Session: Nanomaterials:

Light-driven chemistry is gaining traction as an important source for fuels and value-added chemicals because of the potential for unique chemical transformations, enhanced efficiency, and the capture of solar energy. Nanoparticles (NPs) have proven to be a promising platform for such chemistry, as their small size enables charges to migrate to surface-bound catalysts, where they are used in a reaction. Recent work describes the development of blended PTB7-Th (donor):EH-IDTBR (acceptor) organic NPs. When loaded with platinum, these NPs exhibit impressive rates of Hydrogen Evolution Reaction (HER). By virtue of their blended morphology, donor and acceptor regions are separated by a high surface area internal heterojunction, which facilitates exciton dissociation into free charges. Once separated, free electrons in the acceptor regions are shuttled to a surface-bound Pt co-catalyst where they perform HER, while holes in the donor regions are scavenged by ascorbic acid. Herein, we study the relationship between nanoparticle structure, charge carrier dynamics, and photocatalytic activity using Time-Resolved Microwave Conductivity (TRMC). TRMC is uniquely capable of directly evaluating the yield, mobility, and kinetics of free charges in low-mobility organic materials by measuring the change in a microwave’s power as it propagates through a sample. TRMC is blind to the identity of a charge carrier, so systems must be designed such that one carrier is confined while the other remains mobile. In such a system, attenuations in microwave signal can be directly attributed to the mobile carrier. Pt-loaded blended NPs are an ideal candidate for study by TRMC, since it is thought that electrons are confined to the Pt co-catalyst while holes remain mobile within the donor region. Compared to NPs lacking Pt co-catalyst, we expect Pt-loaded NPs to show a reduced TRMC signal, corresponding to the loss of electron signal, and a longer lifetime, due to reduced carrier recombination. This work examines how a nanoparticle’s structure or solvated environment impacts the generation of charges and asks how we can promote the migration of charges to a nanoparticle’s surface while minimizing recombination.

Max O'Connor

Graduate Student Researcher, University of Colorado, Boulder

Appearances