Cs4Co1.2Sb1.8Cl12 with rich chlorine defect and enhanced spin polarization achieved excellent photocatalytic activity for CO2 conversion without sacrificial agent

To address the bottlenecks of sluggish carrie r separation and insufficient active sites in lead-free halide perovskite of Cs 3 Sb 2 Cl 9 , magnetic transition metal (Co) was introduced and regulated the Co/Sb bimetallic ratio via a facile co-precipitation method to develop the Cs 4 Co 1.2 Sb 1.8 Cl 12 for light-driven CO 2 conversion. Results of electron paramagnetic resonance (EPR), Kelvin probe force microscopy (KPFM) and theoretical calculations revealed that the introduction of Co 2 + could promote the formation of chlorine vacancies ( V Cl ) and enhance local spin polarization, thereby facilitating CO 2 adsorption and activation, as well as accelerating carriers separation. The average carriers lifetime of the Cs 4 Co 1.2 Sb 1.8 Cl 12 was 1.8 times that of pristine Cs 4 CoSb 2 Cl 12 , beneficial to charges participation in CO 2 reduction reaction. The CO yield from the Cs 4 Co 1.2 Sb 1.8 Cl 12 (130.23 μmol·g −1 ·h −1 ) was 1.33 times that of Cs 4 CoSb 2 Cl 12 and 278 times that of pur e Cs 3 Sb 2 Cl 9 . Notably, without sacrificial agent, an unprecedented CO yield of 66.22 μmol·g −1 ·h −1 was achieved in photocatalytic CO 2 reduction, representing the best performance among lead-free halide double perovskites reported to date. In-situ FTIR analysis demonstrated the carboxylate (COOH*) as the dominated intermediate during CO 2 reduction. This work provides a reference for designing efficient lead-free halide perovskite photocatalysts via enriching halide vacancies and strengthening spin polarization for CO 2 conversion.