Fluorine Engineering Induces Phase Transformation in NiCo ₂ O ₄ for Enhanced Active Motifs Formation in Oxygen Evolution Reaction

Abstract Dynamic reconstruction of catalysts is key to active site formation in alkaline oxygen evolution reaction (OER), but precise control over this process remains challenging. Herein, F‐doped NiCo ₂ O ₄ (NiCo ₂ O ₄ ‐F _n ), consisting of a NiCo ₂ O ₄ core and a (NH ₄ )Ni _x Co _1−x F ₃ shell is reported, which promotes the formation of a dual‐metal NiCoOOH active phase. In situ Raman and X‐ray absorption fine structure analyses reveal that the NiCoOOH, rich in oxygen vacancies (O _v ), forms at 1.2 V versus the reversible hydrogen electrode (RHE) for NiCo ₂ O ₄ ‐F ₁ , in contrast to the NiOOH phase formation at 1.4 V versus RHE for undoped NiCo ₂ O ₄ . This is facilitated by the transformation of (NH ₄ )Ni _x Co _1−x F ₃ into amorphous Ni _x Co _1−x (OH) ₂ in the KOH electrolyte without bias. Electrochemical tests show that NiCo ₂ O ₄ ‐F ₁ exhibits a 14‐fold increase in intrinsic activity compared to NiCo ₂ O ₄ . Theoretical calculations suggest that O _v ‐induced unsaturated Co and Ni sites enhance electroactivity by promoting ^* OH intermediates adsorption and conversion, lowering the OER energy barrier. The oriented control of NiCoOOH active motifs in NiCo ₂ O ₄ spinel, achieved through fluorine engineering, paves a new avenue for designing efficient OER electrocatalysts.