Catalysts For Water Electrolysis Research Articles

MXene-based Materials for Water Splitting: Synthesis and Modification.

With abundant metal site and tunable electronic structure, MXene is considered as a promising electrocatalyst for the conversion of energy molecules. In this review, the latest research progress on inexpensive MXene-based catalysts for water electrolysis is summarized. Typical preparation and modification methods and their advantages and disadvantages are briefly discussed, with a focus on the regulation and design of the surface interface electronic states, which improve the electrocatalytic performance of MXene-based materials. The main strategies for the electronic state modification include end-group modification, heteroatom doping, and heterostructure construction. Some limitations of MXene-based materials, which should be considered in the rational design of advanced MXene-based electrocatalyst, are also discussed. Finally, prospects for the rational design of Mxene-based electrocatalysts is proposed.

Transition metal single atoms anchoring VTe2 for efficient overall water splitting and oxygen reduction reactions: A first principles study

Cost-effective and high surface free energy are the advantages of single atom catalysts (SAC), but higher surface free energy produces nanoclusters and reduced catalytic activity. Herein, through the calculation based on first principles, transition metals (TM) anchored in VTe2 electrolytic water catalysts have been designed. Te atom with strong electronegativity and TM atom with catalytic activity form strong covalent bond, which makes TM atom have better catalytic activity and stability. The calculation results show that Cr@VTe2 and Fe@VTe2 have good catalytic activity for HER with overpotential is 0.180 V and 0.176 V, respectively, which is about 60% lower than the original VTe2. Ni@VTe2 has excellent catalytic performance for OER with an overpotential of 0.34 V, which is about 60% lower than the original VTe2. Fe@VTe2 and Ni@VTe2 showed significant catalytic activity to ORR, superior to the benchmark catalyst Pt. Notably, Fe@VTe2 is considered to be an effective electrocatalyst for HER and ORR, while Ni@VTe2 is considered to be an effective electrocatalyst for OER and ORR. Excitingly, Fe@VTe2 is expected to be a three-functional catalyst for HER, OER and ORR under certain conditions. This work provides theoretical support for the practical application of cost-effective VTe2 based catalysts for water electrolysis.

Amorphous co-modified catalyst based on interfacial coupling effect for efficient hydrogen production by water electrolysis

Development of synthesis procedures of efficient amorphous heteroatom coupling interfaces is important for the improvement of electrocatalyst performance. Herein, the Co/Ni NWs/NF composite electrode was prepared using magnetic effect, where Ni nanowires were initially grown on Ni foam to increase its specific surface area, followed by the electrodeposition of amorphous cobalt nanosheets to form multiple active sites for the hydrogen evolution reaction (HER). The electrochemical results show that the prepared Co/Ni NWs/NF can deliver a current density of 10 mA cm−2 at an overpotential of 49 mV in 1 M KOH electrolyte. The physical test results demonstrate that the introduction of cobalt species onto Ni nanowire result in the interface coupling effect, which can efficiently increase the HER active surface sites and modify the interface charge distribution. The study provides new approach for design and preparation of highly active hydrogen evolution catalysts for water electrolysis.

Novel hierarchical FeWO4–FeNi3 heterostructure nanosheets for highly active water electrolysis at large current density

The development of efficient bifunctional catalysts for water electrolysis is of great significance, especially at large current density. Herein, a kind of heterostructure catalyst composed of FeNi3 nanoparticles and FeWO4 nanosheets is prepared by hydrothermal and calcination. It exhibits good activity for both oxygen evolution reaction and hydrogen evolution reaction , only 1.43 V and −43 mV are needed to obtain ±10 mA cm−2 respectively. Besides, it can work for 100 h at 1000 mA cm−2 under simulated industrial condition (6.0 M KOH solution, 60 °C) for overall water splitting , showing robust stability. This good performance could owe to: (1) Heterostructure facilitates the electrons transfer at the interface, thereby promoting the reaction process and enhancing the intrinsic catalytic activity; (2) Hierarchical array structure consisting of nanoparticles and nanosheet can expose more active areas and accelerate the transport of ions and charges, accelerating the release of bubbles for enhancing stability. Therefore, this work offers a promising method to design high-performance catalyst for practical water electrolysis.

Trace Lattice S Inserted RuO2 Flexible Nanosheets for Efficient and Long-Term Acidic Oxygen Evolution Catalysis.

