Catalytic Activity of Pd/Cu Random Alloy Nanoparticles for Oxygen Reduction

Trends in oxygen reduction activity of Pd/Cu bimetallic random alloy nanoparticles are determined with calculations of oxygen binding for a range of compositions. A reduction in the average oxygen binding is found as Cu is added to Pd, indicating an increase in catalytic activity up to a peak at 1:1 Pd/Cu ratio. Calculations show that Cu reduces the Pd-O binding energy and Pd increases the Cu-O binding energy. These changes are understood in terms of charge transfer from Pd to Cu, lowering the d-band center of Pd and raising that of Cu. The peak in activity occurs because these two effects not equivalent. A greater overlap between the d-states of Pd and the adsorbed oxygen makes the reduction in binding at Pd more significant than the increase in binding at Cu. We present a simple model of the average binding energy that can generally predict activity trends in random alloys.