Dissociative mechanism of oxygen reduction reaction (ORR) on Pd-Cu disordered binary alloy metal surfaces: A theoretical study

Density functional theory (DFT) in conjunction with virtual crystal approximation is used to study the oxygen reduction reaction (ORR) as a function of the cooper concentration in Pd-Cu disordered binary alloy metal surfaces and as a function of applied bias. The study is realized calculating the free energy diagrams of all intermediates. Reactivity is evaluated on the basis of an oxygen reduction reaction (ORR) dissociative mechanism of four steps, it involves the splitting of the O-O bond in O2 after its adsorption, followed by hydrogenation of atomic O to OH. Then, the OH species undergoes another hydrogenation to yield H2O. For each concentration of Cu, results for low oxygen coverage are presented at zero cell potential (U = 0), at the equilibrium potential (U = 1.23 V), and at the highest potential (U = 0.80 V) where all reaction are exothermic. The results indicate 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, while that at a cell potential of 0.80 V, the ORR reactivity of different surfaces is dictated by the hydrogenation of O* and strength of oxygen adsorption. The results are compared with other non-Pt alloys. (C) 2016 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.