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Developing noble-metal-free bifunctional electrocatalysts at an effective cost and with a high catalytic ability for hydrogen production via water-splitting is imperative, although a great bottleneck remains. Herein, we present a plasma engraving strategy to synthesize N-doped CoFeS on cobalt foam with a multi-interface and defect hierarchical structure. The N-doped CoFeS was synthesized using an ion exchange method to prepare the CoFe LDH precursor, followed by sulphidation and plasma-assisted engraving in nitrogen gas. The N-doped CoFeS requires an overpotential of 230 mV for the OER and 26 mV for the HER to reach a current density of 10 mA cm−2. It also shows an excellent catalytic activity towards overall water splitting, which requires a low voltage of 1.61 and 1.80 V to achieve a current density of 10 and 50 mA cm−2, respectively, in 1 M KOH. The super-catalytic properties can be attributed to the interface and defect structure, which induces a high intrinsic activity, a superior transfer coefficient, and abundant active sites. This work presents a novel approach to prepare noble-metal-free electrocatalyst with plenty of interface and defect sites for overall water splitting. [ABSTRACT FROM AUTHOR]

Combining the self‐sacrifice of a highly crystalline substance to design a multistep chain reaction towards ultrathin active‐layer construction for high‐performance water splitting with atmospheric‐temperature conditions and an environmentally benign aqueous environment is extremely intriguing and full of challenges. Here, taking cobalt carbonate hydroxides (CCHs) as the initial crystalline material, we choose the Lewis acid metal salt of Fe(NO3)3 to induce an aqueous‐phase chain reaction generating free CO32− ions with subsequent instant FeCO3 hydrolysis. The resultant ultrathin (∼5 nm) amorphous Fe‐based hydroxide layer on CCH results in considerable activity in catalyzing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), yielding 10/50 mA ⋅ cm−2 at overpotentials of 230/266.5 mV for OER and 72.5/197.5 mV for HER. The catalysts can operate constantly in 1.0 M KOH over 48 and 45 h for the OER and HER, respectively. For bifunctional catalysis for alkaline electrolyzer assembly, a cell voltage as low as 1.53 V was necessary to yield 10 mA cm−2 (1.7 V at 50 mA cm−2). This work rationally builds high‐efficiency electrochemical bifunctional water‐splitting catalysts and offers a trial in establishing a controllable nanolevel ultrathin lattice disorder layer through an atmospheric‐temperature chemical route. [ABSTRACT FROM AUTHOR]

Interfacial structure engineering with multiple high‐oxidation‐state cations, especially those that show unstable higher‐valence during catalysis towards superior electron synergy, for high‐performance electrocatalysis is of great interest and full of challenges. Lattice distortion from lattice strain at phase boundaries as a result of interfacial structure engineering is also appealing. Fe oxyhydroxide containing Fe3+ lead to unstable Fe4+ with a short lifetime on edge/defect sites during steady‐state water‐oxidation catalysis. Such material was deliberately installed to achieve atom‐scale combination with Ni3+ relevant layered double hydroxide to construct high‐energy interfaces for high‐oxidation‐state cations synergy and induce lattice distortion. The Fe‐o‐NiAlOH exhibited prominent property toward oxygen evolution reaction with 202 mV to drive 10 mA cm−2. Fe‐o‐NiAlOH also showed hydrogen evolution reaction activity, requiring an overpotential of 180 mV for 10 mA cm−2. Alkaline water electrolyzer with Fe‐o‐NiAlOH as both anodic and cathodic electrodes required only 1.64 V to reach 10 mA cm−2. This work offers an effective well‐defined electrocatalyst and shows the synergetic protocol of unstable high‐oxidation‐state cations and lattice defects for high‐performance water decomposition catalysis. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a clean and sustainable process for hydrogen production on a large scale as the electrical power required can be obtained from various renewable energy resources. The key challenge in electrochemical water splitting process is to develop low‐cost electrocatalysts with high catalytic activity for the hydrogen evolution reaction (HER) on the cathode and the oxygen evolution reaction (OER) on the anode. OER is the most important half‐reaction involved in water splitting, which has been extensively studied since the last century and a large amount of electrocatalysts including noble and non‐noble metal‐based materials have been developed. Among them, transition metal borides and borates (TMBs)‐based compounds with various structures have attracted increasing attention owing to their excellent OER performance. In recent years, many efforts have been devoted to exploring the OER mechanism of TMBs and to improving the OER activity and stability of TMBs. In this review, recent research progress made in TMBs as efficient electrocatalysts for OER is summarized. The chemical properties, synthetic methodologies, catalytic performance evaluation, and improvement strategy of TMBs as OER electrocatalysts are discussed. The electrochemistry fundamentals of OER are first introduced in brief, followed by a summary of the preparation and performance of TMBs‐based OER electrocatalysts. Finally, current challenges and future directions for TMBs‐based OER electrocatalysts are discussed. [ABSTRACT FROM AUTHOR]

Novel nanomaterials and advanced nanotechnology continuously push forward the rapid development of sustainable energy conversion and storage equipment. An emerging family of two‐dimensional transition‐metal carbides, nitrides and carbonitrides, also known as MXenes, have attracted increasing attention and in depth investigation. Benefitting from their unique intrinsic properties, MXenes have attracted significant attention and they have been considered as promising candidate materials for the development of environmentally friendly energy resources. A large number of studies show that MXenes have great potential in energy conversion and storage fields. Despite of their exceptional properties, MXenes also have some inherent characteristics, such as low capacities and unstable retention performances, which severely hinder their prospect applications in energy conversion and storage fields. In this Minireview, the latest progress on MXenes and their hybrid composites with small molecules, polymers, carbon or metal ions, and their applications in energy conversion and storage fields is highlighted, including their use in different types of batteries, supercapacitors, hydrogen/oxygen evolution reactions, electromagnetic interference absorption/shielding and solar steam generation. In addition, the critical challenges and further development prospects of MXene‐based materials are also introduced. [ABSTRACT FROM AUTHOR]

