Nanoscale Energy Balance of a Plasmonic Antenna-Reactor Catalyst for Light-Driven Reactions: The Role of Hot-Carriers vs the Photothermal Effect

In plasmonic photocatalysis, the performance of a catalyst is enhanced by incorporating a plasmonic metal nanostructure. In this context, the so-called "antenna-reactor" configuration has been shown to be an ideal arrangement with distinct plasmonic and catalytic components that act as light-antennas and reaction sites, respectively. The light harvesting plasmonic nanoantenna captures and concentrates photonic energy and provides it to the reactor, <i>i.e</i>., the catalyst, for the catalytic reactions of interest taking place on its surface. In this study, we compare different antenna-reactor configurations, delving into the antenna-reactor working mechanism at the nanoscale. While the overall enhancement in catalytic activity of such systems is commonly reported, it is a matter of much debate to which extent this is caused by hot-carriers or by the photothermal effect. In this work, this gap in understanding is addressed through an energy balance analysis of the antenna-reactor system. The results show that only <1% of the absorbed energy is utilized for hot-carrier-driven activity, yet resulting in a 4-fold enhancement in the rate constant. Considering thermal effects, it is shown that either a very high light intensity (>5 sun irradiance for 4 cm² films) or system size (>100 cm² film for 1 sun irradiance) is required to attain accurately measurable increases in temperature. This work shows how combining classical electromagnetic and heat transfer analysis can yield clear quantitative mechanistic insights into plasmonic photocatalysis.