Gradient tungsten-doped Bi3TiNbO9 ferroelectric photocatalysts with additional built-in electric field for efficient overall water splitting

Bi 3 TiNbO 9 , a layered ferroelectric photocatalyst, exhibits great potential for overall water splitting through efficient intralayer separation of photogenerated carriers motivated by a depolarization field along the in-plane a -axis. However, the poor interlayer transport of carriers along the out-of-plane c -axis, caused by the significant potential barrier between layers, leads to a high probability of carrier recombination and consequently results in low photocatalytic activity. Here, we have developed an efficient photocatalyst consisting of Bi 3 TiNbO 9 nanosheets with a gradient tungsten (W) doping along the c -axis. This results in the generation of an additional electric field along the c -axis and simultaneously enhances the magnitude of depolarization field within the layers along the a -axis due to strengthened structural distortion. The combination of the built-in field along the c -axis and polarization along the a -axis can effectively facilitate the anisotropic migration of photogenerated electrons and holes to the basal {001} surface and lateral {110} surface of the nanosheets, respectively, enabling desirable spatial separation of carriers. Hence, the W-doped Bi 3 TiNbO 9 ferroelectric photocatalyst with Rh/Cr 2 O 3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.