Enhanced thermal stability of Au@Pt nanoparticles by tuning shell thickness: Insights from atomistic simulations

Abstract

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.