Multimetallic Noble Metal Nanocrystals: Synthesis, Characterization, and Applications

Multimetallic noble metal-based nanocrystals are recognized as highly efficient catalysts due to the synergistic interactions among their multiple components. These nanocrystals generally exist in two forms: alloys, where metals are homogeneously mixed, and core-shell structures, where metals are arranged heterogeneously. Each form exhibits distinct electronic interactions, leading to different catalytic properties. Understanding and controlling the synthesis of these nanocrystals is crucial for discovering new properties and enhancing catalytic applications. To achieve the designed synthesis of multimetallic alloy nanocrystals, we developed mechanisms that involve active hydrogen (H·, hydrogen atoms or radicals). By utilizing active hydrogen generated in situ on the surfaces of nuclei or seeds, we create localized off-equilibrium environments that facilitate synchronized metal reduction. This innovative approach addresses issues of thermodynamic phase segregation and variations in metal reduction kinetics, allowing us to exert exceptional control over nanoparticle size, composition, and compositional homogeneity. Consequently, we can synthesize homogeneous few-element and high-entropy alloy nanocrystals, which exhibit intriguing electronic interactions among their components, resulting in enhanced catalytic activities and stabilities during methanol oxidation and oxygen evolution reactions ( 1- 4). We also successfully synthesized a new class of core-shell nanocrystals, characterized by a less stable metal core and a noble metal shell. The growth of a noble metal skin on a less stable metal template is often hindered by galvanic replacement reactions, making synthesis challenging. We tackle this challenge by adjusting the reduction potential of the noble metal salt, effectively suppressing the galvanic replacement reaction. This strategy enables us to synthesize novel catalysts such as Ag@Au, Ag@Pt, Ag@Pd, Cu@Pd, and Ni@Pt nanocrystals.