Reductive Carbon–Carbon Coupling on Metal Sites Regulates Photocatalytic CO2 Reduction in Water Using ZnSe Quantum Dots

Colloidal quantum dots (QDs) consisting of precious‐metal‐free elements show attractive potentials towards solar‐driven CO2 reduction. However, the inhibition of hydrogen (H2) production in aqueous solution remains a challenge. Here, we describe the first example of a carbon–carbon (C−C) coupling reaction to block the competing H2 evolution in photocatalytic CO2 reduction in water. In a specific system taking ZnSe QDs as photocatalysts, the introduction of furfural can significantly suppress H2 evolution leading to CO evolution with a rate of ≈5.3 mmol g−1 h−1 and a turnover number (TON) of >7500 under 24 h visible light. Meanwhile, furfural is upgraded to the self‐coupling product with a yield of 99.8 % based on the consumption of furfural. Mechanistic insights show that the reductive furfural coupling reaction occurs on surface Zn‐sites to consume electrons and protons originally used for H2 production, while the CO formation pathway at surface anion vacancies from CO2 remains. Reductive carbon–carbon coupling was used to block H2 evolution in CO2 photoreduction in water. Furfural, one of the biomass platform molecules, adsorbs on Zn‐sites consuming electrons and protons originally used for H2 production, but the CO formation pathway at surface anion vacancies remains. Therefore, CO was evolved with a CO/H2 ratio of 265 : 1 in the gas phase and furfural was upgraded to value‐added hydrofuroin.