Modulating charge distribution to enhance lattice oxygen reactivity by incorporating tungstate into NiFe₂O₄ spinel for enhanced overall water splitting

Nickel-based spinel catalysts for bifunctional industrial overall water splitting still suffer from critical performance limitations. In this study, WO₄^2- doped NiFe₂O₄ spinel materials with a self-supported structure on Ni foam were synthesized via hydrothermal and calcination processes. The optimized catalyst PW-NiFe₂O₄ exhibits remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance, affording overpotentials of 202 mV (HER) and 248 mV (OER) at 100 mA/cm², corresponding to 1.31-fold and 1.12-fold enhancements relative to the pristine NiFe₂O₄ electrode. Moreover, an activity of 340 mA/cm² at 1.85 V was delivered by the material, and stable operation at 100 mA/cm² for 120 h was maintained in a simulated anion exchange membrane water electrolysis (AEMWE), outperforming most reported catalysts of the same type. Experimental results reveal that the introduction of high-valent W can elevate the valence state of the Ni species, and it is also verified by theoretical calculations that the O 2p band center is upshifted, indicating an enhancement in the covalent nature of Ni-O bonds. These results confirm the triggering of an efficient lattice oxygen mechanism (LOM) during the OER. Furthermore, the adsorption energies of water and the H* intermediate on Ni sites are effectively modulated by the incorporation of W, which facilitates the intrinsic activity in HER. This study presents a promising strategy for the development of bifunctional spinel-based catalysts specifically designed for use in AEMWE systems.