Compositional Inhomogeneity and Corner Enrichment of Pt in Pt/Pd Bimetallic Nanoparticles

Experimental results of a smooth composition gradient within Pt/Pd alloy nanoparticles with Pt enrichment at the corners are reported. We find that the Pt concentration gradually increases toward the outermost surface, and it appears different from the thermodynamically most stable configuration. We demonstrate that it is the result of reaction kinetics of both the reduction of precursors and growth of nanoparticles, by a growth model. We then explain that the corner Pt enrichment is a result of local thermodynamic control at the corners. This mixed control of kinetics and thermodynamics in bimetallic nanoparticle synthesis can lead to the formation of particles with a complex concentration profile, which could be interesting when these particles are used in catalytic applications. Our analysis is not simply a qualitative model but rather a relatively rigorous quantitative analysis of the composition as a function of the growth conditions, which can serve as a basis for improved reproducibility of synthesis for applications.