated the researchers to develop a carbon–neutral energy economy [1]. Generation of hydrogen by water electrolysis has been proven to be a promising energy conversion technology to achieve that goal [1], [2]. The electrolysis of water involves two half-cell reactions: (1) hydrogen evolution reaction (HER) at cathode and (2) oxygen evolution reaction (OER) at anode [1], [3]. These two reactions involve several charge and proton transfer steps causing the whole water electrolysis process to be sluggish [4], [5]. Electrocatalysts are utilized to enhance the rate of these half-cell reactions and facilitate the water electrolysis process. Previous research efforts established the superior electrocatalytic water splitting activity of noble-metal-based materials [6]. The platinum (Pt) has been found to be the most efficient electrocatalyst for HER whereas the oxides of ruthenium and iridium (RuO₂ and IrO₂) show efficiency towards OER [6], [7]. Commercial-scale applicability of these noble-metal-based electrocatalysts is hindered by their low natural abundance and cost-effectiveness [7]. Over the past few decades, researchers are trying to reduce the price to performance ratio of the electrocatalysts in two ways: (1) by minimizing the noble-metal-loading in the electrocatalysts and (2) by developing noble-metal-free electrocatalysts [8]. The amount of noble metal in an electrocatalyst is being minimized by engineering various structural features [9], [10], [11]. In recent times, the most fascinating area of research is related to the development of noble-metal-free electrocatalysts [12], [13], [14]. The natural abundance of transition metals (specially the first row) and carbon is high as compared to the other elements in the periodic table. Therefore, most of the focuses are being deployed on the development of transition-metal-based and carbonaceous material-based electrocatalysts [15]. The transition-metal-based electrocatalysts are showing significant promise as the viable replacement of the noble-metal-based electrocatalysts [16], [17], [18]. Recently, the electrocatalytic water splitting activity of a series of materials is being investigated which can be categorized in the following way: (1) transition metal chalcogenides, pnictides, carbides and borides; (2) chemically modified carbonaceous materials like graphene, graphitic carbon nitride (g-C₃N₄) and carbon nanotubes (CNT); and (3) various heterostructures [19], [20], [21], [22], [23], [24], [25], [26], [27]. Selection of suitable noble-metal-free electrocatalyst is a crucial factor for further advancement in this field. A recently published review article has provided a systematic idea about the development of pentlandites, a new type of noble-metal-free electrocatalyst [28]. Although these noble-metal-free electrocatalysts showed promising electrocatalytic activity, there is still significant gap between the efficiency of these materials and the noble-metal-based electrocatalysts.

Three basic physicochemical steps occur during the electrocatalytic HER and OER: (1) adsorption of the active species on the catalytically active site, (2) transfer of charges from the electrocatalyst which causes some chemical changes in the active species and (3) desorption of the produced gas [5], [29], [30]. Therefore, the efficiency of an electrocatalyst depends on some of its intrinsic features like electrical conductivity, substrate adsorption efficiency, amount of accessible catalytically active sites, operational stability etc. The electrical conductivity and substrate adsorption efficiency of an electrocatalyst are directly related to its electronic structure [8], [31]. The catalytically active site accessibility of an electrocatalyst depends on its morphology [32], [33]. The operation stability of an electrocatalyst depends on various physicochemical aspects like chemical bonding, structural robustness etc. [34], [35]. Recently, the researchers are trying to enhance the activity of the noble-metal-free electrocatalysts following some innovative strategies like, morphology modulation, doping, defect engineering etc. [32], [33], [36], [37], [38], [39]. The elemental doping, strain, phase and defect engineering affect the electronic structure of a material and also increase the amount of catalytically active site in it [40], [41], [42], [43]. Development of an electrocatalyst with varied morphology alters the amount of accessible catalytically active sites [32], [33]. Formation of heterostructure between multiple transition metal compounds shows synergistic increment in electrocatalytic activity and the operational stability also increases [44], [45]. The amount of accessible catalytically active sites, charge transfer efficiency and stability of the transition metal-based materials increase when it forms heterostructure with carbonaceous materials [46], [47]. Several researchers have attempted to find out the relations between physicochemical modification of electrocatalysts and its catalytic activities with the help of in operand techniques and theoretical calculations [40], [48], [49], [50]. A comprehensive idea about these relations will help the researchers to make significant progress in the development of cheap electrocatalysts with efficiency comparable or superior to the noble-metal-based electrocatalysts.

