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

Exploring photocatalysts to promote the conversion of CO 2 to valuable chemical fuels is a highly promising approach for mitigating energy scarcity and environmental pollution. Lead-free perovskite Cs 3 Bi 2 Br 9 quantum dots (QDs) have attracted considerable attention in CO 2 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 SnO 2 /Cs 3 Bi 2 Br 9 S-scheme heterojunctions are constructed by electrostatically self-assembling SnO 2 nanofibers with Cs 3 Bi 2 Br 9 QDs to enhance the CO 2 photoreduction performance. Density functional theory calculations, along with experimental studies, reveal that electrons transfer from Cs 3 Bi 2 Br 9 to SnO 2, creating a directed interfacial electric field and bending the energy bands at the interfaces. This facilitates the transport of photoelectrons from SnO 2 to Cs 3 Bi 2 Br 9, forming SnO 2 /Cs 3 Bi 2 Br 9 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 Cs 3 Bi 2 Br 9 and the lower energy barrier for CH 4 production over the Cs 3 Bi 2 Br 9 surface, the SnO 2 /Cs 3 Bi 2 Br 9 heterostructures unveil superior CO 2 photoreduction activities with high selectivity for CH 4 over 70%, without the assistance of any molecular catalyst or scavenger.