Metal defects and ruthenium single-atom cooperative catalysis for efficient acidic oxygen evolution reaction.

The synergistic interplay between metal defects and single-atom catalysts offers a promising strategy to enhance electrocatalytic performance for the oxygen evolution reaction (OER) under acidic conditions by modulating the electronic structure and coordination environment of active sites. However, the cooperative mechanisms underlying this synergy remain poorly understood due to the high formation energy of metal defects and the corrosive nature of acidic and oxidative environments. In this study, a defect-engineered catalyst comprising single-atom Ru anchored on Mn-deficient MnO (denoted as Ru-MnO) was synthesized and investigated for acidic OER. The presence of Mn defects was found to reduce electron occupancy in the antibonding orbitals of the Ru active site and shift its d-band center away from the Fermi level. This electronic modulation weakens the interaction between Ru and the O-O* intermediate, thereby facilitating its desorption. In situ Fourier-transform infrared (FT-IR) spectroscopy and density functional theory (DFT) calculations reveal that Ru-MnO follows a favorable the oxide path mechanism (OPM) with a reduced energy barrier, enabling the adsorption and transformation of reaction intermediates at lower overpotentials. As a result, Ru-MnO achieves a low overpotential of 143 mV at a current density of 10 mA cm and demonstrates excellent operational stability over 300 h in 0.5 M HSO. This work underscores the critical role of cooperative effects between metal defects and single atoms in the rational design of efficient and durable OER catalysts for acidic media.