A long-standing polarized electric field in TiO₂@BaTiO₃/CdS nanocomposite for effective photocatalytic hydrogen evolution

Ferroelectrics have the advantage of spatially separating the photogenerated charge carriers via the spontaneous polarized electric field, although the strength of the polarized electric field may suffer from the influence of the electrostatic shielding effect, which could reduce the charge carrier separation without mechanical stress. Herein, we developed a novel CdS decorated TiO₂@BaTiO₃ core–shell nanocomposite, where the optimal ratio of TiO₂, BaTiO₃ and CdS are 53.43, 37.37 and 9.20 wt%, respectively, for the best photocatalytic activity. The TiO₂@BaTiO₃/CdS nanocomposite reported in this work offers a persistent electric field in the ferroelectric BaTiO₃ shell, due to the limited shielding effect in an asymmetrically polarized field. With the built-in electric field as the driving force, the photogenerated electrons and holes flowed into the CdS surface and the TiO₂ core, respectively, with improved charge separation to participate in water-splitting reactions. The measured charge carrier lifetime of TiO₂@BaTiO₃/CdS nanocomposite via transient fluorescence spectrum is 0.42 ns, which is much longer than the TiO₂ (0.25 ns) and TiO₂@BaTiO₃ (0.31 ns) samples. The TiO₂@BaTiO₃/CdS nanocomposite shows an enhanced photocatalytic hydrogen evolution rate of 13.22 mmol/g∙h under visible light illumination with an AQE of 52.50 % at 405 nm monochromatic light. This is much better than their components and binary composites, including TiO₂/Pt (0.63 mmol/g∙h), CdS (1.23 mmol/g∙h), TiO₂@BaTiO₃ (0.03 mmol/g∙h), TiO₂/CdS (0.53 mmol/g∙h), and BaTiO₃/CdS (2.62 mmol/g∙h). This work provides an effective strategy for the construction of a ferroelectric photocatalyst with much-improved charge separation by the permanent internal electric field.