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Combining interfacial oxygen vacancy engineering with a built-in electric field (BEF) technique is an efficient way to build efficient and practical electrocatalytic water-splitting catalysts. In this study, a Fe 3 O 4 -FeSe 2 heterojunction catalyst with oxygen vacancies supported on reduced graphene oxide (rGO) was designed and successfully fabricated using a simple two-step hydrothermal method. Owing to the different Fermi levels of Fe 3 O 4 and FeSe 2 , a BEF was generated at the interface, which enhanced the separation of negative and positive charges, thus optimizing the adsorption of hydrogen/oxygen intermediates on the heterostructures and improving the activity of the catalyst. Experimental results show that Fe 3 O 4 -FeSe 2 /rGO/NF exhibits excellent hydrogen and oxygen evolution performances, with low overpotentials of 234/300 mV at 100 mA⋅cm -2 . A water electrolyzer assembled with Fe 3 O 4 -FeSe 2 /rGO/NF as both the anode and cathode requires only a small potential of 1.78 V to reach a current density of 100 mA⋅cm -1 . This study provides an innovative approach for constructing a catalyst with excellent electrocatalytic performance for overall water splitting., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)