Rapid Synthesis of Various Electrocatalysts on Ni Foam Using a Universal and Facile Induction Heating Method for Efficient Water Splitting

Electrocatalytic water splitting for the production of hydrogen proves to be effective and available. In general, the thermal radiation synthesis usually involves a slow heating and cooling process. Here, a high-frequency induction heating (IH) is employed to rapidly prepare various self-supported electrocatalysts grown on Ni foam (NF) in liquid- and gas-phase within 1–3 min. The NF not only serves as an in situ heating medium, but also as a growth substrate. The as-synthesized Ni nanoparticles anchored on MoO₂ nanowires supported on NF (Ni-MoO₂/NF-IH) enable catalysis of hydrogen evolution reaction (HER), showing a low overpotential of −39 mV (10 mA cm⁻²) and maintaining the stability of 12 h in alkaline condition. Moreover, the NiFe layered double hydroxide (NiFe LDH/NF-IH) is also synthesized via IH and affords outstanding oxygen evolution reaction (OER) activity with an overpotential of 246 mV (10 mA cm⁻²). The Ni-MoO₂/NF-IH and NiFe LDH/NF-IH are assembled to construct a two-electrode system, where a small cell voltage of ≈1.50 V enables a current density of 10 mA cm⁻². More importantly, this IH method is also available to rapidly synthesize other freestanding electrocatalysts on NF, such as transition metal hydroxides and metal nitrides.     

Porous Pd/NiFeOx Nanosheets Enhance the pH-Universal Overall Water Splitting

Modulating the morphology and chemical composition is an efficient strategy to enhance the catalytic activity for water splitting, since it is still a great challenge to develop a bifunctional catalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) over a wide pH range. Herein, Pd/NiFeO_x nanosheets are synthesized with tightly arranged petal nanosheets and uniform mesoporous structure on nickel foam (NF). The porous 2D structure yields a larger surface area and exposes more active sites, facilitating water splitting at all pH values. The overpotential of Pd/NiFeO_x nanosheets for OER is only 180, 169, and 310 mV in 1 m KOH, 0.5 m H₂SO₄, and 1 m phosphate-buffered saline (PBS) conditions at 10 mA cm⁻² current density, as well as excellent HER activity with ultralow overpotential in a wide pH range. When using porous Pd/NiFeO_x nanosheets as bifunctional catalysts for water splitting, it just required a cell voltage of 1.57 V to reach a current density of 20 mA cm⁻² with nearly 100% faradic efficiency in alkaline conditions, which is much lower than that of benchmark Pt/CǁRuO₂ (1.76 V) couples, along with the improving stability benefiting from the good corrosion resistance of the inner NiFeO_x nanosheets.     

Engineering Active Iron Sites on Nanoporous Bimetal Phosphide/Nitride Heterostructure Array Enabling Robust Overall Water Splitting

Alkaline water electrolysis is a commercially viable technology for green H₂ production using renewable electricity from intermittent solar or wind energy, but very few non-noble bifunctional catalysts simultaneously exhibit superb catalytic efficiency and stability at large current densities for hydrogen and oxygen evolution reactions (HER and OER, respectively), especially for iron-based catalysts. Given that iron is the most abundant and least expensive transition metal, iron-based compounds are very attractive low-cost targets as active electrocatalysts for bifunctional water splitting with large-current durability. Herein, the in situ construction of a self-supported Fe₂P/Co₂N porous heterostructure arrays possessing superb bifunctional catalytic activity in base is reported, featured by low overpotentials of 131 and 283 mV to attain a current density of 500 mA cm⁻² for HER and OER, respectively, outperforming most of non-noble bifunctional electrocatalysts reported hitherto. Particularly, this hybrid catalyst also displays an excellent overall water splitting activity, requiring low voltages of 1.561 and 1.663 V to attain 100 and 500 mA cm⁻² with excellent durability in 1 m KOH, respectively. Most importantly, the catalyst is stable for >120 h, even when the current density is 500 mA cm⁻², which is prominently superior to IrO₂⁽⁺⁾//Pt⁽⁻⁾ coupled noble electrodes, and is among the very best bifunctional catalysts reported thus far. Detailed theoretical calculations reveal that the interfacial interaction between Fe₂P and Co₂N can further improve the H* binding energy at the iron sites.     

