Sluggish oxygen reduction kinetics limit low temperature PEM fuel cell catalyst choices to costly platinum and platinum-containing alloys. Recent advances in alkaline membrane technology have made the reduction of oxygen in a basic environment a viable option, opening the door for silver catalysts, which become active enough to compete with platinum when compared on a cost basis.
In this study we probe the elementary mechanism of oxygen reduction on platinum and silver in acidic and basic environments. We compare cyclic voltammetry and rotating disk electrode experiments to density functional theory calculations to show the influence of the catalyst choice on the reaction pathway in each environment. We calculate free energy diagrams for various mechanisms as a function of operating potential and relate these to the associated overpotentials and kinetic currents on each metal. Furthermore we use a Sabatier analysis to identify properties of electrocatalytic materials with optimal performance in alkaline environments. These catalysts may offer an opportunity to surpass current PEM performance standards.