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

## TL;DR

A new FeOOH@Ni3N electrocatalyst improves hydrogen production efficiency and stability in alkaline water electrolysis.

## Contribution

A hierarchical FeOOH@Ni3N heterostructure is engineered to enable high-rate and stable oxygen evolution reaction (OER) under industrial conditions.

## Key findings

- FeOOH@Ni3N achieves ultralow overpotentials of 209, 245, and 284 mV at 10, 100, and 500 mA cm−2 for OER.
- The catalyst maintains exceptional stability during industrial-level operations.
- Operando spectroscopy reveals a dual-site hydroxyl nucleophilic attack mechanism at the Fe–Ni heterointerface.

## Abstract

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.

A hierarchically structured FeOOH@Ni3N electrocatalyst supported on Ni foam enables high‐rate alkaline water electrolysis with industrial‐level stability. Operando spectroscopy reveals that the Fe–Ni heterointerface stabilizes high‐valent Ni4+ = O/Fe4+ = O species and promotes a hydroxyl nucleophilic attack (HNA) mechanism, wherein OH− attack on electrophilic Fe4+ = O forms a bridging Fe3+–OOH⋅⋅⋅O–Ni3+/4+ intermediate, facilitating efficient O─O bond formation and rapid OER kinetics.