Cs₃Bi₂Br₉/g-C₃N₄ Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO₂ to CO

Abstract

Lead-free halide perovskite derivative Cs₃Bi₂Br₉ has recently been found to possess optoelectronic properties suitable for photocatalytic CO₂ reduction reactions to CO. However, further work needs to be performed to boost charge separation for improving the overall efficiency of the photocatalyst. This report demonstrates the synthesis of a hybrid inorganic/organic heterojunction between Cs₃Bi₂Br₉ and g-C₃N₄ at different ratios, achieved by growing Cs₃Bi₂Br₉ crystals on the surface of g-C₃N₄ using a straightforward antisolvent crystallization method. The synthesized powders showed enhanced gas-phase photocatalytic CO₂ reduction in the absence of hole scavengers of 14.22 (±1.24) μmol CO g^-1 h^-1 with 40 wt % Cs₃Bi₂Br₉ compared with 1.89 (±0.72) and 5.58 (±0.14) μmol CO g^-1 h^-1 for pure g-C₃N₄ and Cs₃Bi₂Br₉, respectively. Photoelectrochemical measurements also showed enhanced photocurrent in the 40 wt % Cs₃Bi₂Br₉ composite, demonstrating enhanced charge separation. In addition, stability tests demonstrated structural stability upon the formation of a heterojunction, even after 15 h of illumination. Band structure alignment and selective metal deposition studies indicated the formation of a direct Z-scheme heterojunction between the two semiconductors, which boosted charge separation. These findings support the potential of hybrid organic/inorganic g-C₃N₄/Cs₃Bi₂Br₉ Z-scheme photocatalyst for enhanced CO₂ photocatalytic activity and improved stability.