The Size Effect of PdCu Bimetallic Nanoparticles on Oxygen Reduction Reaction Activity

It is one of the basic objectives for heterogeneous catalysis to understand the particle size effect of nanoparticles (NPs) on their activity. However, such a particle size effect on the activity of bimetallic NPs is still in question. Here, we demonstrate an efficient ligand-assisted technique for preparing PdCu NPs in four different sizes (9.3 nm, 7.1 nm, 6.3 nm and 5.8 nm) and explore the relationship between particle size and their oxygen reduction reaction (ORR) activity as a benchmark. As a general trend, ORR activity decreases as bimetallic particle size increases. It is found that the 5.8 nm-PdCu NPs/C with the smallest size shows the best catalytic activity for ORR among these NPs, which exceeds the ORR activity of commercial Pt/C catalysts. Density functional theory (DFT) calculations confirm that, with the increase of bimetallic particle size, the edges and corners become less, and, accordingly, the adsorption energies of O atom and charge distribution of the particle are closer to the bulk phase, leading to the decrease of ORR catalytic activity. Our results provide a useful size controlled strategy and reveal the relationship between bimetallic particle size and reaction activity.