Decoupling Intrinsic Metal Ion Reduction Rates from Structural Outcomes in Multimetallic Nanoparticles
Jacob Harrison Smith, Qi Luo, Shelby L. Millheim, Jill E. Millstone
Abstract
Simultaneously controlling both stoichiometry and atom arrangement during the synthesis of multimetallic nanoparticles is often challenging, especially when the desired metal precursors exhibit large differences in their intrinsic reduction kinetics. In such cases, traditional synthetic methods often lead to the formation of exclusively phase-segregated structures. In this study, we demonstrate that the relative reduction kinetics of the metal precursors can be manipulated independently of their intrinsic differences in reduction rates by modulating the instantaneous concentrations of the metal cation precursors. We achieve this control by adjusting the precursor addition rate, which decouples chemical ordering outcomes from differences in precursor reduction kinetics. To guide these experiments, we describe a quantitative model to determine how metal ion reduction rates evolve with variations in the precursor addition rate and thereby predict optimal conditions for the synthesis of multimetallic nanoparticles with precise structural and compositional outcomes. We demonstrate the efficacy of this model experimentally by synthesizing both core@shell and alloyed nanoparticles with stoichiometric control using the same metal ion precursors in two different bimetallic systems (Au-Pd and Au-Pt) as well as in a quinary metal system (Co, Ni, Cu, Pd, and Pt). This approach enables the design of nanoparticle architectures independent of intrinsic differences in metal ion reduction potentials of the constituent metals while maintaining both stoichiometric and structural control.