Leveraging bismuth immiscibility to create highly concave noble-metal nanoparticles

The nanoscale integration of metals with differences in structure and electronics, although important for manipulating surface adsorption, does not typically yield structures with well-defined morphologies in colloidal synthesis. To create structures with unusually undercoordinated surfaces, we leverage the immiscibility of face-centered cubic noble metals with rhombohedral Bi to synthesize well-defined nanostructures with controllable concavity. With Au, three distinct morphologies can be achieved: concave tetrahedra, stella octangula (dual tetrahedron), and concave stella octangula. With Pd, we synthesize concave tetrahedra. Structural and compositional analysis shows that only ∼6 × 10⁻⁶ moles of surface Bi are needed for realizing these morphologies. Electrocatalytic experiments and simulations reveal that, compared with non-Bi-directed concave nanoparticles, the concave Au architectures are highly active toward alcohol oxidation and that surface Bi is critical for adsorption. This integration of immiscible elements provides a powerful strategy for creating highly active nanoparticles with precision.