Regulating Oxygen Vacancies and Fermi Level of Mesoporous CeO2‐x for Intensified Built‐In Electric Field and Boosted Charge Separation of Cs3Bi2Br9/CeO2‐x S‐Scheme Heterojunction

Abstract Regulating the built‐in electric field (BEF) in the heterojunction is is a great challenge in developing high‐efficiency photocatalysts. Herein, by tailoring the content of oxygen vacancies in the constituent reduction semiconductor (mesoporous CeO 2‐x ), a precise Fermi level (E F ) regulation of CeO 2‐x is realized, yielding an amplified E F gap and intensified BEF in the Cs 3 Bi 2 Br 9 perovskite quantum dots/CeO 2‐x S‐scheme heterojunction. Such an enhanced BEF offers a strong driving force for directional electron transfer, boosting charge separation in the S‐scheme heterojunction. As a result, the optimized Cs 3 Bi 2 Br 9 /CeO 2‐x heterojunction delivers a remarkable CO 2 conversion efficiency, with an impressive CO production rate of 80.26 µmol g −1 h −1 and a high selectivity of 97.6%. The S‐scheme charge transfer mode is corroborated comprehensively by density functional theory (DFT) calculations, in situ X‐ray photoelectron spectroscopy (XPS), and photo‐irradiated Kelvin probe force microscopy (KPFM). Moreover, diffuse reflectance infrared Fourier transform spectra (DRIFTS) and theoretical calculations are conducted cooperatively to reveal the CO 2 photoreduction pathway.