Bimetal-Incorporated Black Phosphorene with Surface Electron Deficiency for Efficient Anti-Reconstruction Water Electrolysis

Surface reconstruction (SRC) is a common phenomenon and a promotion manner for Ni/Co-based precatalysts during the water splitting process. However, the catalytic surface reconstruction will in turn complicate the streamlined prediction and modeling on the catalytic activity. Hence, the rational design of anti-SRC catalysts is highly desirable, but challengeable. In this article, a series of affordable bimetal-incorporated black phosphorene (BP) catalysts are constructed by an in situ electro-exfoliation/insertion method for anti-SRC water electrolysis. It is found that the bimetals (e.g., NiFe, NiPd) are of cationic and covalent incorporation with electron-deficient state in few-layer BP. The optimized bimetal-BP structures present excellent and stable catalytic performances with low overpotentials in hydrogen evolution (HER, 53 mV, NiPd-BP) and oxygen evolution (OER, 268 mV, NiFe-BP) reactions at 10 mA cm⁻² in 1 m KOH. The anti-SRC behaviors are elucidated by in situ Raman studies during HER/OER, probably due to the balanced electron transfer pathway on Ni sites. This research opens interesting possibilities for designing the anti-SRC catalysts for efficient hydrogen production and authentic structure-activity understandings.     

Regulating the Band Structure of Ni Active Sites in Few-Layered Nife-LDH by In Situ Adsorbed Borate for Ampere-Level Oxygen Evolution

Realizing rapid transformation of hydroxide to high-active oxyhydroxide species in layered double hydroxide (LDH) catalyst plays a significant role in enhancing its activity toward oxygen evolution reaction (OER) for hydrogen production from water. Here, a scalable strategy is developed to synthesize defect-rich few-layered NiFe-LDH nanosheets (f-NiFe-LDH-B) with in situ borate modified for boosted and stable OER due to that the borate can narrow the bandgap for Ni sites to realize a more conductive electronic structure. Besides, the adsorbed borate can tune the d band center of Ni sites to promote of hydroxide transformation and facilitate the adsorption of the OER intermediates. The f-NiFe-LDH-B catalyst, therefore, requires only 209 and 249 mV overpotential to deliver 10 and 100 mA cm⁻² OER, respectively, with a Tafel slope of 43.5 mV dec⁻¹. Moreover, only 1.8 V cell voltage is required to reach Ampere-level overall water splitting for 500 h at room temperature.     

Mo-/Co-N-C Hybrid Nanosheets Oriented on Hierarchical Nanoporous Cu as Versatile Electrocatalysts for Efficient Water Splitting

Designing robust and cost-effective electrocatalysts based on Earth-abundant elements is crucial for large-scale hydrogen production through electrochemical water splitting. Here, nitrogen-doped carbon engrafted Mo₂N/CoN hybrid nanosheets that are seamlessly oriented on hierarchical nanoporous Cu scaffold (Mo-/Co-N-C/Cu), as highly efficient electrocatalysts for alkaline hydrogen evolution reaction are reported. The constituent heterostructured Mo₂N/CoN nanosheets work as bifunctional electroactive sites for both water dissociation and adsorption/desorption of hydrogen intermediates while the nitrogen-doped carbon bridges electron transfers between electroactive sites and interconnective Cu current collectors by making use of Mo-/Co-N-C bonds and intimate C/Cu contacts at interfaces. As a consequence of unique architecture having electroactive sites to be sufficiently accessible, self-supported nanoporous Mo-/Co-N-C/Cu hybrid electrodes exhibit outstanding electrocatalysis in 1 m KOH, with a negligible onset overpotential and a low Tafel slope of 47 mV dec⁻¹. They only take overpotential of as low as 230 mV to reach current density of 1000 mA cm⁻². When coupled with their electro-oxidized derivatives that mediate efficiently the oxygen evolution reaction, the alkaline water electrolyzer can achieve ≈100 mA cm⁻² at 1.622 V in 1 m KOH electrolyte, ≈0.343 V lower than the device constructed with commercially available Pt/C and Ir/C nanocatalysts immobilized on nanoporous Cu electrodes.     

