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.