Pursuing highly active and long-term stable ruthenium (Ru) based oxygen evolution reaction (OER) catalyst for water electrolysis under acidic conditions is of great significance yet a tremendous challenge to date. To solve the problem of serious Ru corrosion in an acid medium, the trace lattice sulfur (S) inserted RuO2 catalyst is prepared. The optimized catalyst (Ru/S NSs-400) has shown a record stability of 600 h for the solely containing Ru (iridium-free) nanomaterials. In the practical proton exchange membrane device, the Ru/S NSs-400 can even sustain more than 300 h without obvious decay at the high current density of 250mA cm-2 . The detailed investigations reveal that S doping not only changes the electronic structure of Ru via forming RuS coordination for high adsorption of reaction intermediates but also stabilizes Ru from over-oxidation. This strategy is also effective for improving the stability of commercial Ru/C and homemade Ru-based nanoparticles. This work offers a highly effective strategy to design high-performance OER catalysts for water splitting and beyond.

Catalytic manipulation of Ni nanostructures-immobilized CNTs via nitrogen coupling for robust water electrolysis and effective glucose detection

The development of a novel multifunctional high-performance electrocatalyst is a critical requirement for electrochemical applications. This study reports an effective engineering approach to enhance multi-integrated active sites of nickel (Ni) catalysts through the coupling of nitrogen (N) atoms to trigger surface-functionalized Ni nanoparticles that are well dispersed over a structure of carbon nanotubes (CNTs). Excitingly, the N-doped Ni@CNTs material possesses good catalytic features with a required overpotential (η) of ∼133.8 mV to achieve 50 mA/cm2 toward hydrogen evolution reaction and ∼330 mV to achieve 100 mA/cm2 toward oxygen evolution reaction in 1.0 M KOH. To assess overall water splitting practicability, an electrolyzer device derived from the N-doped Ni@CNTs(+,−) is fabricated and shows an operation voltage of only ∼1.62 V at 10 mA/cm2 together with a prospective stability that is superior to Pt/C(−)//RuO2(+). Furthermore, the non-enzymatic glucose sensor derived from the N-doped Ni@CNTs electrode displays high sensitivity of 5.2 μA/mM/cm2, wide linear range of (0.01–3.7) mM, low detection limit of ∼17.4 μM (S/N = 3), excellent selectivity, and long-term stability. Our study suggests that the developed N-doped Ni@CNTs are favorable catalyst for practical water electrolysis to produce green hydrogen and for non-enzymatic glucose sensor application.

(Digital Presentation) The Effects of Sulfur-Oxygen Ratio at the Heterogeneous Interface on Oxygen Evolution Reaction Performance of Ni3S2@Ni3Fe Catalysts for Alkaline Water Electrolysis

Alkaline water electrolysis is the important pathway for the green hydrogen generation, where oxygen evolution reaction (OER) kinetics is limited due to the sluggish proton-coupled electron transfer in the four-electron reaction. It’s very important for the design of high-performance OER catalysts in order to improve its kinetics performance. Here, porous heterogeneous Ni3S2@Ni3Fe catalysts are prepared on nickel mesh (NM) by the electrodeposition process. Oxygen atoms are introduced into Ni3S2 by the vulcanization processes, and different S-O atom ratios are adjusted by varying vulcanization temperature. The influence of S-O ratio at heterogeneous interface on OER performance of Ni3S2@Ni3Fe is systematacially investigated. The results indicate that high S-O ratio improves the OER performance of Ni3S2-xOx@Ni3Fe, which is attributed to H2O adsorption ability enhancement on Ni3Fe surface due to the formation of unique heterogeneous electronic structure by density functional theory (DFT) calculation analysis. The prepared NM/Ni3S2-xOx@Ni3Fe (vulcanization temperature at 300 oC) electrode exhibits the improved OER performance in 30 wt% KOH solutions at high current density up to 1000 mA cm-2. It provides the guidance for the design of high-performance Ni3S2-based heterogeneous catalysts by introducing oxygen atom and increasing the sulfur-oxygen ratio.

