Nanoparticle phase transformations and their transient states underlie many technologies in energy storage, memory, and catalysis. However, modifying these intermediate states requires bridging the length-scale gap between the atomic-scale structural features (such as atomic coordination number and surface strain) that influence dynamics and the macroscale extrinsic parameters (e.g. temperature, chemical environment) that can be controlled. Optical excitation of localized surface plasmon resonances (LSPRs) offers a solution for overcoming this size mismatch. Here, we use in situ environmental transmission electron microscopy coupled with optical illumination to demonstrate how LSPRs enable spatially-modified phase transformation dynamics in nanoparticles. As a model reaction, we study the gas-phase photocatalytic dehydrogenation of a variety of Au-Pd systems, in which the Au acts as a plasmonic light absorber and Pd serves as the catalyst. Under controlled hydrogen pressures, temperatures, and illumination conditions, we study the study the kinetics of the desorption reaction triggered by the optical excitation of plasmons. We find that plasmons control photochemistry in three ways. First, plasmons modify the rate of distinct reaction steps differently, increasing the overall rate more than ten-fold. Secondly, plasmons open new reaction pathways that are not observed without illumination. Finally, reaction nucleation occurs at electromagnetic hot-spots – even when those hot-spots do not occur in the preferred nucleation site. Our results help elucidate the role of plasmons in light-driven phase transformations, en-route to design of site-selective and product-specific photocatalysts.

Driving energetically unfavorable dehydrogenation dynamics with plasmonics

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.