Adaptive Morphing of Hydroxyl Groups on Covalency Competing Spinel Oxides Boosting Oxygen Evolution Reactions

Abstract

Spinel oxides based on first-row transition metals (M_d) have been recognized as cost-effective alternatives to noble metal catalysts in oxygen evolution reactions (OERs), and a multimetal strategy is usually employed to enhance their OER activity. However, it is challenging to rely solely on the combination of these 3d metals to achieve optimal OER activity as their similar metal–oxygen covalency cannot provide sufficient intermodulation to obtain the desirable electronic structure. Here we report that the incorporation of p-block single atoms (M_p, Bi, Sn, and Sb) into octahedral sites of a model spinel oxide NiFe₂O₄ (NFO) can effectively induce asymmetric M_p-O-M_d covalency competition, where the M_p-O covalency acts as an electron reservoir that adaptively modulates the reactivity of M_d sites. This allows surface hydroxyl groups to morph dynamically with each electron transfer step, leading to near-optimal formation energies of the OER intermediates. The subsequent experiments as well as in situ and ex situ characterizations have successfully validated the theoretical predictions, especially since the design of Bi-doped NFO (Bi-NFO) shows significant improvement in specific activity compared to pristine spinel NFO. Our work provides important insights into the design principle of earth-abundant oxide catalysts for the OER by leveraging covalency competition, which may be extended to other catalytic reactions.