Facile Construction of Three-Dimensional Heterostructured CuCo2S4 Bifunctional Catalyst for Alkaline Water Electrolysis

Developing an efficient multi-functional electrocatalyst with high efficiency and low cost to replace noble metals is significantly crucial for the industrial water electrolysis process and for producing sustainable green hydrogen (H2) fuel. Herein, ultrathin CuCo2S4 nanosheets assembled into highly open three-dimensional (3D) nanospheres of CuCo2S4 (Cu/Co = 33:67) were prepared by a facile one-pot solvothermal approach and utilized as a bifunctional electrocatalyst for efficient overall water splitting. The as-prepared CuCo2S4 is characterized structurally and morphologically; the BET surface area of the CuCo2S4 (Cu/Co = 33:67) catalyst was found to have a larger specific surface area (21.783 m2g−1) than that of other catalysts with a Cu/Co ratio of 67:33, 50:50, and 20:80. Benefiting from a highly open structure and ultrathin nanosheets with excellent exposure to catalytically active sites, CuCo2S4 (Cu/Co = 33:67) is identified as an efficient catalyst for the proton reduction and oxygen evolution reactions in 1 M KOH with an overpotential of 182 and 274 mV at 10 mA cm−2, respectively. As expected, a low cell voltage of 1.68 V delivers a current density of 10 mA cm−2. Stability and durability are also greatly enhanced under harsh alkaline conditions. Therefore, this work provides a simple strategy for the rational design of spinel-based transition metal sulfide catalysts for electrocatalysis.

Multiscale Hierarchical Structured NiCoP Enabling Ampere‐Level Water Splitting for Multi‐Scenarios Green Energy‐to‐Hydrogen Systems

AbstractEfficient and stable low‐cost catalysts are seriously lacking for industrial water electrolysis at large‐current‐density. To meet industrial‐scale hydrogen production, fully utilized active sites by a rational structure design is an attractive route. Herein, dynamic microstructure manipulation of bimetallic phosphide NiCoP is conducted. Among different microstructures for NiCoP, as‐obtained NiCoP‐120 at hydrothermal temperature of 120 °C, shows a special multiscale hierarchical structure from 3D‐nickel foam substrates, 2D‐nanosheets to 1D‐nanoneedles, which is conducive to efficient utilization of active sites and rapid gas release, thus manifesting outstanding electrocatalytic activities and stability as required by industry. To reach a current density of 10 and 1000 mA cm−2 for the hydrogen evolution reaction (HER), NiCoP‐120 requires ultra‐low overpotentials of 56 and 247 mV, respectively. Particularly, as a bifunctional catalyst, it only needs 1.981 V to drive the 1 A cm−2 overall water splitting and can maintain stable output for 600 h, which is superior to almost all reported non‐noble metal catalysts. Moreover, its application prospect in integrated green energy‐to‐hydrogen systems, including sunlight, wind, thermal, and lithium cells, is well demonstrated. This work provides a guiding strategy for the design of industrial water electrolysis catalysts and the establishment of an externally driven water‐splitting hydrogen production system.

Highly Efficient Spatial Three-Level CoP@ZIF-8/pNF Based on Modified Porous NF as Dual Functional Electrocatalyst for Water Splitting.

The development of non-noble metal catalysts for water electrolysis to product hydrogen meets the current strategic need for carbon peaking and carbon neutrality. However, complex preparation methods, low catalytic activity and high energy consumption still limit the application of these materials. Herein, in this work we prepared a three-level structured electrocatalyst of CoP@ZIF-8 growing on modified porous nickel foam (pNF) via the natural growing and phosphating process. In contrast to the common NF, the modified NF constructs a large number of micron-sized pores carrying the nanoscaled catalytic CoP@ZIF-8 on the millimeter-sized skeleton of bare NF, which significantly increases the specific surface area and catalyst load of the material. Thanks to the unique spatial three-level porous structure, electrochemical tests showed a low overpotential of 77 mV at 10 mA cm-2 for HER, and 226 mV at 10 mA cm-2 and 331 mV at 50 mA cm-2 for OER. The result obtained from testing the electrode's overall water splitting performance is also satisfactory, needing only 1.57 V at 10 mA cm-2. Additionally, this electrocatalyst showed great stability for more than 55 h when a 10 mA cm-2 constant current was applied to it. Based on the above characteristics, the present work demonstrates the promising application of this material to the electrolysis of water for the production of hydrogen and oxygen.

