Multiscale Modeling of Mass Transport Effects on Oxygen Evolution Reaction Kinetics.

We develop a multiscale theoretical model integrating atomic-scale density functional theory (DFT), microkinetic simulations, and continuum transport models to elucidate the mass transport effects on the kinetics of the OER on IrO2 and RuO2 catalysts, which bridges atomic-level insights with macroscopic electrochemical behavior. By coupling constant potential DFT simulations of reaction energetics with microkinetic equations and Nernst-Planck-Poisson transport physics, we resolve atomic-scale reaction pathways under experimentally relevant concentration gradients. During the reaction process, significant variations in the concentrations of H+, OH-, and adsorbates are identified at the electrode surface under different potentials, leading to the local pH shifts and ion depletion at electrode interfaces, which fundamentally alter the rate-determining steps. The framework reproduces experimental Tafel slopes (39/146 mV/dec for RuO2; 59/118 mV/dec for IrO2) without empirical fitting, highlighting the critical role of ion concentration gradients in governing the reaction kinetics. Our unified framework emphasizes the mass transport imperative on revealing the reaction mechanisms in realistic electrochemical environments, offering a generalizable strategy for designing and evaluating the novel OER catalysts.