Self-adaptive ZrN coating enables stable acidic oxygen evolution on Co₃O₄ through dynamic surface reconstruction

The development of acid-stable, non-precious catalysts for the oxygen evolution reaction (OER) remains a critical challenge for proton exchange membrane water electrolyzers (PEMWEs). While Co₃O₄ shows promising OER activity, its rapid dissolution in acidic media severely limits practical application. Here, we design a self-adaptive protection strategy by depositing ZrN coatings on Co₃O₄ precursor via magnetron sputtering. Controlled calcination transforms the initial ZrN coating into a mixed-phase Zr₂ON₂ and ZrO₂ surface layer. This unique coating architecture combines the high conductivity of Zr₂ON₂ with the corrosion resistance of ZrO₂, enabling high OER performance with a low overpotential of 362 mV at 10 mA cm^-2 and good stability of over 140 h at 100 mA cm^-2 in 0.1 M HClO₄. Structural characterization reveals that under OER conditions, the coating spontaneously reconstructs, preferentially forming Zr₂ON₂ due to its thermodynamic stability. This reconstruction simultaneously optimizes interfacial charge transfer and suppresses Co over-oxidation, thereby inhibiting dissolution. When integrated into PEMWEs, the catalyst demonstrates practical viability, sustaining 500 mA cm^-2 at 1.8 V with >40 h stability at 200 mA cm^-2. This work establishes dynamic coating reconstruction as a powerful strategy for designing stable acidic OER catalysts.