[Display omitted] • The basic factors for evaluating catalyst electrochemical water separation performance are systematically summarized and generalized, with each basic parameter explained in detail. • The synthesis strategies and structural optimization of MOF-based and MOF-derived materials in the recent years are summarized and categorized. • The advantages and drawbacks of the electrolytic water performance of MOF-based and MOF-derived materials of different methods are presented. • The obstacles and potential developments in the challenges of designing and commercializing of MOF-based and MOF-derived materials are explored. Water-splitting electrocatalysis has gained increasing attention as a promising strategy for developing renewable energy in recent years, but its high overpotential caused by the unfavorable thermodynamics has limited its widespread implementation. Therefore, there is an urgent need to design catalytic materials with outstanding activity and stability that can overcome the high overpotential and thus improve the electrocatalytic efficiency. Metal-organic frameworks (MOFs) based and/or derived materials are widely used as water-splitting catalysts because of their easily controlled structures, abundant heterointerfaces and increased specific surface area. Herein, some recent research findings on MOFs-based/derived materials are summarized and presented. First, the mechanism and evaluation parameters of electrochemical water splitting are described. Subsequently, advanced modulation strategies for designing MOFs-based/derived catalysts and their catalytic performance toward water splitting are summarized. In particular, the correlation between chemical composition/structural functionalization and catalytic performance is highlighted. Finally, the future outlook and challenges for MOFs materials are also addressed. [ABSTRACT FROM AUTHOR]

Pt clusters assembled on Mo doped NiO x nanosheet arrays (Pt/Mo-NiO x) is prepared on the surface of NiMo foam (NMF) by an efficient light-driven redox reaction. The Pt/Mo-NiO x /NMF electrode exhibits outstanding alkaline HER activity with low overpotential of only 62 mV to achieve the current density of 100 mA cm−2. [Display omitted] Designing cost-effective alkaline hydrogen evolution reaction (HER) catalysts with high water dissociation ability, enhanced hydroxyl transfer rate and optimized hydrogen adsorption free energy (ΔG H*) by a time and energy efficient strategy is pivotal, but still challenging for alkaline water electrolysis. Herein, Pt/Mo-NiO x hybrid consisting of Pt clusters assembled on Mo-doped NiO x nanosheet arrays is prepared on the surface of raw NiMo foam (NMF) by a light-driven strategy to address this challenge. Benefitting from the electronic interaction between Mo-NiO x and Pt, the Pt/Mo-NiO x composite owns optimized ΔG H* and is beneficial for accelerating water dissociation and hydroxyl transfer. As a result, the optimized Pt/Mo-NiO x /NMF electrode displays an exceptional alkaline HER activity with a low overpotential of 62 mV to obtain 100 mA cm−2 and a high Pt mass activity (13.2 times as high as that of commercial 20 wt% Pt/C). Furthermore, the assembled two-electrode cell of Pt/Mo-NiO x /NMF||NiFe-LDH/NF requires a voltage of only 1.549 V to deliver 100 mA cm−2, along with negligible activity decay after 70 h stability test. The present study provides a promising strategy for exploiting high-performance electrocatalysts towards alkaline HER. [ABSTRACT FROM AUTHOR]

The development of cost-effective non-precious metal bifunctional electrocatalysts with performance comparable to that of precious metal-based catalysts is an important factor in achieving industrial hydrogen production from electrolytic water. In order to prepare electrocatalysts with highly exposed active sites and high intrinsic activity, unique heterostructure and element doped 2D Co–NiS 2 /CeO 2 nanosheets grown on foamed nickel (Co–NiS 2 /CeO 2 /NF) are prepared by hydrothermal reaction and annealing. The Co–NiS 2 /CeO 2 /NF catalyst demonstrates excellent performance and stability in alkaline solutions. In 1.0 M KOH solution, the overpotentials for the HER and OER were found to be as low as 88 mV and 240 mV, respectively. Moreover, when utilized as both the anode and cathode in a standard two-electrode water electrolyzer, Co–NiS 2 /CeO 2 /NF delivers 50 mA cm−2 at a relatively low voltage of 1.82 V and was able to maintain its high performance levels without any degradation even after 48 h of CP test. The combination of doping and interfacial effects greatly increases the number of active sites and the activity of the catalyst. This study provides a new pathway for the design of cost-effective, high-performance catalytic materials for overall water splitting. Co-doped and CeO 2 heterostructure modified NiS 2 grown on foamed nickel electrocatalyst is successfully constructed through a simple hydrothermal process followed by further vulcanization treatment and exhibits excellent electrocatalytic performance and stability towards overall water splitting. In 1.0 M KOH solution, the current densities of the HER and OER can reach 10 mA cm−2 with minimum overpotentials of 88 mV and 240 mV, respectively. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing Co–NiS 2 /CeO 2 /NF as both the cathode and anode, it can generate 10 mA cm−2 at 1.38 V and operate steadily without performance degradation after 48 h. [Display omitted] • The combination of doping and interfacial effects greatly increases the activity of the catalyst. • Co–NiS 2 /CeO 2 /NF exhibits excellent activity towards overall water splitting. • Co–NiS 2 /CeO 2 /NF shows a remarkably stability with a nearly unchanged potential after a longer stability test. [ABSTRACT FROM AUTHOR]

