Lead-Free Halide Perovskite Cs₂AgBiBr₆/Bismuthene Composites for Improved CH₄ Production in Photocatalytic CO₂ Reduction

CO₂ photocatalytic conversion into value-added fuels through solar energy is a promising way of storing renewable energy while simultaneously reducing the concentration of CO₂ in the atmosphere. Lead-based halide perovskites have recently shown great potential in various applications such as solar cells, optoelectronics, and photocatalysis. Even though they show high performance, the high toxicity of Pb²⁺ along with poor stability under ambient conditions restrains the application of these materials in photocatalysis. In this respect, we developed an in situ assembly strategy to fabricate the lead-free double perovskite Cs₂AgBiBr₆ on a 2D bismuthene nanosheet prepared by a ligand-assisted reprecipitation method for a liquid-phase CO₂ photocatalytic reduction reaction. The composite improved the production and selectivity of the eight-electron CH₄ pathway compared with the two-electron CO pathway, storing more of the light energy harvested by the photocatalyst. The Cs₂AgBiBr₆/bismuthene composite shows a photocatalytic activity of 1.49(±0.16) μmol g^-1 h^-1 CH₄, 0.67(±0.14) μmol g^-1 h^-1 CO, and 0.75(±0.20) μmol g^-1 h^-1 H₂, with a CH₄ selectivity of 81(±1)% on an electron basis with 1 sun. The improved performance is attributed to the enhanced charge separation and suppressed electron-hole recombination due to good interfacial contact between the perovskite and bismuthene promoted by the synthesis method.