Bifunctional Heterostructure Assembly of NiFe LDH Nanosheets on NiCoP Nanowires for Highly Efficient and Stable Overall Water Splitting

3D hierarchical heterostructure NiFe LDH@NiCoP/NF electrodes are prepared successfully on nickel foam with special interface engineering and synergistic effects. This research finds that the as‐prepared NiFe LDH@NiCoP/NF electrodes have a more sophisticated inner structure and intensive interface than a simple physical mixture. The NiFe LDH@NiCoP/NF electrodes require an overpotential as low as 120 and 220 mV to deliver 10 mA cm^?2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 m KOH, respectively. Tafel and electrochemical impedance spectroscopy further reveal a favorable kinetic during electrolysis. Specifically, the NiFe LDH@NiCoP/NF electrodes are simultaneously used as cathode and anode for overall water splitting, which requires a cell voltage of 1.57 V at 10 mA cm^?2. Furthermore, the synergistic effect of the heterostructure improves the structural stability and promotes the generation of active phases during HER and OER, resulting in excellent stability over 100 h of continuous operation. Moreover, the strategy and interface engineering of the introduced heterostructure can also be used to prepare other bifunctional and cost‐efficient electrocatalysts for various applications.     

Active Motif Change of Ni-Fe Spinel Oxide by Ir Doping for Highly Durable and Facile Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is crucial for producing sustainable energy carriers. Herein, Ir (5 mol.%) doped inverse-spinel NiFe₂O₄ (Ir-NFO) nanoparticles deposited on Ni foam (NF) by scalable solution casting are considered a promising OER electrocatalyst for industrial deployments. The Ir-NFO/NF (with minimal lattice distortion by uniform Ir doping) provides an OER overpotential of 251 mV (intrinsically outperforming NFO/NF and benchmarking IrO₂/NF) and extraordinary robustness over 130 days at 100 mA cm⁻². In situ X-ray absorption spectroscopy reveals oxidation only for Fe on NFO, whereas concurrent generation of higher-valent Ni and Fe occurs on Ir-NFO during OER. Density functional theory calculations further demonstrate that Ir substitutes the sublayer Ni octahedral site and switches the main active reaction center from Fe_Oh Fe_Td bridge site (Fe O Fe) on NFO to Ni_Oh–Fe_Td bridge site (Ni O Fe active motif) on Ir-NFO for a co-catalytic OER. This study sheds new light on precious-metal doped Ni-Fe oxides, which may be applicable to other binary/ternary oxide electrocatalysts.     

An Overall Reaction Integrated with Highly Selective Oxidation of 5-Hydroxymethylfurfural and Efficient Hydrogen Evolution

Thermodynamically favorable electrooxidation reactions of biomass derivatives integrated with hydrogen evolution reaction (HER) can simultaneously provide value-added chemicals and hydrogen, and eventually meeting the need for clean and sustainable energy development. Herein, the integration of a six-electron involved anodic half-reaction-selective electrooxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid (FDCA) on a hierarchically layered double hydroxide (CoFe@NiFe) with a cathodic HER in a two-chamber system is reported. The overall reaction reaches 38 mA cm⁻² at 1.40 V and exhibits 100% selectivity to yield FDCA and a nearly 100% Faraday efficiency with hydrogen production of 901 µmol cm⁻². Several operando techniques confirm that the trivalent nickel species in the CoFe@NiFe catalyst are mainly responsible for this 100%-selective oxidation reaction. This integrated overall reaction is thus a new strategy to utilize cheap catalysts and biomass derivatives to simultaneously produce value-added chemicals and sustainable energy materials, and eventually to solve current challenges of energy depletion and environmental pollution.     

Ni3N–CeO2 Heterostructure Bifunctional Catalysts for Electrochemical Water Splitting

Developing low-cost and high-efficient bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is greatly significant for water electrolysis. Here, Ni₃N-CeO₂/NF heterostructure is synthesized on the nickel foam, and it exhibits excellent HER and OER performance. As a result, the water electrolyzer based on Ni₃N-CeO₂/NF bifunctional catalyst only needs 1.515 V@10 mA cm⁻², significantly better than that of Pt/C||IrO₂ catalysts. In situ characterizations unveil that CeO₂ plays completely different roles in HER and OER processes. In situ infrared spectroscopy and density functional theory calculations indicate that the introduction of CeO₂ can optimizes the structure of interface water, and the synergistic effect of Ni₃N and CeO₂ improve the HER activity significantly, while the in situ Raman spectra reveal that CeO₂ accelerates the reconstruction of O_V (oxygen vacancy)-rich NiOOH for boosting OER. This study clearly unlocks the different catalytic mechanisms of CeO₂ for boosting the HER and OER activity of Ni₃N for water splitting, which provides the useful guidance for designing the high-performance bifunctional catalysts for water splitting.     