Interface engineering and heterometal doping Co–Mo/FeS for oxygen evolution reaction

The sluggish kinetics of the oxygen evolution reaction (OER) limits the development of water electrolysis technology and the long-term efficiency of hydrogen energy production. In addition, it is important to evaluate the reconstruction performance of OER catalysts for actual water electrolysis. We created a self-supported electrode with FeS film coated Fe foam as a substrate, ordered resoluble molybdate (MoO42−) anions in interlayers, and Co-doped as a catalytically active phase for the OER. The catalyst is capable of electrochemical self-reconstruction (ECSR). With the dissolution of molybdate and sulfur ions, the catalyst surface cobalt iron oxide (CoFe2O4) forms an active amorphous FeCoOOH, which is favorable for alkaline OER. We realized the introduction of new active sites in the catalyst reconstruction process. Finally, the composite CoFeOx catalyst increased the specific surface area, promoted bubble transport, and enhanced electron mass transfer. The synergistic coupling effect of the catalyst makes it have excellent OER activity and stability. Remarkably, Co–Mo/FeS nanosheets afforded an electrocatalytic OER with a current density of 100 mA cm−2 at a low overpotential of 321 mV. These discoveries open up new opportunities for the application of doping and template-directed surface reconfiguration, which holds promise as an effective electrocatalyst for the OER.

Perspectives on current and future iridium demand and iridium oxide catalysts for PEM water electrolysis

Proton exchange membrane water electrolysis (PEMWE) is projected to become a key technology to enable the decarbonisation of ‘hard to abate’ sectors of the economy. However, the technology’s reliance on iridium, one of the scarcest elements on Earth, as an oxygen evolution reaction catalyst, has led to uncertainty over whether a large-scale PEMWE industry can be realised. This work investigates the future iridium demand of the global PEMWE sector and examines how different catalyst strategies can improve iridium utilisation in the anode catalyst. Iridium utilisation targets necessary to avoid a situation where the PEMWE sector becomes limited by iridium supply are reviewed. Modelling the iridium demand of the PEMWE sector shows that iridium utilisation needs to improve by an order of magnitude by 2050 to avoid iridium supply limiting the capacity expansion. Furthermore, implementing closed-loop iridium recycling by 2035 would increase the installed capacity in 2050 by ∼2.7x compared to a scenario with no iridium recycling. If these two conditions are met, global PEMWE capacity could reach 1.3 TW by 2050 using only 20% of annual global primary iridium supply, which we consider to be realistic given future demand projections. Different types of iridium-based anode catalysts are compared in terms of iridium utilisation using membrane electrode assembly (MEA) testing data from the literature, with the order found to be supported nanoparticles ≈ extended surface structures > mixed oxides > nanoparticles. The need to place greater research focus on catalyst stability and the ability to make homogeneous catalyst layers at low iridium loadings is discussed. As a main result, it is found that a terrawatt-scale PEMWE industry can avoid being constrained by iridium supply if technological development of a similar level to that seen in PEM fuel cells and high iridium recycling rates are realised.

Regulating electronic states of nitride/hydroxide to accelerate kinetics for oxygen evolution at large current density

Rational design efficient transition metal-based electrocatalysts for oxygen evolution reaction (OER) is critical for water splitting. However, industrial water-alkali electrolysis requires large current densities at low overpotentials, always limited by intrinsic activity. Herein, we report hierarchical bimetal nitride/hydroxide (NiMoN/NiFe LDH) array as model catalyst, regulating the electronic states and tracking the relationship of structure-activity. As-activated NiMoN/NiFe LDH exhibits the industrially required current density of 1000 mA cm−2 at overpotential of 266 mV with 250 h stability for OER. Especially, in-situ electrochemical spectroscopic reveals that heterointerface facilitates dynamic structure evolution to optimize electronic structure. Operando electrochemical impedance spectroscopy implies accelerated OER kinetics and intermediate evolution due to fast charge transport. The OER mechanism is revealed by the combination of theoretical and experimental studies, indicating as-activated NiMoN/NiFe LDH follows lattice oxygen oxidation mechanism with accelerated kinetics. This work paves an avenue to develop efficient catalysts for industrial water electrolysis via tuning electronic states.

NiFe Alloy Integrated with Amorphous/Crystalline NiFe Oxide as an Electrocatalyst for Alkaline Hydrogen and Oxygen Evolution Reactions.

