Boosted Inner Surface Charge Transfer in Perovskite Nanodots@Mesoporous Titania Frameworks for Efficient and Selective Photocatalytic CO 2 Reduction to Methane

Abstract Exploring high‐efficiency and stable halide perovskite‐based photocatalysts for the selective reduction of CO 2 to methane is a challenge because of the intrinsic photo‐ and chemical instability of halide perovskites. In this study, halide perovskites (Cs 3 Bi 2 Br 9 and Cs 2 AgBiBr 6 ) were grown in situ in mesoporous TiO 2 frameworks for an efficient CO 2 reduction. Benchmarked CH 4 production rates of 32.9 and 24.2 μmol g −1 h −1 with selectivities of 88.7 % and 84.2 %, were achieved, respectively, which are better than most reported halide perovskite photocatalysts. Focused ion‐beam sliced‐imaging techniques were used to directly image the hyperdispersed perovskite nanodots confined in mesopores with tunable sizes ranging from 3.8 to 9.9 nm. In situ X‐ray photoelectronic spectroscopy and Kelvin probe force microscopy showed that the built‐in electric field between the perovskite nanodots and mesoporous titania channels efficiently promoted photo‐induced charge transfer. Density functional theory calculations indicate that the high methane selectivity was attributed to the Bi‐adsorption‐mediated hydrogenation of *CO to *HCO that dominates CO desorption.