In situ Blue titania via band shape engineering for exceptional solar H₂ production in rutile TiO₂

Designing an excellent solar photocatalyst based on TiO₂ without an external cocatalyst such as Pt remains unresolved despite its exceptional potential for renewable energy production. Here, we report a state-of-the-art solar-driven photocatalytic Cl-doped rutile TiO₂, in nanosheet morphology with (110) facets, for H₂ production from water splitting in the absence of any external cocatalyst. The Cl-doped rutile TiO₂ nanosheets are easily synthesised via a layered titanate's interconversion through a simple dilute HCl treatment and thermal heating at a convenient temperature. We demonstrate that engineering the band shape can result in long-lasting photogenerated Ti³⁺, which subsequently can act as an in situ cocatalyst in rutile TiO₂. According to our density functional calculations, the Cl dopant has a pivotal role in improving the band shape of TiO₂, i.e., significantly reducing the effective mass of the photogenerated electrons and holes, especially when compared to the effect of oxygen vacancy. Consequently, the boosted carrier mobility, resulting from lighter carriers, photogenerates a significant number of prolonged Ti³⁺ species that enhance photocatalytic activity in situ (i.e., in situ blue titania). Our results show that despite the considerable efforts that have been directed towards narrowing TiO₂’s band gap, band shape engineering offers a more facile and robust solution for photocatalysis.