Watching Visible Light-Driven CO Reduction on a Plasmonic Nanoparticle Catalyst.

Photocatalytic reduction of carbon dioxide (CO) by visible light has the potential to mimic plant photosynthesis and facilitate the renewable production of storable fuels. Accomplishing desirable efficiency and selectivity in artificial photosynthesis requires an understanding of light-driven pathways on photocatalyst surfaces. Here, we probe with single-nanoparticle spatial resolution the dynamics of a plasmonic silver (Ag) photocatalyst under conditions of visible light-driven CO reduction. In situ surface-enhanced Raman spectroscopy captures discrete adsorbates and products formed dynamically on single photocatalytic nanoparticles, most prominent among which is a surface-adsorbed hydrocarboxyl (HOCO*) intermediate critical to further reduction of CO to carbon monoxide (CO) and formic acid (HCOOH). Density functional theory simulations of the captured adsorbates reveal the mechanism by which plasmonic excitation activates physisorbed CO leading to the formation of HOCO*, indicating close interplay between photoexcited states and adsorbate/metal interactions.