Searching for Evidence of Plasmonic Hot Carrier-Driven Photocatalysis for Ethanol Oxidation on Core-Shell Au-Pd Nanoparticle Photoelectrodes.

Plasmonic Au-Pd core-shell nanoparticle films were made to characterize plasmonic hot carrier-driven ethanol oxidation. Ultrafast transient absorption spectroscopy and photomodulated cyclic voltammetry were used to evaluate light-matter interaction and photocatalytic dynamics and performance. Increasingly thicker Pd shells quenched the excited state and catalytic photocurrent decreased substantially. Given that excited state quenching is generally ascribed to the creation/transfer of hot carriers, the decline in photocurrent was unexpected. Analyzing the photocurrent dynamics, the Au-Pd core-shell samples exhibited a thermal waveform, indicative of a plasmonic photothermal mechanism. Ultimately, we find photocatalysis in this system is better explained by simple Arrhenius enhancement of the dark current by plasmonic photothermal heating, rather than hot carrier-driven redox chemistry. Attenuated photocurrent upon addition of Pd is attributed as the indirect result of the dark current itself decreasing. For each sample, the photocurrent reflected an Arrhenius thermal enhancement corresponding to a temperature increase of +0.2 K (for 500 ms illumination). The prevalence of photothermal photocurrent and the samples having the same thermal outcome suggest that hot carriers, if created, overwhelmingly recombine to produce heat. Results here might offer insight into other plasmonic systems, especially where the photocurrent or photoproduct exhibits a photothermal waveform.