Enhanced dual-mechanism oxygen evolution through partial anion filling of oxygen vacancies in spinel oxides

The oxygen evolution reaction (OER) is kinetically limited by the multi-step adsorbate evolution mechanism (AEM) in pure spinel oxides. Although the lattice oxygen-mediated mechanism (LOM) can provide faster kinetics, it usually leads to structural instability due to uncontrolled oxygen loss. Herein, we address this challenge by developing a "oxygen vacancies-anion partial filling" strategy, where S^2- anions are selectively incorporated into oxygen vacancies of Co₃O₄ nanowire arrays (Co₃O₄-V_O-S/NF), which strengthens the interaction with adsorbed intermediates by promoting the formation of high-valent Co⁴⁺ sites to enhance the AEM pathway, and simultaneously activates lattice oxygen under the combined influence of S^2- anions and residual oxygen vacancies, as substantiated by in situ spectroscopy/mass spectrometry and chemical probe. Further theoretical analyses reveal that upward shifts in the Co 3d band centers bolster adsorbate interactions in the AEM, and the upward shifts in O 2p band centers coupled with a reduced energy difference between Co 3d and O 2p band centers, which facilitate lattice‑oxygen oxidation in the LOM. Benefiting from the compatible multi-mechanism design, the Co₃O₄-V_O-S/NF achieves a low overpotential of 301 mV at 50 mA cm^-2 in alkaline media, along with robust stability exceeding 120 h. This strategy is applicable to various spinel oxides (e.g., ZnCo₂O₄, CoCr₂O₄, Fe₃O₄), reducing the OER overpotential by 40-70 mV at 50 mA cm^-2, and provides diverse pathways for designing high-performance electrocatalysts.