Octahedral Ru Centers Modulate Lattice Covalency and Interfacial PCET for Stable Acidic Oxygen Evolution.

Developing active and durable catalysts for acidic oxygen evolution reaction (OER) is critical for proton-exchange membrane water electrolysis (PEMWE). However, it remains challenging because highly active oxides often undergo over-oxidation and structural degradation under anodic conditions. In this study, we report a Ru-modified CoMn spinel catalyst in which highly oxyphilic Ru is anchored at octahedral sites to regulate both the lattice electronic structure and the interfacial reaction environment. The strong Ru-O covalency and pronounced oxygen-hole character enhance the OER kinetics. Meanwhile, the highly polarized Ru centers reconstruct the interfacial hydrogen-bond network and accelerate interfacial proton-coupled electron transfer (PCET). The introduction of Ru can maintain structural stability during OER through restraining excessive Co oxidation and local coordination changes. As a result, Ru-MnCo2Ox catalyst exhibits an overpotential of 203 mV at 10 mA cm-2 with over 500 h stability in acid. The Ru-MnCo2Ox||Pt/C PEMWE device shows a cell voltage of 1.68 V@1.0 A cm-2, which is much lower than that of commercial RuO2||Pt/C PEMWE device (2.1 V@ 1 A cm-2). Moreover, the Ru-MnCo2Ox||Pt/C can be operated steadily at 0.5 A cm-2 over 300 h.