Overcoming the oxygen reduction reaction (ORR) barrier in PEM fuel cells generally limits cathode catalyst choices to platinum or platinum-containing alloys. These materials are costly and still lack activities high enough to make widespread implementation economical. Recent advances in alkaline membrane technology have made the reduction of oxygen in a basic environment a viable option for low temperature fuel cells. In basic medium, silver catalysts become active enough to compete with platinum on a power-per-cost basis.
In this study we probe the elementary mechanism of oxygen reduction on platinum and silver in acidic and basic environments. We couple cyclic voltammetry and rotating disk electrode experiments with quantum chemical density functional theory calculations to show the influence of the choice of catalyst on the reaction pathways. We develop 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 electrocatalytic materials with optimal characteristics. These materials represent an opportunity to surpass acidic platinum catalysts in low temperature fuel cell applications.