Quantifying hot carrier and thermal contributions in plasmonic photocatalysis

Hot carriers reducing thermal barriers Plasmonic catalysts can generate hot charge carriers that can activate reactants and, in turn, reduce the overall barrier to a reaction. Zhou et al. studied the decomposition of ammonia to hydrogen on a copper alloy nanostructure that absorbed light and generated electrons that activated nitrogen atoms on ruthenium surface atoms (see the Perspective by Cortés). By measuring reaction rates at different wavelengths, light intensities, and catalyst surface temperatures, the light-induced reduction of the apparent activation barrier was quantified. Science, this issue p. 69; see also p. 28 A Ru-Cu alloy plasmonic photocatalyst substantially reduced the thermal activation barrier for ammonia decomposition. Photocatalysis based on optically active, “plasmonic” metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.