Proton exchange membrane (PEM) fuel cells and electrolyzers are promising renewable electrochemical energy storage and conversion technologies. Oxygen electrocatalysis remains the bottleneck of the efficiency of these devices due to sluggish reaction kinetics, high cost, and scarcity of state-of-the-art catalytic materials. Though the vast majority of research is focused on the discovery of new catalytic materials, understanding the solid-liquid interface especially the effects due to acid electrolyte anions and pH is crucial to designing and optimizing existing electrocatalysts under diverse electrochemical microenvironments. In this work, first, we systematically studied the effect of acid electrolytes on IrO2 for OER and Pt, Pd, and Ag for ORR. We further evaluated anion adsorption energies, dipole-field interactions, surface work function changes, Bader charges of adsorbed anions, and the effects of adsorbed electrolyte anions on the ORR and OER activity. Next, we developed microkinetic models that incorporate the effects of the electric field under ORR and OER reaction conditions to predict and compare the onset potentials, 2e vs 4e activity, Tafel slopes, and pH effects with experiments. This expansion of fundamental understanding of the effects of acid electrolyte anion adsorption and pH assists in engineering better-performing catalysts with integrated microenvironments for oxygen electrocatalysis.
