Grain Boundary Oxygen Improving the Acidic Oxygen Evolution Reaction of Zn-RuO2@ZnO.

The lattice oxygen evolution reaction (OER) is the currently predominant mechanism, while the grain boundary (GB) OER is still the enigma. This study proposes the grain boundary oxygen mechanism (GBOM) and validates it using Zn-RuO2@ZnO in OER. An optimal GB density in Zn-RuO2@ZnO achieves an overpotential of 170 mV and 600 h durability at 10 mA cm-2. As an anode catalyst in proton-exchange membrane water electrolyzers (PEMWEs), Zn-RuO2@ZnO exhibits exceptional stability (>300 h at 500 mA cm-2) and high efficiency, requiring only 1.68 V to deliver 1 A cm-2 under 60 °C. Notably, the reduced symmetry at GBs enhances the Ru 4dxy-O 2p hybridization, manifested as a distinct antiferromagnetic state, which activates the GBOM pathway and stabilizes its operation through electron transfer into lower-energy orbitals. Our findings highlight that GBs with antiferromagnetic characteristics offer an intriguing design strategy for developing highly active and stable OER catalysts.