Enhanced Photocatalytic Reduction of CO₂ to CO Using Cs₃Bi₂Br₉/g-C₃N₄ Direct Z-Scheme Heterojunctions

Lead-free halide perovskite derivative Cs₃Bi₂Br₉, has proven to possess optoelectronic characteristics suitable for photocatalytically reducing CO₂ to CO. However, further research is needed to boost the separation of charges in order to improve the overall efficiency of this photocatalyst. This study presents the synthesis of a hybrid heterojunction composed of inorganic and organic materials, combining Cs3Bi2Br9 with g-C₃N₄ at various ratios. This was accomplished by growing Cs₃Bi₂Br₉ crystals on the surface of g-C₃N₄ using a straightforward antisolvent crystallization method. The resulting powders demonstrated increased photocatalytic CO₂ reduction in the gas phase with water vapor, producing 14.22 (±1.24) μmol of CO per gram per hour with a 40% Cs₃Bi₂Br₉ content, compared to 1.89 (±0.72) and 5.58 (±0.14) μmol CO g^–1 h^–1 for pure g-C₃N₄ and Cs₃Bi₂Br₉, respectively. Photoelectrochemical measurements revealed enhanced photocurrent in the composite further proving improved charge separation. Additionally, stability tests showed that the heterojunction remained structurally stable even after 15 hours of illumination. Analysis of the band structure alignment and selective metal deposition indicated the formation of a direct Z-scheme heterojunction between the two semiconductors, which led to a significant improvement in charge separation and an overall enhancement in CO₂ reduction.<sup>1

1</sup> Baghdadi, Y. et al. Cs₃Bi₂Br₉/g-C₃N₄ Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO2 to CO. Chemistry of Materials, doi:10.1021/acs.chemmater.3c01635 (2023).