Water oxidation sites located at the interface of Pt/SrTiO3 for photocatalytic overall water splitting

When a proton reduction cocatalyst is loaded on an n-type semiconductor for photocatalytic overall water splitting (POWS), the location of water oxidation sites is generally considered at the surface of the semiconductor due to upward band-bending of n-type semiconductor which may ease the transfer of the photogenerated holes to the surface. However, this is not the case for Pt/SrTiO3, a model semiconductor based photocatalyst for POWS. It was found that the photogenerated holes are more readily accumulated at the interface between Pt cocatalyst and SrTiO3 photocatalyst as probed by photo-oxidative deposition of PbO2, indicating that the water oxidation sites are located at the interface between Pt and SrTiO3. Electron paramagnetic resonance and scanning transmission electron microscope studies suggest that the interfacial oxygen atoms between Pt and SrTiO3 in Pt/SrTiO3 after POWS are more readily lost to form oxygen vacancies upon vacuum heat treatment, regardless of Pt loading by photodeposition or impregnation methods, which may serve as additional support for the location of the active sites for water oxidation at the interface. Density functional theory calculations also suggest that the oxygen evolution reaction more readily occurs at the interfacial sites with the lowest overpotential. These experimental and theoretical studies reveal that the more active sites for water oxidation are located at the interface between Pt and SrTiO3, rather than on the surface of SrTiO3. Hence, the tailor design and control of the interfacial properties are extremely important for the achievement or improvement of the POWS on cocatalyst loaded semiconductor photocatalyst.