Anchoring subnanometric Cu4 clusters in graphitic-C3N5 for highly efficient CO2 photoreduction to ethanol†

We demonstrated a facile electrochemical treatment for in situ anchoring of subnanometric Cu₄ clusters in a graphitic C₃N₅ framework (Cu₄/C₃N₅), leading to remarkable improvements of photocatalytic reactivity and selectivity for CO₂ reduction to ethanol. In the absence of a sacrificial reagent, a record ethanol production activity of 32.2 μmol g⁻¹ h⁻¹ with 98.6% selectivity has been achieved under visible light irradiation (λ ≥ 420 nm). In situ characterizations and theoretical calculations reveal that the significant improvement of reactivity and selectivity should be attributed to the coexisting Cu⁺ and Cu⁰ double active-sites in Cu₄/C₃N₅ catalysts for a highly efficient C–C coupling process. More specifically, the electron enriched Cu⁰ active sites could efficiently promote adsorption/activation of CO₂ molecules to form *CO intermediates, which partially transferred to adjacent Cu⁺ sites for preferential C–C coupling to generate *COCO intermediates. After the subsequent hydrogenation process, the photocatalytic CO₂-to-ethanol conversion has been achieved.