A CoN-based OER Electrocatalyst Capable in Neutral Medium: Atomic Layer Deposition as Rational Strategy for Fabrication

Reported herein is an active and durable CoN-containing oxygen evolution reaction (OER) electrocatalyst which efficiently functions in a neutral medium (pH ≈7). The composite material (N, S)-RGO@CoN is synthesized by delicate atomic layer deposition (ALD) of CoN on a nitrogen and sulfur (N, S) co-doped reduced graphene oxide (RGO) substrate. Representative results of the comprehensive study are: 1) The flower-like sphere RGO substrate prepared by spray drying method features rich physical and chemical properties, which are beneficial for rapid mass/charge transfer to improve the intrinsic OER process; 2) the optimal ALD material for OER tests is afforded by tuning spray conditions and ALD parameters. Versatile structural and compositional characterizations confirm uniform growth and strong chemical coupling of nanostructured CoN on (N, S)-RGO matrix; 3) the material is electrocatalytically active and durable in a neutral electrolyte, recording an OER overpotential of 220 mV at a current density of 10 mA cm⁻² and stability of 20 h continuous catalysis at 20 mA cm⁻² with nearly 100% Faradic efficiency; 4) Upon the experimental studies and density functional theory calculations, the eventual mechanism of remarkable OER activity conforms to the structural fate of ALD CoN electronic coupling to the carbon substrate.     

Yolk-Shell Structured Zinc-Cobalt-Ruthenium Alloy Oxide Assembled with Ultra-Small Nanoparticles: A Superior Cascade Catalyst toward Oxygen Evolution Reaction

Structure engineering has proven to be an effective strategy for improving the catalytic performance and reducing the cost of ruthenium oxide-based catalysts toward oxygen evolution reactions (OER). Herein, a polyhedron-shaped yolk-shell structure composed of zinc-cobalt-ruthenium ternary metal alloy oxide (ZnCo-RuO₂/C) is prepared, by taking advantage of the Kirkendall effect. The yolk-shell frame and the ensembled metal oxide nanoparticles are 116.9 ± 25.9 nm and 3.1 ± 0.7 nm in diameter, respectively. The porous yolk-shell structure of ZnCo-RuO₂/C exposes abundant active sites and facilitates mass transfer for OER. Theoretical calculations indicate that ZnCo-RuO₂ may break the linear scaling relationship for the OER intermediates and dramatically reduces the energy barrier of the potential determining step, which may be one of the factors that are responsible for the enhanced OER performance of ZnCo-RuO₂/C. In 1 m KOH aqueous electrolyte, ZnCo-RuO₂/C delivers an overpotential of only 180 mV at 10 mA cm⁻² and a Tafel slope of 63 mV dec⁻¹, superior to that of single metal-doped, pristine and commercial RuO₂. As an anode catalyst of zinc-air batteries, ZnCo-RuO₂/C exhibits improved power density and durability relative to commercial RuO₂, very promising for practical application.     

Mechanochemical Post-Synthesis of Metal–Organic Framework-Based Pre-Electrocatalysts with Surface Fe?O?Ni/Co Bonding for Highly Efficient Oxygen Evolution

Rational surface engineering of metal–organic frameworks (MOFs) provide potential opportunities to address the sluggish kinetics of oxygen evolution reaction (OER). However, the development of MOF-based materials with low overpotentials remains a great challenge. Herein, a post-synthesis strategy to prepare highly efficient MOF-based pre-electrocatalysts via all-solid-phase mechanochemistry is demonstrated. The surface of a Fe-based MOF (MIL-53) can be reconstructed and anchored with atomically dispersed Ni/Co sites. As expected, the optimized M-NiA-CoN exhibits a very low overpotential of 180 mV at 10 mA cm⁻² and a small Tafel slope of 41 mV dec⁻¹ in 1 m KOH electrolyte. The superior electrocatalytic OER activity is mainly due to the formation of surface Fe O Ni/Co bonding. Furthermore, density functional theory calculations reveal that the transformation from ^*OH to ^*O is the rate-determining step and the electrocatalytic OER activity trend at different metal sites is Co > Ni≈Fe.     

