Sunlight plays a critical role in the development of emerging sustainable energy conversion and storage technologies. Light-induced CO₂ reduction by artificial photosynthesis is one of the cornerstones to produce renewable fuels and environmentally friendly chemicals. Interface interactions between plasmonic metal nanoparticles and semiconductors exhibit improved photoactivities under a wide range of the solar spectrum. However, the photo-induced charge transfer processes and their influence on photocatalysis with these materials are still under debate, mainly due to the complexity of the involved routes occurring at different timescales. Here, we use a combination of advanced in situ and time-resolved spectroscopies covering different timescales, combined with theoretical calculations, to unravel the overall mechanism of photocatalytic CO₂ reduction by Ag/TiO₂ catalysts. Our findings provide evidence of the key factors determining the enhancement of photoactivity under ultraviolet and visible irradiation, which have important implications for the design of solar energy conversion materials.

Supported nanoparticles make the reaction faster: Several techniques now allow surface structures used as catalysts to be probed during exposure to reactive gases, as opposed to under vacuum conditions. Divins et al. used near-ambient-pressure x-ray photoelectron spectroscopy to compare the effect of reaction gases on unsupported palladium-rhodium nanoparticles versus ones on a reducible cerium oxide support. For the reaction of ethanol with steam to produce hydrogen, the supported nanoparticles were more reactive and less prone to reduction and surface rearrangement. Science , this issue p. 620