Heterointerface Engineering of FeOOH@Ni₃N Electrocatalysts for Industrially Compatible Alkaline Water Electrolysis

The rational design of earth-abundant electrocatalysts is pivotal for advancing alkaline water electrolysis toward sustainable hydrogen production. Here, we report a hierarchical FeOOH@Ni₃N heterostructure comprising a redox-active iron oxyhydroxide overlayer conformally coupled with a conductive trinickel nitride core directly grown on nickel foam. This hybrid catalyst drives the oxygen evolution reaction (OER) with ultralow overpotentials of 209, 245, and 284 mV at 10, 100, and 500 mA cm^-2, respectively, while maintaining exceptional stability under industrial-level operations. Integrated into a two-electrode electrolyzer, FeOOH@Ni₃N achieves current densities of 10, 500, and 1000 mA cm^-2 at cell voltages of only 1.49, 1.72, and 1.78 V, outperforming noble-metal-based benchmarks. Operando/in-situ spectroscopies, combined with electrokinetic and isotope-effect analyses, reveal that enhanced intrinsic activity originates from reconstructed proton-electron transfer pathways at the Fe-Ni heterointerface. Strong interfacial coupling stabilizes high-valent Ni⁴⁺ = O/,Fe⁴⁺ = O species and promotes an unconventional dual-site hydroxyl nucleophilic attack mechanism, wherein OH^- attack on Fe⁴⁺ = O forms a bridging *OOH intermediate as the O─O bond-forming step, synergistically assisted by adjacent Ni centers. These findings delineate a clear structure-activity-stability relationship for Fe-Ni heterostructures and showcase heterointerface engineering of conductive nitrides with oxyhydroxides as a scalable strategy for developing durable, high-rate OER electrocatalysts.