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 Cs₃Sb_2-yBi_yCl₄Br₅ (0 ≤ y ≤ 2) was developed and studied for CO₂ photoreduction. Among the samples with varying bismuth and antimony compositions, Cs₃Sb_0.5Bi_1.5Cl₄Br₅ (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.