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

Bi3TiNbO9, 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 Bi3TiNbO9 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 Bi3TiNbO9 ferroelectric photocatalyst with Rh/Cr2O3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.