Theoretical methodology for studying oxygen reduction reaction (ORR) on disordered binary alloy surfaces

The catalytic activity of disordered binary alloy metal surfaces is investigated for the oxygen reduction reaction (ORR) by generating free energy diagrams and performing calculations on d-band centers of alloys. The disorder was simulated using virtual crystal approximation; then, based on periodic, self-consistent density functional theory (DFT) methods, we calculated adsorption energies of reaction intermediates. Alternative pathway for ORR mechanism, involving proton/electron transfer to adsorbed oxygen and hydroxyl, is considered. The methodology was applied to (111) surface of Pd_xCu_1-x disordered binary alloys, with different values of x concentration. This study found that at the ORR equilibrium potential of 1.23 V, the reactivity of all surfaces is shown to be limited by the rate of OH removal from the surface. Among the surfaces studied, the surface of Pd_0.80Cu_0.20 shows the highest reactivity and is more active than other non-Pt alloys. These results are in excellent agreement with earlier experimental and theoretical work.