Double Z-scheme in SnO2/SnS2/Cu2SnS3 heterojunction for photocatalytic reduction of CO2 to ethanol

Photocatalytic reduction of CO2 to chemical fuels enables a sustainable way of reducing carbon emissions but faces a high reduction potential due to the high stability of CO2 molecules. Here, we prepared a SnO2/SnS2/Cu2SnS3 double Z-scheme heterojunction photocatalyst, in which SnO2, SnS2, and Cu2SnS3 absorb ultraviolet, visible, and near-infrared light, respectively. Based on the comprehensive analysis of in-situ X-ray photoelectron spectroscopy and photo(chemical) characterizations, we find that the photogenerated electrons would transfer from SnO2 to SnS2 to Cu2SnS3. The optimized SnO2/SnS2/Cu2SnS3-0.3 double Z-scheme heterojunction could achieve 28.44 μmol g–1 h–1 ethanol yield and 92% selectivity, which is roughly 3 folds higher than SnO2/SnS2 single Z-scheme heterojunction. By using in-situ diffuse reflectance infrared Fourier-transform spectroscopy, we observe that ethanol is produced through a *COCOH pathway, in which Cu2SnS3 would decrease the activation energy barrier from *COOH to *CO.