Tuning the Co pre-oxidation process of Co3O4via geometrically reconstructed F–Co–O active sites for boosting acidic water oxidation†

Cobalt-based oxides are potential alternatives to noble metal catalysts for the acidic oxygen evolution reaction (OER); however, their activity and stability are limited by the surface reorganization of cobalt oxide into the Co(IV)O active phase of pure Co₃O₄ with retarded OER kinetics. Herein, we report a geometrically reconstructed active site F–Co–O of Co₃O_4−xF_x phase by forming an F electron-dominated sharing effect, which prominently regulates the Co pre-OER feature of the pure Co₃O₄ catalyst, and displays an unconventional electrochemical behavior for remarkably boosted acidic water oxidation. The Co₃O_4−xF_x catalyst exhibits a relatively low overpotential of 349 mV at 10 mA cm⁻² and operation durability of 120 h at 100 mA cm⁻² for the acidic OER, making it one of the best-performing non-noble metal catalysts. The in-depth mechanistic analysis via quasi in situ/operando techniques and density functional theory proves the ability of F to adjust the Co pre-oxidation reaction on Co₃O_4−xF_x and reproduces the remarkable activity of the OER over Co₃O_4−xF_x, as well as detailing the switchable rate-determining step and catalytic mechanisms for exceptionally enhanced performance. This work opens feasible avenues for designing acidic OER catalysts of non-precious metal oxides toward commercial water electrolysis.