Plasmonic Control of Multi-Electron Transfer and C-C Coupling in Visible-Light-Driven CO2 Reduction on Au Nanoparticles.

Artificial photosynthesis relies on the availability of synthetic photocatalysts that can drive CO2 reduction in the presence of water and light. From the standpoint of solar fuel production, it is desirable that these photocatalysts perform under visible light and produce energy-rich hydrocarbons from CO2 reduction. However, the multistep nature of CO2-to-hydrocarbon conversion poses a significant kinetic bottleneck when compared to CO production and H2 evolution. Here, we show that plasmonic Au nanoparticle photocatalysts can harvest visible light for multielectron, multiproton reduction of CO2 to yield C1 (methane) and C2 (ethane) hydrocarbons. The light-excitation attributes influence the C2 and C1 selectivity. The observed trends in activity and selectivity follow Poisson statistics of electron harvesting. Higher photon energies and flux favor simultaneous harvesting of more than one electron from the photocharged Au nanoparticle catalyst, inducing the C-C coupling required for C2 production. These findings elucidate the nature of plasmonic photocatalysis, which involves strong light-matter coupling, and set the stage for the controlled chemical bond formation by light excitation.