Synthesis of mixed bismuth halide perovskites M3Bi2I6Br3 (M = Cs, K) encapsulated in floating substrates with high efficiencies for visible-light-driven CO2 and H2O conversion

The constant research for sustainable alternatives to address the global energy and environmental crisis has led to a renewed focus on solar energy as a clean and renewable energy source. Due to their unique optical and electronic properties, mixed halide perovskites offer a promising platform for CO₂ conversion. Therefore, this work proposed the synthesis of mixed halide perovskites based on M₃Bi₂I₆Br₃ (M = Cs, K) for visible-light-driven CO₂ and H₂O conversion. The mixed perovskites were immobilized in floated (porous) substrates for easier application and easy recovery of the materials. The mixed perovskites exhibited better crystallinity, higher light absorption, and lower recombination of the photogenerated charges than the reference materials (M₃Bi₂I₉). These properties promoted higher CO₂ and H₂O conversion efficiencies to generate HCOOH (3,170 µmol) and H₂ (160 µmol), respectively. Although the efficiency of Cs₃Bi₂I₆Br₃ was higher than that of K₃Bi₂I₆Br₃, it was possible to reach the efficiency for CO₂ reduction of Cs₃Bi₂I₉. Finally, the formation of a passive layer of BiOX (X = I, Br) on the K₃Bi₂I₆Br₃ surface was demonstrated, which eventually reduced the efficiency of the CO₂ reduction.