The rational design of efficient and low-cost electrocatalysts based on earth-abundant materials is imperative for large-scale production of hydrogen by water electrolysis. Here we present a strategy to prepare highly active catalyst materials through modifying the crystallinity of the surface/interface of strongly coupled transition metal-metal oxides. We have thermally activated the catalysts to construct amorphous/crystalline Ni-Fe oxide interfaced with a conductive Ni-Fe alloy and systematically investigated their electrocatalytic performance toward the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline solution. It was found that the Ni-Fe/oxide material with a crystalline surface oxide phase showed remarkably superior HER activity in comparison with its amorphous or poorly crystalline counterpart. In contrast, interestingly, the amorphous/poorly crystalline oxide significantly facilitated the OER activity in comparison with the more crystalline counterpart. On one hand, the higher HER activity can be ascribed to a favorable platform for water dissociation and H-H bond formation, enabled by the unique crystalline metal/oxide structure. On the other hand, the enhanced OER catalysis on the amorphous Ni-Fe oxide surfaces can be attributed to the facile activation to form the active oxyhydroxides under OER conditions. Both are explained based on density functional theory calculations. These results thus shed light onto the role of crystallinity in the HER and OER catalysis on heterostructured Ni-Fe/oxide catalysts and provide guidance for the design of new catalysts for efficient water electrolysis.

Ultra‐Fast In Situ Reconstructed Nickel (Oxy)Hydroxide Nanoparticle Crosslinked Structure for Super‐Efficient Alkaline Water Electrolysis by Sacrificing Template Strategy

The rapid construction of water electrolysis catalysts by a sacrificing template in an electrochemical environment is rarely a concern. Herein, using a fluorine‐rich (F‐rich) nickel fluoride (NiF2) grown on nickel foam (NF) as a sacrificial template, a highly effective alkaline catalyst is designed. In terms of in situ reassembling, the NiF2 template can be transformed into nickel hydroxide (Ni(OH)2) in hydrogen evolution reaction (HER) and nickel oxyhydroxide (NiOOH) in oxygen evolution reaction (OER), respectively, after only 100 CV cycles, on account of the rapid ion exchange of F− and OH− in an electrochemical environment. Due to the presence of nanocatalytic units, abundant lattice defects, and porous large specific surface structures caused by the reconstruction, it only takes low overpotentials of 57 mV for HER and 228 mV for OER (@10 mA cm−2), with outstanding stability up to 15 d (@100 mA cm−2). Consequently, only a low cell voltage of 1.53 V (@10 mA cm−2) is needed for overall water splitting, superior to commercial noble metal catalysts as benchmarks. Meanwhile, it can output stable current densities of 10, 100, and 500 mA cm−2 approaching 10 d under constant cell voltages of 1.55, 2.0, and 2.5 V, respectively.

Doping of Cr to Regulate the Valence State of Cu and Co Contributes to Efficient Water Splitting.

Water electrolysis in alkaline media is the most promising technology for hydrogen production, but efficient electrocatalysts are required to reduce the overpotential in HER and OER processes. In this work, the multicomponent transition metal catalyst Cr-Cu/CoOx was loaded on copper foam by electrodeposition and annealing, and the catalyst exhibited excellent electrochemical activity. The HER overpotential is 21 mV and the OER overpotential is 252 mV at a current density of 10 mA cm-2. The overall water splitting voltage is 1.51 V, even better than the Pt/C//RuO2 two-electrode system (1.61 V). The excellent performance of this catalyst is mainly derived from the close synergistic interaction among Cu, Co, and Cr. The doping of Cr modulates the valence states of Cu and Co at the active sites and improves the adsorption of various reaction intermediates. Density functional theory (DFT) calculations show that the doping of Cr can optimize the adsorption of the reaction intermediate H*. Meanwhile, the high-valent Cr and Co promote hydrolysis through strong adsorption with OH-. The present work provides a reasonable strategy for designing low-cost transition metals as efficient catalysts for water electrolysis.

Surpassing Pt hydrogen production from {200} facet-riched polyhedral Rh2P nanoparticles by one-step synthesis

The efficient water electrolysis catalyst is prominently important and urgent to forward the widespread applications of hydrogen energy. In this work, polyhedral-morphology controlled rhodium phosphide (Rh2P) nanoparticles are synthesized by one-step high temperature pyrolysis under Ar atmosphere at 90 Pa. By analyzing the morphologies of Rh2P, the crystal facets of {200}, {220} and {111} are dominant in the 26-facet polyhedrons, and {200} facets account for 58% of the total surface area of polyhedral 26-facet shapes. The overpotentials of polyhedral Rh2P NPs are 12.6 mV and 10.5 mV at 10 mA m−2 in 0.5 M H2SO4 and 1 M KOH electrolytes, even lower than those of Pt/C. Theoretical calculations indicate that {200} facets of Rh2P NPs have the highest catalytic activity among {200}, {111}, and {220}, with the lowest hydrogen adsorption free energy. The substantial exposure of {200} facets is beneficial to the high catalytic activity of Rh2P NPs.

