Why Colloidal Syntheses\nof Bimetallic Nanoparticles\nCannot be Generalized

Introducing one general synthesis to form bimetallic\nnanoparticles\n(NPs) could accelerate the discovery of NPs for promising energy applications.\nAlthough colloidal syntheses can provide precise structural and morphological\ncontrol of bimetallic NPs, the complex chemical nature of multicomponent\nsyntheses challenges the realization of such synthetic simplicity.\nCommon synthetic issues are frequently ascribed to the variation in\nmetal ion precursor reactivities and complex chemical interactions\nbetween the different metal surfaces and capping agents employed.\nHowever, no systematic studies have shown how these factors compete\nto ultimately assign the factor limiting the mixing and formation\nof bimetallic NPs. Here, we provide a parametric investigation of\nhow the intrinsic standard reduction potentials (<i>E</i><sup>0</sup><sub>red</sub>) of the metal ions and cocapping agents\ninfluence the formation of bimetallic AuCu, AuPd, and PdCu NPs. Using\na combination of <i>in situ</i> X-ray total scattering along\nwith transmission electron microscopy and nuclear magnetic resonance\nspectroscopy, we illustrate the multifunctional role of the cocapping\nagents through interactions with both the metal ion precursors and\nNP surfaces to stabilize metastable structures. Additionally, we demonstrate\nhow system-specific side reactions and the local metal ion coordination\nenvironment can be used to selectively tune the formation kinetics,\nstructure, and morphology of bimetallic NPs. Ultimately, these insights\nshow that the chemical interactions rather than the intrinsic <i>E</i><sup>0</sup><sub>red</sub> are responsible for the formation\nof bimetallic NPs. Broadly, these insights should aid the synthetic\ndesign of tailored multimetallic NPs.