Bimetallic B-Site Halide Perovskites for Enhanced Photocatalytic CO₂ Reduction

Artificial photosynthesis by the capturing and conversion of CO2 to value-added fuels is an attractive avenue to solve the greenhouse effect and energy crisis issues. In the recent decade, lead halide perovskites (HPs) have evoked considerable interest in the photocatalysis field, particularly for CO2 reduction. However, their inherent toxicity toward the environment and human health greatly restricts their practical applications, prompting the search for lead-free alternatives with excellent optoelectronic traits and catalytic performance. Herein, a series of all-inorganic bimetallic mixed HPs Cs3Sb2–yBiyCl4Br5 (0 ≤ y ≤ 2) was developed and studied for CO2 photoreduction. Among the samples with varying bismuth and antimony compositions, Cs3Sb0.5Bi1.5Cl4Br5 (CSBX-1.5) demonstrated the best photocatalytic performance, with a CH4 yield of 6.28 μmol g–1 under visible-light irradiation (λ ≥ 410 nm) for 6 h and a continuous supply of humidified CO2 gas flow. Computational studies revealed the effect of B-site metal incorporation toward the Br p-band center, where charge delocalization around the active halogen site was notably enriched for greater CO2 adsorption and activation. Experimental characterization and photoelectrochemical studies further uncovered the narrower bandgap, higher reduction potential, prolonged charge carrier lifetime, and lower electron–hole recombination of CSBX-1.5. This work provides insights into the bimetallic approach for enhanced photocatalytic performance of lead-free HPs and elucidates the tuning of their optoelectronic properties for robust band structure tailoring.