Engineering Lattice Distortion in Ruthenium Oxide Enables Robust Acidic Water Oxidation via Direct O–O Coupling

Abstract Ruthenium is considered one of the most promising alternatives to iridium as an anode electrocatalyst for proton exchange membrane water electrolysis (PEMWE). However, Ru‐based electrocatalysts suffer from poor stability, primarily due to structural collapse under the harsh acidic conditions of oxygen evolution reaction (OER). Here, a design strategy is introduced that significantly enhances both the stability and activity of RuO₂ by switching the catalytic mechanism from the adsorbate evolution mechanism (AEM) to the oxide pathway mechanism (OPM). This is achieved through lattice distortion engineering using a co‐doping strategy involving large‐radius ions (Na⁺ and Hf ⁴⁺). The incorporation of Na⁺ and Hf ⁴⁺ into RuO₂ induces significant lattice distortion, shortening partial Ru─Ru bond distance and optimizing the electronic structure. This modification facilitates direct O–O radical coupling, as confirmed by in situ vibrational measurements and theoretical calculations. It can drive a current density of 1 A cm⁻² in a PEMWE device at 60 °C with 1.646 V and operates stably for 85 h at 0.5 A cm⁻². The present study highlights that optimizing the synergistic interaction between two adjacent Ru sites to promote direct O–O coupling is an effective strategy for enhancing the acidic OER performance of RuO₂.