Twin Proliferation and Prolongation under Kinetic Control: Pd-Au Janus Icosahedra versus Pd@Au Core-Shell Starfishes

摘要

Heterogeneous bimetallicnanocrystals featuring explicit spatialconfigurations and abundant twin defects can simultaneously enablegeometric and ligand effects to enhance catalytic and photonic applications.Herein, we report two growth patterns of Au atoms on penta-twinnedPd decahedra, involving twin proliferation to generate asymmetricPd-Au Janus icosahedra and twin elongation to produce anisotropicPd@Au core-shell starfishes, respectively. Mechanistic analysisindicates that the injection rate determines the lower-limit number(n (low)) of Au(III) ions in the steady stateand thus controls the growth pattern. When n (low) 5.5, the fast reduction kinetics promotessymmetric growth with inadequate surface diffusion. As such, Au atomsare laterally deposited along five high-indexed LeftAngleBracket;211RightAngleBracket;ridges of Pd decahedra to generate concave Pd@Au core-shellstarfishes with tunable sizes (28-40 nm), twin elongation ratios(33.82-162.08), and lattice expansion ratios (8.82-20.10).