Facilitating charge separation by constructing CuInS2/PCN S-scheme heterojunction with the intimate contact interface for enhanced photocatalytic CO2 reduction

Photocatalytic CO2 conversion efficiency is still much lower than what is expected owing to the sluggish charge separation and transfer for many semiconductors. Herein, we fabricated a highly efficient S-scheme heterojunction by integrating the CuInS2 (CIS) with the oxygen-doping brown polymer carbon nitride (PCN). The construction of CIS/PCN S-scheme heterojunction promotes spatial separation of photogenerated charge while maintaining their strong reduction capability. The formed intimate contact interface between the CIS and PCN provides the strong driving force for the transfer of photogenerated charge, which accelerates the electrons rapidly migrating from PCN to CIS through the tight interface, resulting in more reductive electrons participating in photocatalytic reaction. As a result, the CIS/PCN S-scheme heterostructure shows a remarkably enhanced photocatalytic activity with a CO yield rate of up to 105.89 μmol g-1h−1, which is 7 times higher than that of the CIS. Combined density functional theory (DFT) calculations with experimental results demonstrate the formation of an intimate contact interface is not only more conducive to CO2 adsorption and activation but also lowers the reaction energy barrier of the conversion of CO2 to CO. Meanwhile, ESR characterization reveals the electron transfer pathway of CIS/PCN for photocatalytic CO2 conversion. This work may provide an illuminating insight into designing the S-scheme photocatalyst for enhanced CO2 photoreduction.