Enhanced internal field of Bi4NbO8Cl ferroelectric photocatalyst to promote charge separation via constructing crystal plane-dependent BiOI dielectric layer

Spontaneous polarization induced by the unique crystal structure of ferroelectric semiconductor photocatalyst facilitates charge separation and injects new vitality into the improvement of the photocatalytic activity. However, due to the complexity of multi-electric field coupling, the actual efficiency of charge separation driven by the depolarization field is restricted by the shielding field, which is lower than theoretical expectations. Here, we take Bi4NbO8Cl as a model system and selectively construct a BiOI dielectric layer on its positive polarized surface through the adsorption-self-assembly method, aiming to reduce the attenuation of the shielding field to the depolarization field. The enhanced residual depolarization field (RDF) is quantitatively characterized by ferroelectric performance test. Moreover, the charge transfer path and final position are elaborated by photo-deposition experiments, while high-quality interface and calculated difference of the potential between Bi4NbO8Cl and BiOI is responsible for the formation of charge transfer channel. The enhanced RDF promotes the separation of charges, which causes that Bi4NbO8Cl/BiOI photo-degradation of bisphenol A (BPA) gives 7.35-fold greater efficiency than Bi4NbO8Cl. This scheme of weakening the shielding field by surface reconstruction engineering is promising to be extended to more ferroelectric photocatalyst systems.