Mo-Doping Emergence in FeOOH/NiS_xHeterostructure for Ultrastable Alkaline Overall Water Electrolysis

Developing efficient bifunctional electrocatalysts that synergistically enhance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance remains challenging for advanced electrochemical water splitting. A “lattice doping-interface coupling” strategy is proposed to achieve simultaneous intraphase and interfacial regulation in FeOOH/NiS_x heterostructures by doping molybdenum in nickel sulfide. Mo doping induces electron rearrangement within NiS_x and modulates the electronic states of both Fe and Ni sites via valence electron effects, optimizing intermediate adsorption to enhance HER/OER activity. It also strengthens metal–sulfur bonding and optimizes interfacial charge transfer, significantly improving the long-term stability. This dual-regulation effect creates optimized active centers with modulated d-band structures, as confirmed by density functional theory (DFT) calculations. The resulting FeOOH/Mo-NiS_x catalyst demonstrates great electrocatalytic performance in 1 M KOH, with low overpotentials of 162 mV for HER and 239 mV for OER at 100 mA cm^–2, while maintaining stability over 200 h. When applied in an anion-exchange membrane water electrolysis (AEMWE) cell, it delivers an ultralow voltage of 1.65 V at 1 A cm^–2 with 1200-h durability. This work elucidates the synergistic multimetal regulation mechanism in heterostructures, guiding the design of nonprecious bifunctional electrocatalysts.