Size and Shape Effects of Pd@Pt Core-Shell Nanoparticles: Unique Role of Surface Contraction and Local Structural Flexibility

In this article, we present a density functional theory (DFT) study of nanoparticles (NPs) using a more realistic particle model, which allows us to model Pd@Pt core-shell NPs in size of 1-3 nm (number of atoms: 35-405) and shape [tetrahedron (TH); sphere-like truncated octahedron (SP)] precisely. Our results show that the size and shape have significant effects on the stability and activity of a Pd@Pt NP toward the oxygen reduction reaction (ORR). More importantly it is found for the first time that the variation in activity with particle size is shape-dependent. In addition, under the ORR conditions the adsorbate-driven structural changes on the terraces of nanoparticles can occur, which is relevant for understanding the observed activity and stability. According to our DFT calculations, the catalytic behaviors of Pd@Pt nanoparticles associated with the surface contraction (compressive strain) and the local structural flexibility, which are strongly size- and shape-dependent. Our study demonstrates the importance of modeling more realistic catalysts and in situ study under reaction conditions to draw valid conclusions for nanocatalysts.