Mixed Ionic–Covalent Bonds Achieve Durable Acidic Water Oxidation

The widespread deployment of proton exchange membrane (PEM) water electrolysis is hindered by the instability of oxygen evolution reaction (OER) catalysts under acidic conditions, stemming from coupled degradation mechanisms: lattice oxygen overoxidation (driven by high metal-oxygen (M-O) covalency) and acid-induced metal leaching/collapse. Here, we introduce an electronegativity-guided Li- and Ru-doped spinel Co₃O₄ (LRCO) catalyst featuring mixed Li-O (ionic) and Ru/Co-O (covalent) bonding. This design simultaneously stabilizes lattice oxygen via strong Li-O anchoring and modulates metal valence states through Ru-O-Co electron sharing, preventing overoxidation. Operando studies reveal a potential-dependent mechanism where Ru donates electrons to Co at low potentials, forming active Ru species, and electron redistribution prevents Ru overoxidation at high potentials. Crucially, Li-O bonds effectively suppress oxygen vacancy formation throughout, and Ru-O coordination remains stable, even at high potentials. LRCO achieves a record-low overpotential of 141 mV at 10 mA cm^-2 with >3,300 h stability. Integrated PEM electrolyzers operated >720 h at 1 A cm^-2, achieving a key milestone toward next-decade industry targets.