This review summarizes the strategies to enhance the efficiency of the noble-metal-free materials towards water splitting. The implemented strategies are classified as: (1) morphology modulation, (2) doping, (3) defect engineering, (4) strain engineering, (5) phase engineering, and (6) heterostructure formation. In addition to these major strategies, some newly developed techniques are also discussed briefly in this review. It is noteworthy that, the morphology modulation is not systematically reviewed as an electrocatalytic activity enhancement strategy, till date. A few authors have tried to discuss the effectiveness of morphology modulation as catalytic activity enhancement strategy in their review articles [51], [52], [53]. However, either they have tried to focus this strategy from the point-of-view of different electrochemical reactions or have not established it to be a self-sufficient strategy for activity enhancement. They have considered the morphology modulation as an additional strategy which plays synergistically with other techniques like electronic modulation [53]. The relation between the above mentioned strategies and the corresponding change in catalytic activity has been discussed in detail. Finally, some challenges and future prospect in this research area has been discussed.

Section snippets

Electrochemical water splitting and electrocatalyst

Decomposition of water into hydrogen and oxygen due to the passage of electricity is termed as electrochemical water splitting or electrolysis of water [54], [55]. Like other electrochemical reactions, water splitting process can also be subdivided into two half-cell reactions. The reduction reaction i.e. the HER occurs at the cathode whereas the OER, the oxidation reaction, occurs at the anode [54], [55]. The generalized reactions can be represented as follows:HER: 4H₂O + 4e⁻ → 2H₂ + 4OH⁻OER:

Morphology modulation

Morphology modulation is an effective strategy to enhance the efficiency of an electrocatalyst in various aspects. The morphology modulation of the electrocatalyst has been started to overcome the potential drop due to the gas bubble formation on the electrode. This issue minimizes as the surface roughness and hydrophilicity of the electrocatalyst increase [71]. Modulating the morphology of an electrocatalyst can tune the amount of electrocatalytically active sites and charge transfer

Doping

Doping can effectively tune the intrinsic electronic structure of a material which affects its substrate adsorption capability and electrocatalytic activity [92]. Doping of foreign elements in a material creates lattice defects which can also significantly tune its electrocatalytic activity. In addition to that, introduction of defect enhances the amount of available electrocatalytically active centers in an electrocatalyst [93]. The following section discusses about the correlation between the

Defect engineering

Discussion from the previous section demonstrates that doping of any material with heterogeneous element might induce defects in it. These defect sites enhance the amount of catalytically active sites and facilitate the mass transfer process [43], [93], [97]. Defects can also be created in the lattice of a material without doping it with heteroatom. Few physicochemical processes like, ion irradiation, UV-ozone treatment, alkali etching etc. are utilized to introduce and engineer defects in

Strain engineering

Theoretical and experimental investigations show that the generation of strain in a material can effectively alter its electronic structure [69], [138]. As the electrocatalytic activity of a material is directly correlated with its electronic structure, it can be successfully tuned by strain engineering. Lattice strain in an electrocatalyst can be generated in several ways and the mechanical processes show higher potentiality. A lattice strain in an electrocatalyst is generated if mechanical

Phase engineering

The phase engineering has shown potentiality as electrocatalytic activity modulation technique for the transition-metal-based materials especially for the TMDs (such as CoSe₂, NiSe₂, MoS₂, MoSe₂ etc.) [149], [150], [151], [152], [153], [154], [155], [156], [157], [158], [159]. The electrical conductivity and substrate adsorption–desorption efficiency of an electrocatalyst is highest in its metallic phase as compared to the semi-metallic or semiconducting phase [149], [154], [159]. The phase

