Boosting CO2 photoreduction with Ta doped Bi4NbO8Cl via polarization induced charge separation.

Photocatalytic CO2 reduction offers an environmentally friendly and promising strategy for CO2 utilization under mild conditions. However, the efficient separation of photogenerated charge carriers remains a critical challenge that directly influences catalytic performance. In recent years, polarization field engineering has emerged as a novel and effective approach to enhancing charge separation efficiency. Herein, we synthesized Ta, Sb, and V doped Bi4NbO8Cl (Bi4NbO8Cl-Ta/Sb/V) photocatalysts via the molten salt method. By partially substituting Nb in the NbO6 octahedra with different metal elements, the local charge distribution was modulated, inducing a polarization field that enhanced charge separation and transfer, thereby significantly improving photocatalytic CO2 reduction performance. As a result, Bi4NbO8Cl-5 %Ta exhibited outstanding CO and CH4 production rates of 0.24 μmol/(g·h) and 0.03 μmol/(g·h) in pure water, showing 12 and 1.9 fold enhancements compared to pristine Bi4NbO8Cl. Photoelectrochemical characterizations confirmed that Ta doping effectively promoted charge separation and transfer. Piezoelectric force microscopy (PFM) measurements reveal an enhanced piezoelectric response in Bi4NbO8Cl-5 %Ta compared to Bi4NbO8Cl, verifying the formation of a polarization electric field that significantly promotes charge carrier separation. Furthermore, in situ Fourier Transform infrared spectroscopy (in situ FTIR) detected key reaction intermediates, including *COOH, *CO, *CHO, and *OCH3, providing direct evidence for the reaction pathway and mechanism of CO2 reduction to CO and CH4. This work provides novel insights and theoretical guidance for designing efficient CO2 conversion photocatalysts through polarization field modulation to achieve efficient charge separation.