Robust Junction Formation of Copper(I) Oxide on Graphitic Carbon Nitride Enhances Aqueous Carbon Dioxide Photoreduction without Sacrificial Reagents

Semiconductor hybrid structures containing multiple components have been considered an ideal photocatalyst design to generate long‐lived charge‐separated states. The reaction activity is highly susceptible to the catalyst component and morphology, particularly for the reactions requiring high activation energies, such as a CO2 reduction reaction (CO2RR). In this study, we selected g‐C3N4 and Cu2O as photocatalytic components having bandgaps suitable for CO2RR. Our approach involved establishing robust electric junctions between these domains by direct growth of Cu on g‐C3N4 via a polyol process. The resulting g‐C3N4/Cu2O hybrid was employed as photocatalysts in an aqueous medium without hole acceptors. The catalyst exhibited notable activities for CO (94 μmol gcat−1 h−1) and CH4 production (218 μmol gcat−1 h−1), maintaining stability for over 6 h. The inherent synergy between g‐C3N4 and Cu2O, facilitated by the formation of conductive junctions, enabled efficient electron transfer to promote CO2RR. These findings ensured the importance of junctions and interfaces in the hybrid catalyst structures for unlocking superior photocatalytic CO2RR performance. Robust and well‐defined heterojunctions were formed by growing Cu2O nanocubes directly on the g‐C3N4 sheets. The resulting g‐C3N4/Cu2O hybrids exhibited high photocatalytic activities of CO2 reduction into CO and CH4 with oxygen evolution in aqueous medium without sacrificial reagents.