Photocatalytic CO ₂ Reduction to Formate on Lead‐Free Cs ₃ Sb ₂ Cl ₉

Abstract Photocatalytic CO 2 reduction to value‐added chemicals using perovskites is being explored to mitigate CO 2 emissions. This study examines lead‐free antimony‐based Cs 3 Sb 2 Cl 9 halide perovskites for its photocatalytic CO 2 reduction activity in solid‐liquid mode. The primary product was found to be formic acid (HCOOH) in the liquid phase, along with carbon monoxide (CO) and methane(CH 4 ) in the gaseous phase. Cs 3 Sb 2 Cl 9 displayed a selectivity of 73% toward formic acid with a yield of 54 µmol g −1 h −1 . Further, the selectivity toward formic acid was enhanced to 90% by loading Ir/IrO X as a water oxidation catalyst onto Cs 3 Sb 2 Cl 9 . The Ir/IrO X was loaded by the thermal decomposition of iridium (III) acetylacetonate. The yield of formic acid (HCOOH) on the composite catalyst Cs 3 Sb 2 Cl 9 ‐Ir/IrO X improved to 75 µmol g −1 h −1 , suppressing the formation of gaseous products. This is the highest yield of formic acid reported for this class of materials. The catalyst stability was evaluated using different material characterization techniques. Further, the stability of the catalyst toward formic acid yield was studied throughout a 25‐h reaction.