Electronic modulation of a single-atom-based tandem catalyst boosts CO₂ photoreduction to ethanol

In artificial photosynthesis, tandem catalysis has emerged as an attractive approach to promote CO2 reduction to value-added multi-carbon (C2+) products through sequential steps at distinct sites. Herein, we investigate the coordination of Cu single atoms (Cu SAs) on In2O3 to create a conceptual tandem photocatalyst with orbital hybridization for efficient CO2-to-C-2 conversion with stoichiometric O-2 produced in pure water. Our findings reveal that the In2O3 domain provides high-coverage *CO intermediates, while the 3-coordinated Cu SAs promote the key C-C coupling. In2O3/Cu-O-3 exhibits a remarkable ethanol yield rate of 20.7 mu mol 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 In2O3/Cu-O-3 enables OC-COH coupling and CO2-to-ethanol conversion through the pathway CO2 -> *COOH -> *CO -> *OCCOH -> *OCH2CH3 -> 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 In2O3/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.