Catalysts of multiphase nickel sulfide coupling with CeO 2 (NiS x /CeO 2 /NF) are fabricated through one step hydrothermal and calcination process. The as-obtained NiS x /CeO 2 /NF exhibits excellent activity towards overall water splitting reaction with a low potential of 1.53 V for 10 mA cm−2 in 1 M KOH. [Display omitted] Constructing nanostructured electrocatalysts with heterointerface and finetuning their electronic properties are essential for high-efficient overall water splitting. Here, we prepared a well-designed nano-flower-like multiphase and hybrid material of NiS/NiS 2 /CeO 2 /NF (NiS x /CeO 2 /NF) with rich heterointerfaces and abundant active sites through solvothermal reaction and post-annealing treatment. The as-fabricated NiS x /CeO 2 /NF exhibits exceptional catalytic performance for OER and HER. Specifically, in 1 M KOH solution, it requires the low overpotentials of 326 and 92 mV to achieve the current density of 200 and 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. More satisfactorily, when NiS x /CeO 2 /NF is used as the bifunctional catalyst, a low voltage of only 1.53 V is required to achieve a current density of 10 mA cm−2 for overall water splitting. The excellent catalytic performance should be attributed to its special heterogeneous structure and the synergy effect between NiS x and CeO 2. This work emphasizes the important significance of constructing efficient bifunctional electrocatalysts by reasonably designing heterostructures and multiphase components for overall water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bifunctional catalyst (V-NiSe) is successfully synthesized by introducing V atoms into NiSe. • The electron structure of NiSe can be optimized by introducing V to interfere with the electronic environment around Ni atoms. • The V-NiSe nanorods exhibit distinguished catalytic activity and cyclic stability for overall water splitting. Adjusting the electronic structure and intrinsic activity of the active site of the catalyst based on atomic implantation is the crucial to realizing efficient electrochemical water splitting in alkaline media. Thus, we introduce vanadium (V) atoms with abundant vacant d orbitals as dopants into nickel selenides (NiSe), which has abundant variable valence states, and successfully synthesise three-dimensional bi-functional catalysts self-supported on Ni foam (NF). The electron structure characterisation reveals that, compared with the pure NiSe phase, the oxidation states of Ni cations and electron concentration at the Se site in V–NiSe increase due to the V doping. These changes are accompanied by changes in the electronic structure and active sites in V–NiSe. The as-generated V–NiSe nanorods exhibit an optimised electronic structure, high number of active sites and highly rough nanorod array structure with large electrochemically active surface area and in situ growth characteristics of conductive NF. Thus, the as-generated V–NiSe nanorods catalysts exhibit excellent bi-functional catalytic activity, with 50 mA⋅cm−2 at an overpotential of 270.2 and 251.2 mV for oxygen evolution reactions (OER) and hydrogen evolution reactions (HER), respectively, in KOH (1 M). Water electrolysis using V–NiSe as both the anode and cathode requires a cell voltage of 1.76 V to drive 50 mA⋅cm−2, continuously operating for 80 h. This study provides a systematic understanding of the design of transition-metal catalysts using heteroatomic doping to control their electronic structure and catalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] Designing heterojunction catalysts with energy effects at the interface, particularly combining the surface structure advantages of super-hydrophilic interfaces with the high activity advantages of bimetal synergistic optimisation, is the key to developing economical and efficient industrial electrocatalytic water-splitting catalysts. In this study, a coupled nanoflower-like NiFe(OH) x /(Ni, Fe)Se heterostructure catalyst supported on Ni foam (NF) (NFSe@NFOH/NF) was designed and successfully prepared using hydrothermal and electrodeposition strategies. Owing to the electron interaction at the heterogeneous amorphous (NFOH)/crystalline (NFSe) interface and the bimetallic synergistic effect of Ni and Fe, the prepared NFSe@NFOH/NF exhibited excellent and stable oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalytic properties, with low overpotentials of 214/276 mV at 100 mA⋅cm−2 and 262/340 mV at 500 mA⋅cm−2. The assembled water electrolyser comprising NFSe@NFOH/NF || NFSe@NFOH/NF needed only small voltages of 1.73 and 1.85 V to yield current densities of 100 and 500 mA⋅cm−2, respectively. This study offers an innovative design idea for the rational adoption of interface engineering and amorphous–crystalline engineering techniques to construct catalysts with excellent catalytic activity and stability for electrocatalytic overall water splitting (EOWS) at a high current density, which further facilitates the advancement of sustainable energy technology in the future. [ABSTRACT FROM AUTHOR]

Ru@Fe-Ni(OH) 2 /NF catalyst fabricated through Fe-doped and interfacial Ru nanoclusters co-engineering of Ni(OH) 2 nanosheets directly grafted on Ni foam exhibits excellent activity towards oxygen evolution reaction (OER) in alkaline media with an overpotential of 266.4 mV to achieving a current density of 50 mA cm−2 in 1 M KOH. Our results show that we have successfully developed an efficient OER catalyst for green and efficient electrocatalytic hydrolysis to produce H 2 and O 2 , providing a promising method for clean H 2 production. [Display omitted] The creation of inexpensive, high-performance catalysts to reduce the overpotential of the oxygen evolution reaction (OER) process is critical for the electrolysis of water for hydrogen production. Therefore, we applied a one-step hydrothermal method using cation exchange reaction (CER) to prepare Fe-doped and interfacial Ru nanoclusters co-engineered Ni(OH) 2 nanosheets directly grafted on Ni foam (Ru@Fe-Ni(OH) 2 /NF) for OER process. Results of electrochemical tests reveal that Ru@Fe-Ni(OH) 2 /NF has excellent OER activity, and its overpotential (η) is only 266.4 mV when the current density is 50 mA cm−2 in 1 M KOH solution, even lower than that of commercial OER catalyst RuO 2 (355 mV). The Tafel slope also decreases from 133.8 mV dec−1 for pristine Ni(OH) 2 /NF material to 24.1 mV dec−1 for Ru@Fe-Ni(OH) 2 /NF, indicating the higher charge transfer rates and fastest kinetics for water oxidation. At an overpotential of 300 mV the optimal turnover frequency (TOF) of 0.062 s−1 for Ru@Fe-Ni(OH) 2 /NF is achieved compared to that of Ni(OH) 2 /NF (0.014 s−1, NN), demonstrating the fast reaction kinetics of the as-prepared electrocatcalyst. After 24 h stability test, the catalytic activity of Ru@Fe-Ni(OH) 2 /NF was only attenuated by 2 %, showing excellent OER stability and durability. Our results show that we have successfully developed an efficient OER catalyst for green and efficient electrocatalytic hydrolysis to produce H 2 and O 2 , providing a promising method for clean H 2 production. [ABSTRACT FROM AUTHOR]

