Electronic modulation of a single-atom-based tandem catalyst boosts CO 2 photoreduction to ethanol

In artificial photosynthesis, tandem catalysis has emerged as an attractive approach to promote CO 2 reduction to value-added multi-carbon (C 2+ ) products through sequential steps at distinct sites. Herein, we investigate the coordination of Cu single atoms (Cu SAs) on In 2 O 3 to create a conceptual tandem photocatalyst with orbital hybridization for efficient CO 2 -to-C 2 conversion with stoichiometric O 2 produced in pure water. Our findings reveal that the In 2 O 3 domain provides high-coverage *CO intermediates, while the 3-coordinated Cu SAs promote the key C–C coupling. In 2 O 3 /Cu–O 3 exhibits a remarkable ethanol yield rate of 20.7 μmol g −1 h −1 with a high selectivity of 85.8%, achieved without any sacrificial agent and photosensitizer under visible-light irradiation. In situ spectroscopies and theoretical calculations confirm that In 2 O 3 /Cu–O 3 enables OC–COH coupling and CO 2 -to-ethanol conversion through the pathway CO 2 → *COOH → *CO → *OCCOH → *OCH 2 CH 3 → ethanol. A set of techniques including X-ray absorption spectroscopy reveal that the 3-coordinated Cu SAs exist in the Cu + state, exhibiting a strong electron-donating capability. The electronic interaction between Cu and In through p–d and d–d hybridizations in In 2 O 3 /Cu–O 3 induces electron redistribution, leading to adjustment of the d band center and electronic localization near the Fermi level, thus facilitating C–C coupling for ethanol production.