Real-Time Electroanalytical Measurements of Dynamic Reaction Chemistry Provide Generalizable Mechanistic Considerations for Metal Nanoparticle Synthesis

The growth of metal nanoparticles is well understood to involve a combination of kinetic parameters as well as selective or nonselective passivation of surfaces by adsorbates. However, these influences are challenging to measure directly and in real time, which makes it difficult to define reaction mechanisms that are sufficiently detailed and specific to fully predict rather than retrospectively rationalize observed growth phenomena. In the present work, we demonstrate that open-circuit potential (OCP) measurements of the mixed potential of metal nanoparticle growth solutions represent a uniquely facile approach for directly identifying and understanding these complex chemical growth processes in an in situ and time-resolved manner. We combine OCP measurements of particle growth with point-in-time electron microscopy and elemental analysis to establish the power of OCP measurements even as a stand-alone approach. In doing so, we also uncover generalizable principles for synthetic design, such as the critical importance of precise changes in the chemistry of the growth solution at early time points and on short time scales in directing shape development trajectories, even when the faceted shape does not emerge until later in the growth process. Further, we validate the use of the mixed solution potential to directly distinguish between surface passivation and kinetic control of particle growth. Overall, although the chemical factors contributing to the mixed potential during particle growth are complex, a rich understanding of specific chemical mechanisms can be extracted from these OCP measurements.