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

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.