Assembling Amorphous Metal–Organic Frameworks onto Heteroatom-Doped Carbon Spheres for Remarkable Bifunctional Oxygen Electrocatalysis

Multifunctional electrocatalysts play an increasingly crucial role in various practical electrochemical energy conversion devices. Especially, on the air cathode of rechargeable zinc–air batteries (ZABs), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), requiring efficient bifunctional electrocatalysts, are switched during discharging and charging process. Here, supported by the theoretical computations, a facile strategy for the in situ assembly of NiFe-MOFs nanosheets on heteroatoms-doped porous activated carbon spheres is developed. The newly designed electrocatalyst (NP-ACSs@NiFe-MOFs) shows excellent performance toward bifunctional oxygen electrocatalysis. Specifically, a remarkable low value of potential gap (ΔE = 0.61 V), which is the difference between the potential to reach an OER current density of 10 mA cm⁻² and ORR half-wave potential, is achieved in 0.1 m KOH. Notably, the aqueous ZAB based on NP-ACSs@NiFe-MOFs shows super cycle stability with small voltage gap of only 0.79 V when cycled for 450 h at 10 mA cm⁻². Also, the quasi-solid-state ZAB indicates excellent flexibility and cycling stability. This study presents a facile strategy for the rational integration of different catalytically active components, and can be extended to prepare other strongly competitive multifunctional electrocatalysts.     

Metal Single-Site Molecular Complex–MXene Heteroelectrocatalysts Interspersed Graphene Nanonetwork for Efficient Dual-Task of Water Splitting and Metal–Air Batteries

Development of multifunctional electrocatalysts with high efficiency and stability is of great interest in recent energy conversion technologies. Herein, a novel heteroelectrocatalyst of molecular iron complex (Fe_MC)-carbide MXene (Mo₂TiC₂T_x) uniformly embedded in a 3D graphene-based hierarchical network (GrH) is rationally designed. The coexistence of Fe_MC and MXene with their unique interactions triggers optimum electronic properties, rich multiple active sites, and favorite free adsorption energy for excellent trifunctional catalytic activities. Meanwhile, the highly porous GrH effectively promotes a multichannel architecture for charge transfer and gas/ion diffusion to improve stability. Therefore, the Fe_MC–MXene/GrH results in superb performances towards oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in alkaline medium. The practical tests indicate that Zn/Al–air batteries derived from Fe_MC–MXene/GrH cathodic electrodes produce high power densities of 165.6 and 172.7 mW cm⁻², respectively. Impressively, the liquid-state Zn–air battery delivers excellent cycling stability of over 1100 h. In addition, the alkaline water electrolyzer induces a low cell voltage of 1.55 V at 10 mA cm⁻² and 1.86 V at 0.4 A cm⁻² in 30 wt.% KOH at 80 °C, surpassing recent reports. The achievements suggest an exciting multifunctional electrocatalyst for electrochemical energy applications.     

Ag Anchored Atomically Around Nanopores of Porous Co(OH)2 for Efficient Bifunctional Oxygen Catalysis

Various clean energy storage and conversion systems highly depend on rational design of efficient electrocatalysts for oxygen reactions. Increasing both gas molecular diffusion and intrinsic activity is critical to boosting its efficiency for bifunctional oxygen electrocatalysis. However, controllable synthesis of catalysts that combines gas molecular diffusion and intrinsic activity remains a fundamental challenge. Herein, a two-step synthetic strategy is adopted to fabricate a composite oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional catalyst (P-Ag-Co(OH)₂), of which, atomic Ag is anchored in reactive oxygen atoms around nanopores of Co(OH)₂ nanosheets. Abundant nanopores provide enough gas molecular diffusion channels, and the special Ag-O-Co-OH catalytic groups around nanopores display high intrinsic catalytic activity, which jointly result in an excellent ORR/OER performance. In alkaline electrolyte, P-Ag-Co(OH)₂ displays a high half-wave potential (0.902 V versus RHE) for ORR, and a low overpotential (235 mV at 10 mA cm⁻²) for OER, which is superior to non-noble catalysts in previous studies and Pt/C (Ir/C) catalyst. At the same time, the single-cell zinc-air battery is prepared with an extremely high discharge peak power density of 435 mW cm⁻² and excellent discharge–charge cycle stability.     

