Metal–oxygen bonding characteristics dictate activity and stability differences of RuO2 and IrO2 in the acidic oxygen evolution reaction†

Abstract

Ruthenium dioxide (RuO₂) and iridium dioxide (IrO₂) serve as benchmark electrocatalysts for the acidic oxygen evolution reaction (OER), yet their intrinsic activity–stability relationships remain elusive. Herein, we employ density functional theory (DFT) calculations to systematically investigate the origin of divergent OER catalytic behaviors between RuO₂ and IrO₂ in acidic media. Mechanistic analyses reveal that RuO₂ follows the adsorbate evolution mechanism with superior activity (theoretical overpotential: 0.698 V vs. 0.909 V for IrO₂), while IrO₂ demonstrates enhanced stability due to a higher dissolution energy change (>2.9 eV vs. −0.306 eV for RuO₂). Electronic structure analysis reveals that RuO₂ exhibits ionic-dominated metal–oxygen bonds with delocalized electron distribution, facilitating intermediate desorption but promoting detrimental RuO₄²⁻ dissolution. In contrast, IrO₂ features covalent bonding characteristics with more electron filling in Ir–oxygen bonds (2.942 vs. 2.412 for RuO₂), thereby stabilizing surface intermediates against dissolution at the expense of higher OER barriers. This work establishes a clear correlation between the bonding nature and electrocatalytic performance metrics, offering fundamental insights for the rational design of acid-stable OER electrocatalysts with optimized activity–stability relationships.