Oxophilicity-Directed Ru Doping of Co ₃ O ₄ for Stable Acidic Oxygen Evolution Reactions

The development of durable non–iridium catalysts for the acidic oxygen evolution reaction (OER) is crucial for scaling up proton exchange membrane water electrolyzers (PEMWEs) for hydrogen production. However, simultaneously achieving both high activity and stability under harsh acidic conditions remains a key challenge. In this study, we show a Ru-doped Co 3 O 4 catalyst with atomically dispersed Ru sites via a tailored electrodeposition–cation exchange synthesis. The catalyst exhibits an overpotential of 173 mV at 10 mA cm –2 in 0.5 M H 2 SO 4 and maintains stable operation for over 2,623 h at 10 mA cm –2 with a negligible decay rate of 0.011 mV h –1 in a three-electrode cell. Scanning transmission electron microscopy and X-ray absorption spectroscopy reveal that atomically dispersed Ru single atoms selectively replace Co 3+ ions in the octahedral sites of Co 3 O 4 . The combination of in situ Raman, in situ FT-IR spectroscopies, pH-dependence activity, and differential electrochemical mass spectrometry (DEMS) reveals a transition from the lattice oxygen mechanism (LOM) to the oxide path mechanism (OPM) pathway induced by oxophilic Ru doping through weakening the metal–oxygen (MO) covalency and enhancing structural flexibility. Furthermore, the formation of local Ru–O–Co bridging configurations within the octahedral framework further promotes the OPM pathway by enabling strong electronic coupling and optimizing the adsorption and desorption behavior of oxygen intermediates. Our work demonstrates oxophilicity-directed doping coupled with M–O covalency modulation as a general strategy to design durable, high-performance catalysts for the acidic OER and related applications.