Preparation of Cu/Sn-Organic Nano-Composite Catalysts for Potential Use in Hydrogen Evolution Reaction and Electrochemical Characterization.

In this work, the solvothermal solidification method has been used to be prepared as a homogenous CuSn-organic nano-composite (CuSn-OC) to use as a catalyst for alkaline water electrolysis for cost-effective H2 generation. FT-IR, XRD, and SEM techniques were used to characterize the CuSn-OC which confirmed the formation of CuSn-OC with a terephthalic acid linker as well as Cu-OC and Sn-OC. The electrochemical investigation of CuSn-OC onto a glassy carbon electrode (GCE) was evaluated using the cyclic voltammetry (CV) method in 0.1 M KOH at room temperature. The thermal stability was examined using TGA methods, and the Cu-OC recorded a 91.4% weight loss after 800 °C whereas the Sn-OC and CuSn-OC recorded 16.5 and 62.4%, respectively. The results of the electroactive surface area (ECSA) were 0.5, 0.42, and 0.33 m2 g-1 for the CuSn-OC, Cu-OC, and Sn-OC, respectively, and the onset potentials for HER were -420, -900, and -430 mV vs. the RHE for the Cu-OC, Sn-OC, and CuSn-OC, respectively. LSV was used to evaluate the electrode kinetics, and the Tafel slope for the bimetallic catalyst CuSn-OC was 190 mV dec-1, which was less than for both the monometallic catalysts, Cu-OC and Sn-OC, while the overpotential was -0.7 vs. the RHE at a current density of -10 mA cm-2.

Crystal Facet and Electronic Structure Modulation of Perovskite Oxides for Water Oxidation

In water-splitting catalysts, exposing high-activity crystal facets with optimal electronic structures can significantly enhance the oxygen evolution reaction (OER) kinetics. In this work, we demonstrate a facile strategy for simultaneously modulating the preferential crystal facet and electronic structure of perovskite oxides for their use as water-electrolysis catalysts using a template-mediated growth approach. Experimental and computational analyses revealed that the preferred crystal facet of La0.5Sr0.5CoO3 (LSC) grown on MoReS2 was effectively modulated to the (110) plane, and the free energy barrier of the rate-determining step was lowered by such crystal facet engineering. Furthermore, the interfacial charge transfer between LSC and MoReS2 enabled the optimal electronic structure of the B-site cation in LSC. Consequently, LSC grown on MoReS2 exhibited an OER activity of 210 mV at 10 mA cm–2, surpassing the performance of state-of-the-art perovskite oxide-based catalysts. Our findings provide new insights into the design of efficient perovskite oxide-based electrocatalysts for water electrolysis.

Phase Evolution on the Hydrogen Adsorption Kinetics of NiFe-Based Heterogeneous Catalysts for Efficient Water Electrolysis.

Transition metal layered double hydroxides, especially nickel-iron layered double hydroxide (NiFe-LDH)shows significant advancement as efficient oxygen evolution reaction (OER) electrocatalyst but also plays a momentous role as a precursor for NiFe-based hydrogen evolution reaction (HER) catalysts. Herein, a simple strategy for developing Ni-Fe-derivative electrocatalysts via phase evolution of NiFe-LDH under controllable annealing temperatures in an argon atmosphere is reported. The optimized catalyst annealed at 340 o C (denoted NiO/FeNi3 ) exhibits superior HER properties with an ultralow overpotential of 16 mV@10mA cm-2 . Density functional theory simulation and in situ Raman analyses reveal that the excellent HER properties of the NiO/FeNi3 can be attributed to the strong electronic interaction at the interface of the metallic FeNi3 and semiconducting NiO, which optimizes the H2 Oand Hadsorption energies for efficient HER and OER catalytic processes. This work will provide rational insights into the subsequent development of related HER electrocatalysts and other corresponding compounds via LDH-based precursors.