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-C₂ conversion with stoichiometric O₂ 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–O₃ 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 In₂O₃/Cu–O₃ 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–O₃ 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.