Layer-by-Layer Assembly-Based Electrocatalytic Fibril Electrodes Enabling Extremely Low Overpotentials and Stable Operation at 1 A cm−2 in Water-Splitting Reaction

For the practical use of water electrolyzers using non-noble metal catalysts, it is crucial to minimize the overpotentials for the hydrogen and oxygen evolution reactions. Here, cotton-based, highly porous electrocatalytic electrodes are introduced with extremely low overpotentials and fast reaction kinetics using metal nanoparticle assembly-driven electroplating. Hydrophobic metal nanoparticles are layer-by-layer assembled with small-molecule linkers onto cotton fibrils to form the conductive seeds for effective electroplating of non-noble metal electrocatalysts. This approach converts insulating cottons to highly electrocatalytic textiles while maintaining their intrinsic 3D porous structure with extremely large surface area without metal agglomerations. To prepare hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrodes, Ni is first electroplated onto the conductive cotton textile (HER electrode), and NiFe is subsequently electroplated onto the Ni–electroplated textile (OER electrode). The resulting HER and OER electrodes exhibit remarkably low overpotentials of 12 mV at 10 mA cm⁻² and 214 mV at 50 mA cm⁻², respectively. The two-electrode water electrolyzer exhibits a current density of 10 mA cm⁻² at a low cell voltage of 1.39 V. Additionally, the operational stability of the device is well maintained even at an extremely high current density of 1 A cm⁻² for at least 100 h.     

Self-Reconstruction of Sulfate-Containing High Entropy Sulfide for Exceptionally High-Performance Oxygen Evolution Reaction Electrocatalyst

Novel earth-abundant metal sulfate-containing high entropy sulfides, FeNiCoCrXS₂ (where X = Mn, Cu, Zn, or Al), are synthesized via a two-step solvothermal method. It is shown that sulfate-containing FeNiCoCrMnS₂ exhibits superior oxygen evolution reaction (OER) activity with an exceptionally low overpotential of 199, 246, 285, and 308 mV at current densities of 10, 100, 500, and 1000 mA cm^–2, respectively, and surpassing its unary-, binary-, ternary-, and quaternary-metal counterparts. The electrocatalyst yields exceptional stability after 12 000 cycles and 55 h of durability even at a high current density of 500 mA cm^–2. Various in situ and ex situ analyses are used to investigate the self-reconstruction of the sulfides during the OER for the first time. The resulting metal (oxy)hydroxide is believed to be the true active center for OER. The remaining sulfate also contributes to the catalytic activity. Density function theory calculation is in good agreement with the experimental result. The extraordinary OER performance of the high entropy sulfide brings a great opportunity for desirable catalyst design for practical applications.     

Interfacial Engineering of Nickel Hydroxide on Cobalt Phosphide for Alkaline Water Electrocatalysis

Catalysts based on earth-abundant non-noble metals are interesting candidates for alkaline water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overpotential and sluggish kinetics in both the hydrogen and oxygen evolution reactions (HER and OER). In this study, a hybrid catalyst made of iron-doped cobalt phosphide (Fe-CoP) nanowire arrays and Ni(OH)₂ nanosheets is introduced that displays strong electronic interactions at the interface, which significantly improves the interfacial reactivity of reactants and/or intermediates with the hybrid catalyst surface. The combined experimental and theoretical study further confirms that the hybrid catalyst promotes the sluggish rate-limiting steps in both the HER and OER. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.52 V to reach the current density of 10 mA cm⁻² along with superior durability and high conversion efficiency.     

Fabrication of Polyoxometalate Anchored Zinc Cobalt Sulfide Nanowires as a Remarkable Bifunctional Electrocatalyst for Overall Water Splitting

The advancement of a naturally rich and effective bifunctional substance for hydrogen and oxygen evolution reaction is crucial to enhance hydrogen fuel production efficiency via the electrolysis process. Herein, facile and scalable hydrothermal synthesis of bifunctional electrocatalyst of polyoxometalate anchored zinc cobalt sulfide nanowire on Ni-foam (NF) for overall water splitting is reported for the first time. The electrochemical analysis of POM@ZnCoS/NF displays significantly low HER and OER overpotentials of 170/337 and 200/300 mV to attain a current density of 10/40 and 20/50 mA cm⁻², respectively, demonstrating the notable performance of POM@ZnCoS/NF toward H₂ and O₂ evolution reaction in alkaline medium. Additionally, the electrolyzer consisting of the POM@ZnCoS/NF anode and cathode shows an appealing potential of 1.56 V to deliver 10 mA cm⁻² current density for overall water splitting. The high electrocatalytic activity of the POM@ZnCoS/NF is attributed to modulation of the electronic and chemical properties, increment of the electroactive sites and electrochemically active surface area of the zinc cobalt sulfide nanowires due to the anchorage of polyoxometalate nanoparticles. These results demonstrate the advantage of the polyoxometalate incorporation strategy for the design of cost-effective and highly competent bifunctional catalysts for complete water splitting.