Tuning Ru–O Coordination for Switching Redox Centers in Acidic Oxygen Evolution Electrocatalysis

Avoiding lattice oxygen involvement (oxygen redox) while promoting the coupling of adjacent adsorbed oxygen (metal redox) during the acidic oxygen evolution reaction (OER) is essential for gaining high activity and robust stability in RuO₂-based catalysts but remains elusive. Here, we present a precise strategy to selectively activate the metal redox process while suppressing the undesired oxygen redox pathway by fine-tuning the Ru-O coordination number in amorphous RuO_x. The optimized catalyst exhibits outstanding acidic OER performance, achieving a low overpotential of 215 mV at 10 mA cm^-2 and maintaining stability for 300 h with a negligible degradation rate of 100 µV h^-1. X-ray absorption measurements and multiple operando spectra reveal that only Ru₂-O₁₁ moieties can selectively activate the metal redox process, whereas Ru₂-O₉ and Ru₂-O₈ moieties either trigger both redox pathways or bypass them. Theoretical calculations reveal that Ru₂-O₁₁ moiety reduces crystal field splitting energy at active Ru sites, disables lattice oxygen activation, and lowers the energy barrier for oxygen coupling. The strategy developed in this work offers new avenues for switching redox centers and refining OER mechanisms to enhance catalytic performance and long-term stability.