Prolonging Charge Carrier Lifetime via Intraband Defect Levels in S‐Scheme Heterojunctions for Artificial Photosynthesis

Abstract S‐scheme heterostructure photocatalysts, distinguished by unique charge‐transfer pathways and exceptional catalytic redox capabilities, have found widespread applications in addressing challenging chemical processes, including the photocatalytic reduction of CO 2 with a high reaction barrier. Nevertheless, the influence of intraband defect levels within S‐scheme heterojunctions on charge separation, carrier lifetime, and surface catalytic reactions has, for the most part, been overlooked. Herein, we develop a tunable defect‐level‐assisted strategy to construct an electron reservoir, effectively prolonging the lifetime of charge carriers through the rapid capture and gradual release of photoelectrons within WO 3‐x /In 2 S 3 S‐scheme heterojunctions, as authenticated by femtosecond transient absorption spectroscopy and theoretical simulations. The surface photoredox mechanism, unraveled by Gibbs free energy calculations, demonstrates that oxygen‐vacancy‐induced defect states in WO 3‐x /In 2 S 3 heterojunctions unlock the rate‐determining H 2 O oxidation into free oxygen molecules by forming metastable oxygen intermediates, contributing to the facilitation of H 2 O photooxidation. This distinct role, combined with the extended carrier lifetime, results in boosted CO 2 photoreduction with nearly 100 % CO selectivity in the absence of any photosensitizer or scavenger. Our work sheds light on the role of controllable defect levels in governing charge transfer dynamics within S‐scheme heterojunctions, thereby inspiring the development of more advanced photocatalysts for artificial photosynthesis.