Watching Visible Light-Driven CO₂ Reduction on a Plasmonic Nanoparticle Catalyst

Photocatalytic reduction of carbon dioxide (CO 2 ) 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 2 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 2 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 2 leading to the formation of HOCO*, indicating close interplay between photoexcited states and adsorbate/metal interactions.