[Display omitted] • This study realizes rational construction of the hierarchical wing-like iron/molybdenum oxide heterojunction on nickel foam (FMO/NF). • Hierarchical porous structure composed of the nanoparticle-micron sheets facilitates electrolyte/catalyst contact and bubble release. • The synergistic effect of Fe and Mo combined with the interfacial effect of the heterojunction optimizing structural configurations. • FMO/NF exhibits distinguished performance for overall water splitting in alkaline solution. Designing heterojunction catalysts with high-energy interfacial effects, especially combining the geometrical advantages of hierarchical micro-nano structures with the advantages of bi- or multi-metal syergistically optimised electronic coordination environments, is crucial for achieving efficient and stable water splitting. In this study, a simple one-step hydrothermal method was used to construct a hierarchical wing-like iron/molybdenum oxide heterojunction with a porous structure on nickel foam (FMO/NF). The synergistic effect of Fe, Mo, and the heterostructures can enrich structural defects, overcome the disadvantages of the individual components, and improve material performance by optimising the structural configurations and electronic properties and exploiting the electronic interactions that occur between interfaces composed of different phases. In addition, owing to the high porosity of the hierarchical micro-nano structure and abundant active sites, the wing-like FMO/NF was utilised as an efficient bifunctional catalyst for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), presenting low overpotentials of 278.06 and 263.72 mV, respectively, at a current density of 100 mA·cm−2 in 1 mol/L KOH. Furthermore, assembling FMO/NF as both the anode and cathode (FMO/NF || FMO/NF) required a cell voltage of 1.87 V to drive 100 mA·cm−2 in 1 mol/L KOH, and it proceeded continuously for 110 h with negligible cell voltage decay. This work provides a rational synthetic route for the preparation of innovative double transition metal-based micro-nano hierarchical heterostructured electrocatalysts with a synergistic effect and further advances the development of energy-conversion technology. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploration of highly efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is of crucial importance for the development of water splitting. In recent years, Cu-based materials have been widely concerned in OER due to their non-toxicity, rich reserves and highest reversibility. Meanwhile, Cu x O nanorods is easy to be prepared in industry. Herein, we report a fast preparation method to construct an integrated Cu x O@CoNi-LDH electrocatalyst with a unique 1D nanowire-2D nanosheet hierarchical core–shell structure by electrodepositing CoNi-LDH nanosheet arrays directly onto Cu x O nanorods (Cu x O were in situ-created on the Cu foam) at a large deposition voltage of −3.0 V vs SCE. The unique heterogeneous core–shell nanostructure, large deposition amount of CoNi-LDH and the synergistic effects between Cu x O core and CoNi-LDH shell can provide abundant active sites, rich open-channels and reduced charge transfer resistance (R ct) for effective oxygen release and facile electron transport. Consequently, the optimized Cu x O@CoNi-LDH/CF exhibits a low overpotential of 207 mV in 1 M KOH solution at the current density of 10 mV cm−2 and a small Tafel slope of 50.1 mV dec−1. After 60 h of long-term stability test, the catalytic performance is only slightly weakened. This work demonstrates a new approach to design the high-performance LDH and Cu-related OER catalysts by constructing a unique hierarchical core–shell nanostructure. [ABSTRACT FROM AUTHOR]

[Display omitted] Heteroatom doping is considered a typical method for improving the electrochemical properties of composites. In this work, the multi-component oxide catalyst (Ni(VO 3) 2 and Co 2 V 2 O 7 on Ni foam, referred to as NiCoVO x @NF) is formed by hydrothermal doping of V element into NiCo-based precursors followed by co-oxidation. In the catalyst NiCoVO x @NF, all three components of Ni, Co and V are particularly tightly coordinated, exhibiting an integrated structure of keel flower-like arrays. The catalyst NiCoVO x @NF's contact surface with water is increased thanks to this unusual structure, exposing a high number of active sites. Furthermore, NiCoVO x @NF owns efficient electronic pathways, which greatly enhances the electron transport ability. To generate a current density of 10 mA cm−2 for hydrogen evolution reaction, just a 107 mV overpotential is required. The electrode exhibits a low overpotential of 217 mV to deliver 50 mA cm−2 for oxygen evolution reaction. In addition, the total water splitting performance of NiCoVO x @NF is also excellent, which could be achieved by only one 1.5 V AA battery. This study provides a feasible heteroatom doping route to design bifunctional catalysts with improved performances. [ABSTRACT FROM AUTHOR]

Interfacial charge redistribution induced by a strong built-in electric field can expertly optimize the adsorption energy of hydrogen and hydroxide for improving the catalytic activity. Herein, we develop a well-defined hierarchical NiFe 2 O 4 /NiFe layered double hydroxides (NFO/NiFe LDH) catalysts, exhibiting superior performance due to the strong interfacial electric field interaction between NiFe 2 O 4 nanoparticle layers and NiFe LDH nanosheets. In 1 M KOH, NFO/NiFe LDH needs 251 mV and 130 to drive 50 and 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Moreover, only 1.517 V cell voltage is needed to reach 10 mA cm−2 towards overall water splitting. Notably, under simulated industrial electrolysis conditions, NFO/NiFe LDH only needs 289 mV to drive 1000 mA cm−2. This work puts a deep insight into the role of the built-in electric field in transition metal-based catalysts for accelerating water splitting and scalable industrial electrolysis applications. Interfacial charge redistribution induced by built-in electric field can improve the catalytic activity. A well-defined hierarchical NiFe 2 O 4 /NiFe LDH catalyst is successfully constructed by a hydrothermal coordination strategy. The catalyst exhibits excellent activities for oxygen evolution reaction with a low overpotential of 251 mV at 50 mA cm−2 and hydrogen evolution reaction with 130 mV overpotential at 10 mA cm−2 in 1 M KOH. Moreover, merely 1.517 V cell voltage is required to drive 10 mA cm−2 current density for overall water splitting. [Display omitted] • NiFe 2 O 4 /NiFe LDH is fabricated through a one-pot hydrothermal methodology. • NiFe 2 O 4 /NiFe LDH exhibits prominent OER and HER performance and excellent stability. • NiFe 2 O 4 /NiFe LDH achieves efficient water oxidation at the large current density. • Interfacial charge redistribution and defects in oxides attributed to high catalytic property. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlled escape of Ni atoms is adopted to create an ion-bath microenvironment in which multiple high-valence ions coexist. • The timeline-adjusted ion-bath microenvironments effectively trigger the transformation of NFCH to ultra-thin porous nickel ferrite intercalated NFCH nanosheets. • The ultra-thin porous NF-CH-O nanosheets exhibit distinguished performance for overall water splitting at high current densities. Precisely tailoring the structure of inorganic materials at the micron and nanometer scales, especially in collaboration with component customization to design efficient, stable and low-cost transition-metal-based catalysts for industrial electrocatalytic water splitting (EWS) is a key renewable energy technology, but still facing a daunting challenge. Here, the controllable escape of Ni atom is adopted to disturb the hydrothermal ion-bath environment, thereby resulting in the coexistence of high valence Ni and Fe ions. Combined with a one-step hydrothermal coordination strategy, the timeline-adjusted ion-bath microenvironment can effectively trigger the phase transformation of carbonate hydroxide hydrate nanosheets (NFCH) to nickel ferrite intercalated NFCH ultra-thin porous nanosheets (NF-CH-O). Thanks to the high-energy phase boundary synergistic effect and the rapid mass transfer advantages of ultra-thin porous nanostructures, the as-prepared NF-CH-O nanosheets exhibit remarkable oxygen and hydrogen evolution reaction (OER/HER) catalytic activity and stability, with low overpotentials of 207/191 mV at 50 mA cm−2, respectively, as well as the activity retention for 100 h. The alkaline water electrolyzer set up with NF-CH-O as both anodic and cathodic electrodes only requires a cell potential of 1.688 V to reach 50 mA cm−2 in a continuous operation of 100 h. More impressively, NF-CH-O only requires overpotentials of 266, 292 mV and 1.877 V to drive high current densities up to 500 mA cm−2 for OER, HER and EWS, respectively, and exhibits excellent stability with a reduction in the activity of less than 10% over cycles of more than 65 h. This work highlights the room-temperature controllable ion-bath oxidative etching strategy to design efficient bifunctional catalysts with ultra-thin porous structure and high-current–density activity. Meanwhile, combined with the advantages of direct growth on the substrate for mass production, such meticulous consideration of nanostructured design will be more competitive in the H 2 -production industry. [ABSTRACT FROM AUTHOR]

