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

XY Qiu and V Pawlik and S Zhou and J Tao and YA Xia, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 145, 13400-13410 (2023).

DOI: 10.1021/jacs.3c03682

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 kinetic rate is slow enough to initiateasymmetrical one-side growth but fast enough to outpace surface diffusion;Au tetrahedral subunits are successively proliferated along the axial⟨110⟩ direction of Pd decahedra to form Pd-AuJanus icosahedra. Composed of five Pd and 15 Au tetrahedral subunits,such a heterogeneous icosahedron supports high (2.2 GPa) tensile strainand high strain difference up to +21.9%. In contrast, 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 ⟨211⟩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%).

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