Role of Water Solvation on the Key Intermediates Catalyzing Oxygen Evolution on RuO₂

RuO2 and IrO2 are among the mostactive catalystsfor the Oxygen Evolution Reaction (OER). Recently, it was demonstratedthat the catalytic surface of these oxides plays a role in the reaction,where a hydrogen bond with a neighbor OH group stabilizes an unconventional-OO intermediate (-OO-H), prior to O-2 evolution. Quantum chemical calculations neglecting solvation effectsindicated that this intermediate is more stable than the conventional-OOH, and that deprotonation of the stabilizing -OHis the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water moleculeson the relative stability of -OOH and -OO-H oxygenateson RuO2 (110) by means of density functional theory calculationscombined with ab initio Molecular Dynamics simulations (AIMD). Weshow that the two intermediates participate in a hydrogen bondingnetwork with water to a similar extent, but leading to different interfacialwater structures, with possible implications on interfacial protondynamics and reaction kinetics. Moreover, -OOH can spontaneouslyconvert to -OO-H through a process mediated by water,demonstrating the critical role of explicitly including water in themodel. This study provides further mechanistic insights on the roleof the oxide surface chemistry in the OER mechanism and highlightsthe importance of explicitly treating the catalyst/water interfacesincluding dynamical aspects to assess the stability and the interconversionmechanism of key surface species, since the adoption of static solvationapproaches tends to overestimate the energetic difference between-OOH and -OO-H reaction intermediates.