Heterostructure formation

Heterostructure formation is another widely adopted strategy to enhance the efficiency and stability of an electrocatalyst. Hybridization between two or more transition metal-based materials synergistically enhances their individual catalytic activity [164], [165], [166], [167], [168]. Bifunctional activity towards overall water splitting is achieved by combining one material active towards HER and other towards OER [167], [168]. The amount of active site and operational stability of a material

Other strategies

In addition to the previously discussed major strategies, some new techniques are also being adopted in recent times to enhance the activity of noble-metal-free electrocatalysts. Some worthy to mention strategies are: (1) electrochemical activation, (2) surface functionalization and (3) single atom anchoring [193], [194], [195], [196], [197].

WSe₂ obtained from colloidal synthesis process is electrochemically activated using H⁺ and alkali ions like Li⁺, Na⁺ and K⁺ [193]. This type of activation

Conclusions and outlook

The review discussed about the strategies being extensively utilized to enhance electrocatalytic activity of the noble-metal-free electrocatalysts. Tremendous research efforts of the past few years resulted in development of some cheap but efficient electrocatalysts consisting of earth-abundant elements. Table 1 summarizes the procedure or techniques researchers have undertaken to enhance the performance of the noble-metal-free-electrocatalysts. Table 2 demonstrates the change in

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors are thankful to the Director of CSIR-CMERI, Durgapur.

Subhasis Shit is currently pursuing PhD in Chemical Sciences under the supervision of Dr. Tapas Kuila and Dr. Naresh Chandra Murmu at the Surface Engineering & Tribology Division, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India. He completed his B.Sc in Chemistry from The University of Burdwan, West Bengal, India in 2014. He received his M.Sc in Chemistry from University of North Bengal, West Bengal, India in 2016. His research interest includes development of transition

References (201)

X. Zhong et al.
Electrochim. Acta
(2018)
J. Wang et al.
J. Alloys Compd.
(2020)
N. Yuan et al.
Arabian J. Chem.
(2020)
C. Zhang et al.
J. Alloys Compd.
(2020)
C. Xie et al.
Mater. Today
(2019)
Y. Zhou et al.
Appl. Catal., B
(2020)
S. Wang et al.
Appl. Surf. Sci.
(2018)
K. Zeng et al.
Prog. Energy Combust. Sci.
(2010)
Y. Wang et al.
Nano Today
(2017)
Y. Cheng et al.
Prog. Nat. Sci.: Mater. Int.
(2015)

J. Hwang et al.

Mater. Today

(2019)

B. Long et al.

Appl. Catal., B

(2019)

L. Fang et al.

J. Catal.

(2018)

M.M. Mohamed et al.

Int. J. Hydrogen Energy

(2019)

M. Zhu et al.

J. Colloid Interface Sci.

(2018)

K. Kordek-Khalil et al.

Appl. Surf. Sci.

(2020)

S.J. Marje et al.

J. Alloys Compd.

(2019)

Z. Yang et al.

Appl. Surf. Sci.

(2020)

H. Chu et al.

Appl. Catal., B

(2019)

Y. Zhang et al.

Catal. Commun.

(2015)

W. Yang et al.

J. Power Sources

(2019)

J.F. Qin et al.

J. Energy Chem.

(2019)

L. Yan et al.

Appl. Catal., B

(2020)

Z. Qiu et al.

Nano Energy

(2019)

B. You et al.

Acc. Chem. Res.

(2018)

J. Wang et al.

Adv. Mater.

(2016)

S. Jayabal et al.

J. Mater. Chem. A

(2017)

N.T. Suen et al.

Chem. Soc. Rev.

(2017)

H. Sun et al.

Adv. Mater.

(2020)

J. Zhang et al.

Angew. Chem. Int. Ed.