Interface engineering has aroused vitally widespread concern since it could be an effective strategy for exploring high-performance and low-cost water oxidation electrocatalysts. Herein, we report a hetero-structured Ni 3 (NO 3) 2 (OH) 4 /CeO 2 /NF (NNO/CeO 2 /NF) electrode, exhibiting superior performance owning to the NO 3 − anion substitution for the OH− in nickel hydroxide to form Ni 3 (NO 3) 2 (OH) 4 , together with its interface synergy with ceria. In alkaline solution, the NNO/CeO 2 /NF electrocatalyst could catalyze the OER with an overpotential of 330 mV to approach 50 mA cm−2. Also, it needs only an overpotential of 120 mV to reach 10 mA cm−2 for HER. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing NNO/CeO 2 /NF as both the cathode and anode, it can generate 10 mA cm−2 at 1.64 V and operate steadily without performance degradation after 25 h. This research provides a novel perspective for reasonable design of advanced catalytic materials with improvements in the field of electrocatalysis. Combining strong coupling and synergistic effect at different component boundaries, flower-like Ni 3 (NO 3) 2 (OH) 4 /CeO 2 /NF catalyst is successfully constructed by a hydrothermal coordination strategy. The catalyst exhibits excellent electrocatalytic activities toward oxygen evolution reaction with a low overpotential of 330 mV at 50 mA cm−2 and hydrogen evolution reaction with 120 mV overpotential at 10 mA cm−2 in 1 M KOH. Moreover, merely 1.64 V cell voltage is required to drive 10 mA cm−2 current density for overall water splitting. [Display omitted] • Flower-like Ni 3 (NO 3) 2 (OH) 4 /CeO 2 /NF is constructed by a hydrothermal strategy. • The synergistic effect of Ni 3 (NO 3) 2 (OH) 4 and CeO 2 improves the catalytic activity. • Ni 3 (NO 3) 2 (OH) 4 /CeO 2 /NF shows the lowest overpotential for both OER and HER. • Ni 3 (NO 3) 2 (OH) 4 /CeO 2 /NF exhibits excellent overall water splitting performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Engineering lattice strain was successfully realized in NbFe-Ni x Se y catalyst. • Locally unbalanced Coulomb forces trigger lattice distortion and vacancy. • The NbFe-Ni x Se y exhibited distinguished performance for overall water splitting. Engineering lattice strain, especially when it combines with the lattice distortion and vacancy (LDV) induced by locally unbalanced Coulomb forces (LUCFs), can improve the local coordination environment of atoms to achieve synergistically active sites and dynamic regulation of electrocatalysts, which are beneficial to high-performance bifunctional water splitting. Considering that Ni-based selenides possess abundant variable valence states, the Nb/Fe diatomic heterogeneous spin states are purposely introduced to produce LUCFs for improving the electronic coordination environment of the materials. The as-prepared Nb/Fe co-doped Ni-Ses (NbFe-Ni x Se y) electrocatalyst exhibits the prominent oxygen and hydrogen evolution reaction (OER/HER) properties, with low overpotentials of 237 and 226 mV at 50 mA cm−2, respectively. The alkaline water electrolyzer with NbFe-Ni x Se y as both anodic and cathodic electrodes only requires a cell potential of 1.7 V to reach 50 mA cm−2 in a continuous operation of 50 h. This work provides a new insight to regulate the electronic structure of advanced catalyst materials at the atomic level through LUCFs-induced LDV and further push forward the energy conversion technology. [ABSTRACT FROM AUTHOR]

• Mo 3 S 4 /Co 1-x S nanosheets are synthesized by a simple one-step hydrothermal method. • Mo 3 S 4 /Co 1-x S@CF-8 has high hydrophilicity. • The bimetallic sulfide compound has high catalytic activity. • Mo 3 S 4 /Co 1-x S@CF-8 can achieve efficient overall water splitting. Hydrogen generation through electrochemical water decomposition is a promising method to address the global energy crisis. Herein, we report the synthesis of a series of flower-like Mo 3 S 4 /Co 1-x S composites on Co foil (Mo 3 S 4 /Co 1-x S@CF) as high-performance electrochemical water-splitting catalysts in an alkaline environment. The flower-like array structure of Mo 3 S 4 /Co 1-x S@CF not only increases the electrochemically active surface area of ​​the catalyst, but also facilitates the release of bubbles generated, resulting in enhanced catalytic activity. For the hydrogen evolution reaction, the Mo 3 S 4 /Co 1-x S@CF electrode exhibits good stability and excellent catalytic activity in 1.0 M KOH (η 10 = 105 mV), 1.0 M PBS (η 10 = 92 mV) and 0.5 M H 2 SO 4 (η 10 = 68 mV) solutions. For the oxygen evolution reaction, the electrode displays excellent stability and catalytic activity in 1.0 M KOH solution (η 10 = 215 mV). When used for overall water splitting in 1.0 M KOH solution, Mo 3 S 4 /Co 1-x S@CF achieves a current density of 10 mA cm−2 at a low potential of 1.58 V and maintains it stably for 40 h. This study presents a simple method for preparing transition metal-based bimetallic composite catalysts for efficient hydrogen production. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting has proven to be the most promising way to generate hydrogen. However, the high cost and low efficiency of the catalysts for cathode and anode in water splitting device remain the most knotty obstacle that needs to be stepped over. The optimal electrocatalysts can lower the energy costs required for water splitting via the reduced overpotential. Therefore, developing efficient and nonprecious electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) is highly critical and challenging. Cobalt (Co)-based electrocatalysts have been widely applied as electrocatalysts for HER and OER in water splitting. In this review, the mechanisms of HER and OER, was first illustrated, the preparation and electrochemical performance of various Co-based electrocatalysts, including cobalt oxides, hydroxides, sulfides, phosphides, nitrides and selenides for HER or OER are then summarized. Finally, the potential challenges and the future perspective of Co-based electrocatalysts are proposed. Image 1 [ABSTRACT FROM AUTHOR]

