Photocatalytic Overall Water Splitting over PbTiO₃ Modulated by Oxygen Vacancy and Ferroelectric Polarization

Ferroelectric materials hold great promise in the field of photocatalytic water splitting due to their spontaneous polarization that sets up an inherent internal field for the spatial separation of photogenerated charges. The ferroelectric polarization, however, is generally accompanied by some intrinsic defects, particularly oxygen vacancies, whose impact upon photocatalysis is far from being fully understood and modulated. Here, we have studied the role of oxygen vacancies over the photocatalytic behavior of single-domain PbTiO₃ through a combination of theoretical and experimental viewpoints. Our results indicate that the oxygen vacancies in the negatively polarized facet (001) are active sites for water oxidation into O₂, while the defect-free sites prefer H₂O₂ as the oxidation product. The apparent quantum yield at 435 nm for photocatalytic overall water splitting with PbTiO₃/Rh/Cr₂O₃ is determined to be 0.025%, which is remarkable for single undoped metal oxide-based photocatalysts. Furthermore, the strong correlation among oxygen vacancies, polarization strength, and photocatalytic activity is properly reflected by charge separation conditions in the single-domain PbTiO₃. This work clarifies the crucial role of oxygen vacancies during photocatalytic reactions of PbTiO₃, which provides a useful guide to the design of efficient ferroelectric photocatalysts and their water redox reaction pathways.