Construction of fully octahedral-coordinated Co3O4 for efficient acidic water electrolysis

• • Tri-Co3O4 achieves 10 mA cm-2 at an overpotential of 269 mV in acidic OER, 181 mV lower than C-Co3O4 (450 mV), directly reducing the voltage penalty that dominates PEMWE stack efficiency and operational cost. • • The fully octahedral [CoO6] framework eliminates tetrahedral Co dissolution, enabling 2500 h of continuous operation at 1.7 V in a practical PEMWE device; this durability threshold exceeds typical non-noble oxide lifetimes by at least an order of magnitude and approaches Ir/Ru benchmarks. • • In situ Co K-edge XAFS shows only a slight Co oxidation-state increase and nearly unchanged Co-O coordination during OER, confirming that the octahedral framework resists reconstruction under anodic potential; this mechanistic stability is essential for mitigating the rapid degradation observed in conventional spinel oxides. • • DFT calculations place the Tri-Co3O4 (10-10) facet closest to the volcano apex with balanced *OH and *O adsorption, while C-Co3O4 Co sites deviate from the optimal activity region; this provides a rational descriptor for designing fully octahedral transition-metal oxides and reducing reliance on noble-metal catalysts.