MoO₂-Mediated Ni─Fe Bond Contraction and Electronic Modulation in Ni₃Fe Alloy for Efficient Water Electrolysis at High-Current-Densities.

Abstract

Ni₃Fe alloy electrocatalysts show promising activity for water electrolysis but are limited by sluggish hydrogen/oxygen evolution reaction (HER/OER) kinetics, and inefficient gas-liquid mass transfer under high-current-densities. Here, a superhydrophilic/superaerophobic 3D carbonized wood-loaded Ni₃Fe-MoO₂ (Ni₃Fe/MoO₂/CW) heterojunction is designed to address these challenges. X-ray absorption fine structure (XAFS) and theoretical calculations reveal that the introduction of MoO₂ shortens the Ni─Fe bond length, induces electron transfer from Ni₃Fe to MoO₂, and regulates the d-band center of Ni/Fe. These optimized Ni─Fe bonds and electronic structure enhance H─OH bond dissociation and H* adsorption/desorption, thereby accelerating the HER Volmer-Heyrovsky step. Simultaneously, for the OER adsorption evolution mechanism on Ni₃Fe (1.462 eV), the strengthened Ni─O─Mo bond on Ni₃Fe-MoO₂ heterojunction reduces the energy barrier (1.092 eV) of the rate-determining step, significantly improving catalytic efficiency. Thus, Ni₃Fe/MoO₂/CW displays good activity (HER: η_-10/-750 = 45/342 mV; OER: η_300/1000 = 251/306 mV). Notably, the large specific area of Ni₃Fe/MoO₂/CW from its nanosheet-particle structure enhances the electrolyte/bubble exchange at the gas-liquid-solid three-phase interface, enabling stable operation at 1000 mA cm^-2 for 24 h in an anion exchange membrane electrolyzer. This work demonstrates a MoO₂-driven strategy for electronic modulation and metal bond regulation to boost HER/OER kinetics, advancing Ni₃Fe-based catalysts toward practical high-current-densities water electrolysis.