Molybdenum Doping Activates Lattice Oxygen in Ruthenium Oxide for Efficient Acidic Water Oxidation

Ruthenium dioxide (RuO 2 ) is a highly prospective acidic oxygen evolution reaction (OER) catalyst. However, its limited activity and stability impede the broader application, particularly under stringent acidic conditions. In this work, molybdenum (Mo) doping in the RuO 2 lattice (Mo‐RuO 2 ) was used to enhance the Ru‐O covalency, activate lattice oxygen atoms, and steer the OER process toward the lattice‐oxygen‐mediated mechanism (LOM). Optimization of the OER kinetics was achieved with the extent of LOM participation dictated by the concentration of the Mo dopant. Moreover, experimental results indicate that the Mo dopant also improves proton mobility, ultimately accelerating the OER turnover. Remarkably, the Mo‐RuO 2 catalyst exhibits excellent OER activity, with an overpotential of only 199 mV at 10 mA cm −2 , fast kinetics with a Tafel slope of 53.1 mV dec −1 , mass activity of 1341.9 A gRu −1 at 1.53 V (vs. reversible hydrogen electrode) and is highly stable during continuous operation for 180 h in acidic media. Furthermore, proton exchange membrane water electrolyser performance evaluations demonstrated the Mo‐RuO 2 catalyst achieving a notably low cell voltage of 1.713 V at a current density of 1 A cm −2 . This work demonstrates that doping engineering significantly improves the OER activity of RuO 2 by altering the reaction pathway.