Photo-Induced Plasmonic Light Harvesting Dynamics and Chemical Transformations Monitored Via Picosecond Time-Resolved Ambient-Pressure X-ray Photoelectron Spectroscopy (TRAPXPS)

Combining plasmonic nanostructures with semiconductor catalysts is a promising strategy to enhance both optical and electronic characteristics of photocatalytic devices. However, improving device efficiencies requires more detailed knowledge of processes such as light-induced charge injection, carrier separation, as well as back electron transfer and electron-hole recombination. We employ picosecond time-resolved X-ray photoemission spectroscopy to probe charge-carrier dynamics and chemical transformations in gold nanoparticle (AuNPs) sensitized TiO₂ under UHV and near-ambient H₂O pressure conditions suitable for photoelectrochemical water splitting. The experiments provide an absolute measure of the amount of charge injected from AuNPs into the TiO₂ substrate as well as the back electron transfer dynamics from the perspective of the electron donor. Under UHV conditions, approximately two electrons are injected per NP and charge recombination is complete within less than 1 ns. The presence of water has a significant impact on interfacial dynamics. Recombination timescales are increased by up to several ns and accompanied by indications for more efficient charge injection. Both effects are beneficial for the photocatalytic efficiency of the heterosystem as they potentially increase exposure of reactants to interfacial charges. The results underline the importance of characterizing fundamental interfacial electron and chemical dynamics under reaction-like conditions. Experiments are complemented by ongoing theoretical efforts to disentangle the physics underlying the observed charge transfer dynamics using a combination of molecular dynamics simulations and density functional theory.