Catalytic systems based on nanospheres usually show satisfied catalytic activities due to their huge specific surface areas for active sites immobilization. However, their catalytic activities are usually restricted by the absence of active sites inside the nanospheres and the inadequate communications between the interior and exterior of the nanospheres. Therefore, it can be anticipated that great improvement will be achieved if a porous three-dimensional catalytic system can be designed, through which the activity sites can be distribute interior and exterior. Herein, polydopamine (PDA) NPs with uniform sizes of 300 nm are prepared. Then, the Ru nanoclusters (Ru NCs) are uniformly generated inside and on the surface of the PDA NPs to afford the bi-nanospheres (Ru-PDA NPs). After annealing, the porous carbonized Ru-PDA NPs (Ru-cPDA-750 NPs) with electroactive nitrogen atoms are finally obtained, exhibiting small overpotential (42 mV at the current density of 10 mA cm−2), low value of Tafel slope (35 mV decade−1) and robust stability for hydrogen evolution reaction (HER), which are comparable to that of Pt/C catalyst. Moreover, the study on the effect of Ru NCs amount on electrocatalytic ability reveals that Ru-cPDA NPs loaded with 0.08 wt% of Ru NCs exhibit the best HER catalytic performance compared with the Ru-cPDA NPs loaded with other amount of Ru NCs (0.04–0.16 wt%). Polydopamine nanoparticles (PDA NPs) were obtained by self-polymerization of dopamine and used as the porous framework to load nanoclusters (Ru NCs) either inside or outside for all-around generation of hydrogen. The catalytic system exhibited low overpotential, low value of Tafel slope, robust stability, and low cost for hydrogen evolution reaction, which are comparable to that of Pt/C catalyst. Image 1 • Spherical PDA NPs with controlled sizes from 50 to 500 nm are successfully prepared. • Ru NCs are generated both inside and outside the porous PDA NPs with electroactive N. • Both the size of Ru-cPDA NPs and the loading amount of Ru NCs can be well controlled. • The Ru-cPDA NPs show excellent HER activity and lower cost compared to that of Pt/C. [ABSTRACT FROM AUTHOR]

The development of electrocatalyst with remarkable activity for hydrogen production through water or urea splitting is critical for coping with the energy crisis, but still remains a lot of obstacles. In order to improve the electrocatalytic activity, rational design of nanostructures with rich active sites is an efficient method. Herein, a porous flower-like Mo-doped NiS on Ti mesh (Mo-doped p-NiS/Ti) is synthesized through selective etching of Al(OH) 3 in Mo-doped NiAl layered double hydroxides, and then followed by a facile hydrothermal sulfuration process using sodium sulfide as S source to afford Mo-doped p-NiS/Ti. As a non-noble metal catalyst, Mo-doped p-NiS/Ti catalyst exhibits excellent electrocatalytic performance in electrolyte of 1.0 M KOH or 1.0 M KOH with 0.3 M urea. To drive a current density of 10 mA·cm−2, a small overpotentials of 147.6 mV and 162.3 mV in 1.0 M KOH and 1.0 M KOH with 0.3 M urea are required, respectively, and remarkable durability is observed in 1.0 M KOH or urea water solutions. More significantly, Mo-doped p-NiS/Ti holds promises for potential implementation in the overall water or urea splitting. • Porous flower-like Mo-doped NiS is highly efficient electrocatalyst for overall water splitting. • Obtaining a porous structure by a simple selective etching method • The Mo-doping can enhance the catalytic performance. • Mo-doped p-NiS/Ti is used in a two-electrode system for overall water or urea splitting. [ABSTRACT FROM AUTHOR]

Considering the synergistic effect of transition metal phosphides and 3D structure substrates, herein, we directly deposited well-defined hierarchical radial Ni x P nanospheres on Ni foam via a facile, one-step co-electrochemical method to function as highly active flexible electrodes for both hydrogen evolution reaction and supercapacitor. Impressively, the bifunctional Ni x P/NF electrode requires an overpotential of only 63 mV to achieve a current density of 10 mA cm −2 and demonstrates a low Tafel slop of 55 mV dec −1 in 1 M KOH. Moreover, the electrochemical supercapacitor based on this hierarchical Ni x P/NF electrode also shows a superior specific capacitance of 1684 mF cm −2 (382.7 F/g) at a current density of 2 mA cm −2 and an outstanding retention ratio of 110.9% of its original capacitance value after 4000 cycles in 6 M KOH. Hopefully, excellent electrochemical performances demonstrate that this Ni x P/NF material could be a promising candidate for future applications in both hydrogen evolution reactions and supercapacitors. [ABSTRACT FROM AUTHOR]

Modifying electrocatalysts' structures and regulating their reaction kinetics is essential to improve the performance of electrocatalysts. Here, we report the Fe 3 O 4 /NiFe layered double hydroxides/Fe 3 O 4 (Fe 3 O 4 /NiFe LDH / Fe 3 O 4) with a sandwich structure by a one-step hydrothermal process. The interface synergistic effect between Fe 3 O 4 and NiFe LDH together with abundant electroactive sites encapsulated inside the Fe 3 O 4 oxide layer can stabilize important charge transfer intermediates and promote the reaction kinetics, which could result in remarkable electrochemical performance. As a result, the resulting Fe 3 O 4 /NiFe LDH/Fe 3 O 4 exhibits the lowest overpotential requirements of η 10 = 134 mV and η 50 = 267 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, respectively. A two-electrode electrolyzer assembled with Fe 3 O 4 /NiFe LDH/Fe 3 O 4 as both cathode and anode require a low cell voltage of 1.648 V to achieve the current density response of 10 mA cm−2 toward overall water splitting. Furthermore, the Fe 3 O 4 /NiFe LDH/Fe 3 O 4 also displays excellent industrial catalytic performance by simulating the industrial electrolysis for OER, requiring only 353 mV at the large current density of 1000 mA cm−2. This work puts a deep insight into the role of the confined space of transition metal-based catalysts in electrocatalysis. • Fe 3 O 4 /NiFe LDH/Fe 3 O 4 is fabricated via a one-pot hydrothermal method. • Fe 3 O 4 /NiFe LDH/Fe 3 O 4 shows prominent electrocatalytic properties and good stability. • Fe 3 O 4 /NiFe LDH/Fe 3 O 4 achieves efficient water oxidation at a large current density. [ABSTRACT FROM AUTHOR]

