Na Substitution Steering RuO₆ Unit in Ruthenium Pyrochlores for Enhanced Oxygen Evolution in Acid

Abstract Although Ruthenium‐based pyrochlore oxides can function as promising catalysts for acidic water oxidation, their limitations in terms of stability and activity still need to be addressed for further application in practical conditions. In this work, the possibility to enhance both oxygen evolution reaction activity and durability of Gd₂Ru₂O_7‐δ through partial replacement with Na⁺ in Gd³⁺ sites is first offered, leading to the electronic and geometric regulation of active center RuO₆. Na⁺ triggers the emergence of Ru^<4+ and the electron rearrangement of active‐centered RuO₆. Specifically, Ru ions with a negative d‐band center after Na⁺ doping exhibit weaker adsorption energies of *O and result in the conversion of the rate‐limiting step from *O/*OOH to *OH/O*, reducing energy barriers for boosting activities. Therefore, the Na_xGd_2‐xRu₂O_7‐δ requires a low overpotential of 260 mV at 10 mA cm⁻² in 0.1 m HClO₄ electrolyte. Moreover, the higher formation energy of Ru vacancy and less distorted RuO6 enable the as‐prepared Na_xGd_2‐xRu₂O_7‐δ to operate steadily at 10 mA cm⁻² for 300 h and multi‐current chronopotentiometry with current densities from 20 to 100 mA cm⁻² for 60 h in acidic proton exchange membrane electrolyzer, respectively.