(2016)

X. Du et al.

Angew. Chem. Int. Ed.

(2019)

C. Zhu et al.

Angew. Chem. Int. Ed.

(2017)

H.N. Nong et al.

Chem. Sci.

(2014)

J.X. Wang et al.

Sci. Rep.

(2015)

Y. Jiao et al.

Chem. Soc. Rev.

(2015)

Y. Yan et al.

J. Mater. Chem. A

(2016)

M.A. Younis et al.

BMC Mat.

(2019)

X. Zou et al.

Chem. Soc. Rev.

(2015)

Z. Chen et al.

J. Mater. Chem. A

(2019)

D. Siegmund et al.

ChemElectroChem

(2020)

S. Anantharaj et al.

J. Mater. Chem. A

(2020)

X. Peng et al.

Sustainable Energy Fuels

(2019)

H. Du et al.

Nanoscale

(2018)

W.F. Chen et al.

Chem. Commun.

(2013)

Y. Jiang et al.

Nanoscale

(2020)

J. Li et al.

ChemCatChem

(2017)

Y. Xu et al.

Chem. Soc. Rev.

(2016)

G. Zhao et al.

Adv. Funct. Mater.

(2018)

V.I. Korobov et al.

C. Hu et al.

Energy Environ. Sci.

(2019)

Cited by (46)