[Display omitted] • Comodification of Molybdate and LDH interlayer carbonate anion. • The construct of atomic-level coupled heterostructure (NFCH-NMO). • The interface engineering with high energy phase boundary effect. • The NFCH-NMO exhibit distinguished performance for overall water splitting. Favorable regulation of electronic coordination environment, especially combined with the interface engineering with synergistic effects to design efficient, stable and low-cost transition-metal-based catalysts for industrial electrocatalytic overall water splitting (EOWS) is a key renewable energy technology, but still facing a daunting challenge. Here, molybdate modification cooperates with LDH interlayer carbonate anion to construct atomic-level coupled heterostructure (NFCH-NMO), and the resulting strong electron interaction at the two-phase interface to directly optimize the electronic structure and d-band center of NiFe-based catalyst. Owing to the high-energy phase boundary effect and the rapid mass transfer advantages of the 3D mesoporous super-hydrophilic surface, the as-prepared NFCH-NMO exhibits remarkable oxygen and hydrogen evolution reaction (OER/HER) catalytic activity, with low overpotentials of 219/203 and 289/297 mV at 50 and 500 mA·cm−2, respectively. The alkaline water electrolyzer of NFCH-NMO || NFCH-NMO only requires a cell potential of 1.66 and 1.839 V to reach 50 and 500 mA·cm−2. This work provides a well-defined catalyst for EOWS at high current density and shows the interfacial engineering of heterostructure with the high-energy interface effect via synergistic modification of LDH interlayer carbonate anion and molybdate is a suitable strategy to enhance the internal electrocatalytic performance of NiFe based catalysts. [ABSTRACT FROM AUTHOR]

• The MoNiFeSx@FeNi3 is prepared as electrocatalyst for overall water splitting in alkaline medium. • The MoNiFeSx@FeNi3 exhibits excellent catalytical activity for overall water splitting. • The electrocatalyst exhibits excellent stability and durability for long term catalysis. [Display omitted] One of the challenges to realize large-scale water splitting is the lack of highly active and low-cost electrocatalysts for its two half reactions: hydrogen and oxygen evolution reactions (HER and OER). In this work, a Mo doping approach is adopted to enhance the HER and OER bifunctionality of NiFe-LDH. The catalyst MoNiFeS x @FeNi 3 obtained after sulfidation exhibits further improved catalytic performance and good stability. In KOH solution (1.0 M), ultralow overpotentials of 67 mV and 142 mV work well to reach current densities of 10 mA cm−2 for HER and OER, separately. In urea (0.33 M) and KOH (1.0 M) solutions, catalyst urea oxidation reaction can be significantly promoted by MoNiFeS x @FeNi 3 , and can reach a current density of 10 mA cm−2 under the condition of 1.31 V. Most importantly, our work elaborates a facile strategy to synthesize novel trimetallic transition metal catalyst as a cut-price substitute for precious metals for highly effective overall water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • The solar renewable resources as additional power for electrocatalysis system. • The efficient transfer/separation of photogenic electron holes. • Excellent electrocatalytical performance for both HER and OER were achieved. By integrating the light-absorbing semiconductor materials into the electrocatalytic network, using the photogenerated-carrier-driven strategy, and thus permitting solar energy to operate as the extra driving force, the efficiency of electrocatalytic water splitting (EWS) is expected to be improved. However, the rational plot of such integrated catalytic system remains an enormous challenge due to the spatial disparity between photocatalytic components and electrocatalytic components. Herein, a MgCo 2 O 4 @WO 3 core–shell heterostructure (MCW CSHS) is constructed by the simple one-step hydrothermal coordination of the spinel oxide MgCo 2 O 4 (as the electron acceptor) and the WO 3 semiconductor (as the electron donor). The cogitatively designed MCW CSHS catalyst can effectively eliminate the spatial disparity between the two above functional components and provide significantly increased surface area and roughness, which can enhance light absorption by restraining diffuse reflection and promoting electron transfer in EWS. Under solar illumination, the electrocatalytic activity of MCW CSHS is significantly improved due to the electronic structure regulation, yielding 50 mA·cm−2 at overpotentials of 243 mV for oxygen evolution reactions and 161 mV for hydrogen evolution reactions in 1 M KOH. The solar energy enhanced electrochemical system based on bifunctional materials has a broad application prospect in the efficient H 2 production by EWS. [ABSTRACT FROM AUTHOR]

• Cu/CuO@Co/Co 3 O 4 samples were synthesized by a simple three-step reaction process. • Cu/CuO@Co/Co 3 O 4 -300 exhibits remarkable HER with low Tafel slopes and durable performances. • This research provides a new method for designing efficient non-precious catalysts for hydrogen evolution reaction. [Display omitted] The hydrogen evolution reaction (HER) is significant to the development of next-generation electrochemical energy devices. The exploration for a non-noble metal catalyst for energy conversion to replace rare and expensive noble metals is fully necessary. Herein, a novel hierarchical Cu and Co-decorated CuO@Co 3 O 4 nanorod-thorns structure is generated on the Cu foam (denoted as Cu/CuO@Co/Co 3 O 4) and utilized as an efficient electrocatalyst for hydrogen evolution reaction (HER) in 1.0 M KOH electrolyte. The Cu/CuO@Co/Co 3 O 4 -300 electrode displays low overpotentials for HER (82 mV) electrocatalytic performance at the current density of 10 mA cm−2 and low Tafel slopes of 48 mV dec-1 are also achieved. Impressively, Cu/CuO@Co/Co 3 O 4 -300 can consecutively generate H 2 with of its initial performance after 35 h in 1.0 M KOH electrolyte. Meanwhile, the electrochemical performance of Cu/CuO@Co/Co 3 O 4 -300 is superior or considerable to most of reported on Cu-based water splitting electrocatalysts. As evidenced, reduction of oxides to metal for electrocatalysts can remarkably raise the catalytic activities for hydrogen evolution reaction. In a word, this work affords a new thought to design efficient non-precious catalysts for hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

