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.