Oxygen‐Vacancy–Driven Reactivity in Nanocrystal‐Assembled NiFe ₂ O ₄ Toward Efficient Oxygen Evolution

Developing highly active electrocatalysts for the oxygen evolution reaction is a pivotal challenge in sustainable water electrolysis. Herein, we report a novel in situ oxidative phase‐restructuring strategy to fabricate oxygen vacancy‐rich NiFe 2 O 4 (NFO) directly on nickel foam. Distinct from conventional hydrothermal methods that typically yield thermodynamically stable crystals with limited intrinsic defects, our unique one‐pot process involves the formation of a reduced metallic intermediate. The subsequent drastic phase transformation from this metallic state to a spinel oxide thermodynamically enforces the generation of abundant oxygen vacancies to relieve lattice stress, resulting in unique polycrystalline nanocrystal assemblies (NFO‐1). Electrochemical evaluations reveal that NFO‐1 significantly outperforms its thermodynamically equilibrated counterpart (NFO‐2), exhibiting a low overpotential of 330 mV at 20 mA cm −2 and a remarkable mass activity of 6.78 A g −1 . This superior performance is primarily attributed to intrinsic oxygen vacancies generated during the oxidative phase evolution, which optimize the active‐site electronic structure and enhance charge–transfer kinetics. Furthermore, the catalyst demonstrates excellent durability over 1200 cycles. This work highlights oxidative phase restructuring as a powerful pathway to engineer intrinsic defects for high‐efficiency energy‐conversion applications.

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