Improved oxygen reduction reactivity of platinum monolayers on transition metal surfaces

The catalytic activity of platinum monolayers supported on close-packed transition metal surfaces (Au(1 1 1), Pt(1 1 1), Pd(1 1 1) and Ir(1 1 1)) is investigated for the oxygen reduction reaction (ORR) by generating free energy diagrams and performing Sabatier analysis based on periodic, self-consistent density functional theory (DFT) calculations. Three different ORR mechanisms, involving direct or hydrogen-assisted activation of O 2, are considered. 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. At a cell potential of 0.80 V, the ORR reactivity of different surfaces is dictated by the strength of oxygen adsorption, with OH removal via hydrogenation and O–O bond scission in either O 2, O 2H or H 2O 2 being the rate-limiting steps for surfaces with stronger and weaker oxygen binding, respectively. Among the surfaces studied, Pt monolayer on a Pd(1 1 1) substrate shows the highest reactivity and is more active than Pt(1 1 1). These results are in excellent agreement with our earlier experimental and theoretical work, which was based on a simpler model for the ORR.