Chemisorption-mediated ultrafast charge transfer at the CO2 photoreduction interface.

We employ femtosecond transient absorption spectroscopy to probe ultrafast charge transfer at the CO2 reduction interface in situ. We uncover hitherto unrecognized chemisorption states, formed through orbital hybridization between chemisorbed species and active sites, as efficient hole traps to prolong the lifetime of photogenerated electrons, underpinning the enhanced photocatalytic activity.