MXenes and heterostructures-based electrocatalysts for hydrogen evolution reaction: Recent developments and future outlook
2024, Journal of Energy Chemistry
The increasing focus on electrocatalysis for sustainable hydrogen (H₂) production has prompted significant interest in MXenes, a class of two-dimensional (2D) materials comprising metal carbides, carbonitrides, and nitrides. These materials exhibit intriguing chemical and physical properties, including excellent electrical conductivity and a large surface area, making them attractive candidates for the hydrogen evolution reaction (HER). This scientific review explores recent advancements in MXene-based electrocatalysts for HER kinetics. It discusses various compositions, functionalities, and explicit design principles while providing a comprehensive overview of synthesis methods, exceptional properties, and electro-catalytic approaches for H₂ production via electrochemical reactions. Furthermore, challenges and future prospects in designing MXenes-based electrocatalysts with enhanced kinetics are highlighted, emphasizing the potential of incorporating different metals to expand the scope of electrochemical reactions. This review suggests possible efforts for developing advanced MXenes-based electrocatalysts, particularly for efficient H₂ generation through electrochemical water-splitting reactions..
The component-activity interrelationship of cobalt-based bifunctional electrocatalysts for overall water splitting: strategies and performance
2024, Journal of Energy Chemistry
Cobalt-based electrocatalysts take advantage of potentially harmonizable microstructure and flexible coupling effects compared to commercial noble metal-based catalytic materials. However, conventional water electrolysis systems based on cobalt-based monofunctional hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) catalysts have certain shortcomings in terms of resource utilization and universality. In contrast, cobalt-based bifunctional catalysts (CBCs) have attracted much attention in recent years for overall water splitting systems because of their practicality and reduced preparation cost of electrolyzer. This review aims to address the latest development in CBCs for total hydrolysis. The main modification strategies of CBCs are systematically classified in water electrolysis to provide an overview of how to regulate their morphology and electronic configuration. Then, the catalytic performance of CBCs in total-hydrolysis is summarized according to the types of cobalt-based phosphides, sulfides and oxides, and the mechanism of strengthened electrocatalytic ability is emphasized through combining experiments and theoretical calculations. Future efforts are finally suggested to focus on exploring the dynamic conversion of reaction intermediates and building near-industrial CBCs, designing advanced CBC materials through micro-modulation, and addressing commercial applications.
Recent progress in hydrogen: From solar to solar cell
2024, Journal of Materials Science and Technology
Hydrogen, meeting the requirements of sustainable development, is regarded as the ultimate energy in the 21st century. Due to the inexhaustible and feasible of solar energy, solar water splitting is an immensely promising strategy for environmental-friendly hydrogen production, which not only overcomes the fluctuation and intermittency but also contributes to achieving the mission of global “Carbon Neutrality and Carbon Peaking”. However, there is still a lack of a comprehensive overview focusing on hydrogen progress with a discussion of development from solar energy to solar cells. Herein, we emphasize several solar-to-hydrogen pathways from the basic concepts and principles and focus on photovoltaic-electrolysis and photoelectrochemical/photovoltaic systems, which have achieved solar-to-hydrogen (STH) efficiency of over 10% and have extremely promising for large-scale application. In addition, we summarize the challenges and opportunities faced in this field including configuration design, electrode materials, and performance evaluation. Finally, perspectives on the potential commercial application and scientific research for the further development of solar-to-hydrogen are analyzed and presented.
In situ infrared, Raman and X-ray spectroscopy for the mechanistic understanding of hydrogen evolution reaction
2024, Journal of Energy Chemistry
Hydrogen production by water reduction reactions has received considerable attention because hydrogen is considered a clean-energy carrier, key for a sustainable energy future. Computational methods have been widely used to study the reaction mechanism of the hydrogen evolution reaction (HER), but the calculation results need to be supported by experimental results and direct evidence to confirm the mechanistic insights. In this review, we discuss the fundamental principles of the in situ spectroscopic strategy and a theoretical model for a mechanistic understanding of the HER. In addition, we investigate recent studies by in situ Fourier transform infrared (FTIR), Raman spectroscopy, and X-ray absorption spectroscopy (XAS) and cover new findings that occur at the catalyst–electrolyte interface during HER. These spectroscopic strategies provide practical ways to elucidate catalyst phase, reaction intermediate, catalyst-electrolyte interface, intermediate binding energy, metal valency state, and coordination environment during HER.
Underlying aspects of surface amendment strategies adopted in electrocatalysts for overall water splitting under alkaline conditions
2024, Current Opinion in Electrochemistry
Hydrogen (H₂) is a well-known and efficient energy carrier that can be utilized as future green fuel. H₂ production via electrolysis of water can be considered as the most suitable energy conversion technology. For water electrolysis, the competent catalysts are noble metal-associated electrocatalysts such as Pt, RuO₂, IrO₂, etc. Due to their high cost and scarcity-to-performance ratio, intense research is being carried out for the fabrication of inexpensive, stable, and extremely active transition metal-based electrocatalyst for water electrolysis. In this context, surface modification strategies such as nanostructure engineering, introducing doping elements, defects or vacancies, and composition modulation for enhancing electrocatalysts properties are highly pursued in the recent literature. These strategies contribute to the modification of electronic structure, boosting electronic conductivity, and enhancing the exposure of catalytically active sites. This review reports the recent progress on various synergistic surface modulation aspects for advancing the catalyst’s performance for overall water electrolysis in alkaline media.
Highly durable monolithic electrode for water electrolysis at industrial current densities
2024, Nano Energy
The development of highly durable electrode with current density over 500 mA cm⁻² is the key to realize low-energy-cost industrial water electrolysis. While the dramatical gas evolution environment with high current makes the electrode more likely to suffer from severe dropping and loss of catalytic active components. Hence, it is of great significance but challenge to develop robust monolithic electrode with both high activity and durability in water electrolysis. Herein, we design an edge-rich monolithic electrode via in-situ construction of molybdenum disulfide and nickel disulfide heterogeneous interfaces on nickel foam (ER-MoSNi) for extraordinary water electrolysis. The bifunctional ER-MoSNi monolithic electrode incorporated two-electrode water electrolyzer with 1.0 M KOH solution at 25 °C requires ultralow cell voltage of 2.08 V@1000 mA cm⁻², far exceeding the Pt/C supported on nickel foam as cathode and IrO₂ supported on nickel foam as anode of 2.6 V@1000 mA cm⁻². Moreover, the ER-MoSNi monolithic electrode can operate stably for over 2500 h at a current density of 1000 mA cm⁻², which is significant super to Pt/C║IrO₂. The great advantages of the ER-MoSNi monolithic electrode in the activity and durability have shown great potential in the field of industrial water electrolysis.