• Ti mesh-supported heterostructured CoO/Co 3 O 4 nanowire array is fabricated. • CoO/Co 3 O 4 heterojunctions provide abundant active sites while array architecture enhances stability to boost charge transfer. • Heterostructured CoO/Co 3 O 4 NA/Ti acts as efficient catalyst for HER, demonstrating superior activity and stability. • CoO/Co 3 O 4 NA/Ti also shows high activity and stability for HER in neutral conditions. Heterostructured catalysts CoO/Co 3 O 4 consist of abundant interfaces between CoO and Co 3 O 4 have demonstrated extraordinary electrocatalytic performance toward HER. [Display omitted] Heterostructured CoO/Co 3 O 4 nanowire array on Titanium mesh (CoO/Co 3 O 4 NA/Ti) is fabricated via a facile controllable calcination treatment of the Co 3 O 4 precursor in a reducing atmosphere (H 2 /Ar) and applied as efficient electrocatalyst for hydrogen evolution reaction (HER). This electrode could catalyze the HER in 1.0 M KOH electrolyte with initial overpotential as low as 2.7 mV and need overpotential of 108 mV to approach 10 mA cm−2. Remarkably, it also shows high catalytical activity and long-time durability for HER both in phosphate buffer saline (PBS) and NaCl solution. This work may inspire the design of other high-performance three dimensional-nanostuctured (3D-nanostuctured) HER catalysts with abundant heterojunction interfaces. [ABSTRACT FROM AUTHOR]

Controllably constructing the functional microscopic surfaces, especially via the escape of metal atoms from extremely stable texture to achieve super-hydrophilic interfaces, as efficient bifunctional catalysts for water splitting is a daunting challenge but critical for sustainable economic development. Based on hydrothermal coordination strategy, we take advantage of strong oxidizing property of nitrate ions to realize temperature-controllable atom-escape of metal Ni for self-assembling super-hydrophilic hydroxide FeNi–OH on nickel base as electrocatalysts of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Such distinctive Ni source, resulting in improved ohmic contact and mechanical robustness of catalysts, in conjunction with super-hydrophilicity-accelerated bubble separation and electrolyte contact, endows the catalyst with excellent electrocatalytical activity for both HER and OER in alkaline solution. Super-hydrophilic FeNi–OH delivers the current density of 50 mA cm−2 at overpotentials of 236 mV for OER and 196 mV for HER. Water electrolysis with FeNi–OH as anode and cathode demands a cell voltage of 1.664 V to drive 50 mA cm−2 in 1.0 M KOH, continuously operating for 25 h. This study opens up an avenue in establishing super-hydrophilic structure via self-assembly of the escaped atoms, broadening the horizon on low-cost iron-containing catalyst preparation for energy conversions. • Temperature-controllable atom-escape from metal Ni was realized. • Super-hydrophilic structure facilitates electrolyte/catalyst contact. • Excellent electrocatalytical activities for both HER and OER were achieved. [ABSTRACT FROM AUTHOR]

• Fe-doped Ni 3 S 2 nanorods are synthesized by a simple one-step hydrothermal method. • Application of bimetallic composite foam (FeNi 3) avoid the use of iron salt reagents. • Fe doping significantly improves the catalytic performance of Ni 3 S 2. • Fe-Ni 3 S 2 @FeNi 3 -8 can achieve efficient overall water splitting and urea electrolysis. The development of high-performance and inexpensive bifunctional electrocatalysts to replace precious metal catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains a thorny issue in the field of electrochemical water splitting. Here, a three-dimensional rods array catalysts of Ni 3 S 2 doped with trace amount of Fe on foam FeNi 3 (Fe-Ni 3 S 2 @FeNi 3) are synthesized. It is found experimentally that Fe-Ni 3 S 2 @FeNi 3 has excellent catalytic activity and corrosion resistance in both acidic, neutral and alkaline solutions. In 1.0 M KOH solution, only small overpotentials of 105 mV and 213 mV are required to achieve the current densities of 10 mA cm−2 for HER and OER respectively. In addition, Fe-Ni 3 S 2 @FeNi 3 -8 also exhibits excellent catalytic activity in 0.5 M H 2 SO 4 solution (η 10 = 48 mV) and 1.0 M PBS solution (η 10 = 83 mV) for HER. In 1.0 M KOH and 0.33 M urea solution, Fe-Ni 3 S 2 @FeNi 3 -8 requires only 1.40 V to provide the current density of 10 mA cm−2 for urea oxidation reaction (UOR). As evidenced, doping Fe element into catalyst can significantly increase the catalytic activities for HER and OER. This work demonstrates a new and facile approach to prepare novel bimetallic transition metal catalysts as inexpensive alternatives to precious metal catalysts for efficient hydrogen production. [ABSTRACT FROM AUTHOR]

In this work, we report an electrocatalyst of hierarchical trimetallic sulfide FeCo 2 S 4 –NiCo 2 S 4 supported on Ti mesh (denoted as NiCoFe–S/Ti) for full water splitting in basic media. The NiCoFe–S/Ti shows an efficient and stable electrocatalytic performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). As an OER catalyst, NiCoFe–S/Ti shows a low overpotential of 230 mV at 10 mA cm−2 and a small Tafel slope of ∼65 mV dec−1. As a HER electrocatalyst, it also shows a low potential of −150 mV at 10 mA cm−2, a small Tafel slope of 38 mV dec−1, and a superior durability of maintaining the same catalytical activity for at least 10 h under basic condition. The superior activity and high stability of NiCoFe–S/Ti can be attributed to the highly exposed active sites, excellent charge transfer ability, and good synergistic effect resulted from multi-components. The NiCoFe–S/Ti based overall water splitting exhibits a low onset potential (∼1.47 V), a low splitting potential (∼1.51 V) at 10 mA cm−2 in 1.0 M KOH. This work will pave a way to the development of non-noble-metal, earth-abundant, bifunctional electrocatalyst for overall water splitting under basic conditions. A hierarchical trimetallic sulfide FeCo 2 S 4 –NiCo 2 S 4 /Ti catalyst with excellent catalytic activity for both HER and OER was fabricated by a typical gas sulfidation of hydrothermally obtained NiCoFe LDH/Ti precursor. Image 1 • Hierarchical trimetallic sulfide FeCo 2 S 4 –NiCo 2 S 4 nanosheet arrays supported on a Ti mesh were synthesized successfully. • The optimized catalyst showed excellent performance for HER and OER and superior performance for overall water splitting. • The activity and stability are due to the increased active sites, excellent charge transfer ability, and synergistic effect. [ABSTRACT FROM AUTHOR]