Origin of Enhanced Activities for CO Oxidation and O<sub>2</sub> Reaction over Composition-Optimized Pd<sub>50</sub>Cu<sub>50</sub> Nanoalloy Catalysts

It has been shown experimentally that Pd<sub>50</sub>Cu<sub>50</sub> nanoalloy achieves the maximum activity for CO oxidation (COox) and oxygen reduction reaction (ORR) on composition-tuned PdCu bimetallic catalysts, but the origin of this catalytic synergy remains unclear. In this work, results of our density functional theory (DFT) calculations show that the weakest adsorption strength of O<sub>2</sub> in terms of the most pronounced charge transfer between Pd and Cu is responsible for the experimentally observed highest catalytic activity of Pd<sub>50</sub>Cu<sub>50</sub> catalyst for both COox and ORR over a series of composition-tuned PdCu nanoalloys. For COox, the lowest barrier energy is attributed to the weakest adsorption strength of O<sub>2</sub> on Pd<sub>50</sub>Cu<sub>50</sub> catalyst. In ORR, the lowest barrier energy for O<sub>2</sub> dissociation and also the weakest adsorption strength of O, OH, and OOH species are related to the weakest adsorption strength of O<sub>2</sub> over the catalyst with a 50:50 ratio of Pd/Cu. Our work represents the first attempt to address an in-depth correlation between the theoretical and experimental data on the highly active PdCu catalysts, the results of which has significant implications for the design of advanced nanoalloy catalysts with superior catalytic synergy in terms of the alloy compositions.