Molecular Dynamics Simulations of Thermally Induced Surface and Shape Evolution of Concave Au Nanocubes: Implications for Catalysis

High-index faceted concave nanoparticles have drawn widespread attention over the past few years because of their exceptional properties and promising applications. Their surface structures, especially steps, sharp corners, and edges, could serve as highly active sites to boost the catalytic activity and selectivity. In this work, we systematically investigated surface and shape evolutions of concave Au nanocubes, respectively, bounded with {210}, {310}, and {410} high-index facets during heating by molecular dynamics simulations. Convex Au nanocubes enclosed by these facets were also addressed for comparison. Our results demonstrated that the concave nanocubes possessed significantly higher fractions of surface atoms and remarkably lower averaged coordination numbers than the convex ones. Although the melting points of all the nanocubes were approximately equal, independent of their surface structures, the thermal stability of the surface and shape of the concave nanocubes was markedly inferior to that of the convex ones. The critical temperature of shape transformation follows the order of {210} < {310} < {410} in the concave nanocubes, while the reverse order was observed in the convex nanocubes. Our work suggests that there should be a selective compromise between high fractions of low-coordinated surface atoms and the stable surface structure for applications of concave nanoparticles. This work extends the fundamental understanding about the temperature-dependent surface structure of metallic nanoparticles with high-index facets, and provides a theoretical reference for enhancing their thermodynamic stability.