Synergistic effects of heterointerface and surface Br vacancies in ultrathin 2D/2D H2WO4/Cs2AgBiBr6 for efficient CO2 photoreduction to CH4

Efficient photocatalytic conversion of CO2 to CH4 is challenging due to the complex eight-electron coupled proton transfer process. Herein, a 2D/2D H2WO4/Cs2AgBiBr6 (HWO/CABB) heterojunction was fabricated specifically through the “top-down” acid cleavage of layered Bi2WO6 (Bi2O2-WO4) into 2D HWO nanosheet, followed by the in-situ “bottom-up” epitaxial growth of 2D CABB on HWO nanosheet. Detailed characterizations revealed that HWO/CABB possessed abundant surface Br-vacancies (VBr) with an ultrathin 2D/2D heterointerface involving Bi-O and Ag-O bonds, facilitating charge transfer via an S-scheme. Density functional theory (DFT) calculations demonstrated that VBr could promote the adsorption/activation of CO2 and reduce the formation energy barrier of CHO* significantly. Therefore, HWO/CABB exhibited an enhanced CH4 production rate of 22.6 µmol·g−1·h−1 (the electron selectivity of 86.1%), approximately 30 times higher than that of pristine CABB. Furthermore, a plausible mechanism of photocatalytic CO2 to CH4 was proposed based on in-situ diffuse reflectance infrared spectroscopy and DFT calculations. This work demonstrates the potential of heterointerface and surface defects in synergistically tailoring CO2 selective reduction on halide perovskite photocatalysts.