Simultaneous Photo Protecting and Tuning Selectivity of Cs₃Bi₂Cl₉ during Photoreduction of CO₂ to HCOOH Using Ir/IrO_X

Tuning the selectivity with the improved activity of photocatalysts during the photoreduction of CO₂ to value-added chemicals is one of the main bottlenecks in the field of artificial photosynthesis. Here we have investigated lead-free, bismuth-based Cs₃Bi₂Cl₉ perovskites as photocatalysts for the photoreduction of CO₂in the solid-liquid phase. The main CO₂ photoreduction products include CO, CH₄ in the gas phase, and HCOOH in the liquid phase. Cs₃Bi₂Cl₉showed high activity and good selectivity towards HCOOH, with a 553 ± 21 µmol g^-1 yield at the end of the 5-hour reaction. There was decreased activity of the Cs₃Bi₂Cl₉ due to the formation of the secondary phase of BiOCl. A composite photocatalyst Cs₃Bi₂Cl₉-Ir/IrO_X showed a higher selectivity towards HCOOH with a yield of 789 ± 43 µmol g^-1 at the end of the 5-hour reaction which was 1.5 times higher than the yield on pristine material. This was the highest yield of HCOOH ever reported for this class of materials. The presence of Ir/IrO_X provided the reaction with much-needed hydroxyl groups for the photoreduction of CO₂. Further, Ir/IrO_X delayed the catalyst deactivation thereby retaining its activity for longer cycles by altering the photo-generated charge recombination process and prolonging their lifetimes making them available for the valuable photoreduction of CO₂. This work provides a simple yet effective strategy to tune the selectivity and improve the performance of photocatalysts for CO₂ photoreduction.