Highly Selective Photoconversion of CO2 to CH4 over SnO2/Cs3Bi2Br9 Heterojunctions Assisted by S-Scheme Charge Separation

Exploring photocatalysts to promote the conversion of CO2 to valuable chemical fuels is a highly promising approach for mitigating energy scarcity and environmental pollution. Lead-free perovskite Cs3Bi2Br9 quantum dots (QDs) have attracted considerable attention in CO2 photoreduction due to the robust reduction capability and controllable product selectivity. Nevertheless, their potential has been impeded by the rapid recombination of charge carriers, leading to unsatisfactory photocatalytic efficiency. Here, unique SnO2/Cs3Bi2Br9 S-scheme heterojunctions are constructed by electrostatically self-assembling SnO2 nanofibers with Cs3Bi2Br9 QDs to enhance the CO2 photoreduction performance. Density functional theory calculations, along with experimental studies, reveal that electrons transfer from Cs3Bi2Br9 to SnO2, creating a directed interfacial electric field and bending the energy bands at the interfaces. This facilitates the transport of photoelectrons from SnO2 to Cs3Bi2Br9, forming SnO2/Cs3Bi2Br9 S-scheme heterojunctions and enabling the effective separation of powerful photoexcited electron/hole pairs. Additionally, profiting from the enhanced light absorption contributed by narrow-bandgap Cs3Bi2Br9 and the lower energy barrier for CH4 production over the Cs3Bi2Br9 surface, the SnO2/Cs3Bi2Br9 heterostructures unveil superior CO2 photoreduction activities with high selectivity for CH4 over 70%, without the assistance of any molecular catalyst or scavenger.