Leveraging Bismuth Immiscibility to Create Highly Concave Noble Metal Nanoparticles

Noble metal nanoparticles can be designed to expose low- and high-index facets, providing precise control over the coordination environment of surface atoms. This control is essential for manipulating physical properties where surface adsorption is important, namely, sensing and catalysis. The integration of metals with differences in structure and electronics, while important for manipulating catalytic activity, does not typically yield structures with well-defined morphologies in colloidal synthesis. To create structures with unusually undercoordinated surfaces, here we leverage the immiscibility of incongruent crystal structures —Au and Bi — to synthesize and stabilize three distinct morphologies: concave tetrahedra, stella octangula (dual tetrahedron), and concave stella octangula. Structural and compositional analysis shows that only ~ 6 x10 -6 moles of surface Bi are needed to manipulate this morphology. Moreover, we show the generalizability of this methodology by synthesizing Pd concave tetrahedra with Bi-enriched surfaces. Electrocatalytic experiments reveal that these Au architectures are highly active toward alcohol oxidation, where surface Bi is critical for alcohol adsorption. Thus, integration of immiscible elements provides a new strategy for designing highly active nanoparticles with precision.