Modulating the Ruthenium‐Cobalt Active Pair with Moderate Spacing for Enhanced Acidic Water Oxidation

Ruthenium (Ru)-based catalysts have emerged as promising alternatives to Iridium (Ir) catalysts in proton exchange membrane water electrolysis cells due to their lower price and excellent oxygen evolution reaction (OER) activity. However, their stability is compromised by generation of unstable high-valence Ru sites and oxygen vacancy in a lattice oxygen-mediated (LOM) pathway. Here, a low-load Ru site on a Barium (Ba)-doped Co₃O₄ (RuBa_xCo_3-xO₄) catalyst is developed with abundant Ruthenium─Cobalt (Ru─Co) pairs for enhanced acidic OER activity. The incorporation of Ba can efficiently modulate the lattice of Co₃O₄, creating Ru─Co active pairs with optimized spacing through compression stress. In situ characterizations exhibit contractive Ru─Co pairs that promote the rapid and direct coupling of ^*O─O^* radicals, bypassing the sluggish ^*OOH species and avoiding the oxygen vacancies, which can trigger the oxide path mechanism (OPM) for an efficient and stable OER process. As a result, the designed catalyst delivers a low overpotential of 219 mV to achieve a current density of 10 mA cm^-2, and also demonstrates excellent stability, maintaining performance over 50 h of continuous operation at a larger current density of 50 mA cm^-2. These findings highlight the potential of the RuBa_xCo_3-xO₄ catalysts for durable and efficient OER applications.