The stoichiometric photocatalytic reaction of CO₂ with H₂O is one of the great challenges in photocatalysis. Here, we construct a Cu₂O-Pt/SiC/IrO_x composite by a controlled photodeposition and then an artificial photosynthetic system with Nafion membrane as diaphragm separating reduction and oxidation half-reactions. The artificial system exhibits excellent photocatalytic performance for CO₂ reduction to HCOOH and H₂O oxidation to O₂ under visible light irradiation. The yields of HCOOH and O₂ meet almost stoichiometric ratio and are as high as 896.7 and 440.7 μmol g⁻¹ h⁻¹, respectively. The high efficiencies of CO₂ reduction and H₂O oxidation in the artificial system are attributed to both the direct Z-scheme electronic structure of Cu₂O-Pt/SiC/IrO_x and the indirect Z-scheme spatially separated reduction and oxidation units, which greatly prolong lifetime of photogenerated electrons and holes and prevent the backward reaction of products. This work provides an effective and feasible strategy to increase the efficiency of artificial photosynthesis.

The active center for the adsorption and activation of carbon dioxide plays a vital role in the conversion and product selectivity of photocatalytic CO₂ reduction. Here, we find multiple metal sulfides CuInSnS₄ octahedral nanocrystal with exposed (1 1 1) plane for the selectively photocatalytic CO₂ reduction to methane. Still, the product is switched to carbon monoxide on the corresponding individual metal sulfides In₂S₃, SnS₂, and Cu₂S. Unlike the common metal or defects as active sites, the non-metal sulfur atom in CuInSnS₄ is revealed to be the adsorption center for responding to the selectivity of CH₄ products. The carbon atom of CO₂ adsorbed on the electron-poor sulfur atom of CuInSnS₄ is favorable for stabilizing the intermediates and thus promotes the conversion of CO₂ to CH₄. Both the activity and selectivity of CH₄ products over the pristine CuInSnS₄ nanocrystal can be further improved by the modification of with various co-catalysts to enhance the separation of the photogenerated charge carrier. This work provides a non-metal active site to determine the conversion and selectivity of photocatalytic CO₂ reduction.

Compared to the pristine WO₃, the oxygen vacancy defect levels of the sub-stoichiometric WO_3−X narrow the bandgap and promote the separation of photogenerated electron–hole pairs.