View all citing articles on Scopus

Saikat Bolar completed his B.Sc in Chemistry from The University of Burdwan, West Bengal, India in 2013. He received his M.Sc in Chemistry from Sidho-Kanho-Birsha University, Purulia, India, 2015. He qualified the NET (National Level Eligibility Test) conducted by CSIR, New Delhi. He is currently pursuing his PhD from Academy of Scientific and Innovative Research (AcSIR) in Chemical Sciences under the supervision of Dr. Tapas Kuila and Dr. Pranab Samanta at the Surface Engineering & Tribology Division, CSIR-Central Mechanical Engineering Research Institute, Durgapur, India. Currently he is working on transition metal dichalcogenide - MoS₂ based Electrocatalyst for hydrogen evolution reaction in different pH medium.

Dr Naresh Chandra Murmu is working as a Senior Principal Scientist in CSIR – Central Mechanical Engineering Research Institute, Durgapur since 2003. Previously he was a Scientist in the National Aerospace Laboratories, Bangalore for 9 years. He received his B.E. from Calcutta University in 1992, M.E. from IISc Bangalore in 1994 and Ph.D. in Mechanical Engineering from IIT (BHU), Varanasi in 2010. He has published over 87 research/review articles in peer reviewed journals and 4 book chapters. Dr Murmu is the recipient of the prestigious National Design Award (2012), CSIR-Raman Research Fellowship (2012) and DAAD Fellowship (2001) among many awards and honors.

Dr. Tapas Kuila is working as Senior Scientist at CSIR-Central Mechanical Engineering Research Institute,Durgapur, India. Dr. Kuila completed PhD in Chemistry from Indian Institute of Technology, Kharagpur in 2009. Then, he moved to Chonbuk National University, South Korea for postdoctoral study. Dr. Kuila is working in the areas of graphene supercapacitor, graphene/epoxy composite, graphene lubricant, electrocatalytic water splitting, and graphene enhanced phase change materials. He has published ~133 research/review articles in different international peer-reviewed journals. Dr. Kuila also authored 17 book chapters 3 Indian patents.

View full text

ReviewAn account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Electrochemical water splitting and electrocatalyst

Morphology modulation

Doping

Defect engineering

Strain engineering

Phase engineering

Heterostructure formation

Other strategies

Conclusions and outlook

Declaration of Competing Interest

Acknowledgments

Electrochim. Acta

J. Alloys Compd.

Arabian J. Chem.

J. Alloys Compd.

Mater. Today

Appl. Catal., B

Appl. Surf. Sci.

Prog. Energy Combust. Sci.

Nano Today

Prog. Nat. Sci.: Mater. Int.

Mater. Today

Appl. Catal., B

J. Catal.

Int. J. Hydrogen Energy

J. Colloid Interface Sci.

Appl. Surf. Sci.

J. Alloys Compd.

Appl. Surf. Sci.

Appl. Catal., B

Catal. Commun.

J. Power Sources

J. Energy Chem.

Appl. Catal., B

Nano Energy

Acc. Chem. Res.

Adv. Mater.

J. Mater. Chem. A

Chem. Soc. Rev.

Adv. Mater.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

Angew. Chem. Int. Ed.

Chem. Sci.

Sci. Rep.

Chem. Soc. Rev.

J. Mater. Chem. A

BMC Mat.

Chem. Soc. Rev.

J. Mater. Chem. A

ChemElectroChem

J. Mater. Chem. A

Sustainable Energy Fuels

Nanoscale

Chem. Commun.

Nanoscale

ChemCatChem

Chem. Soc. Rev.

Adv. Funct. Mater.

Energy Environ. Sci.

Review
An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts