Boosting visible-light-driven catalytic hydrogen evolution via surface Ti3+ and bulk oxygen vacancies in urchin-like hollow black TiO2 decorated with RuO2 and Pt dual cocatalysts

TiO2-Based photocatalysts with hollow structure have attracted much attention owing to their low density, scattering effect and slow photon effect. However, the wide bandgap (E-g = 3.2 eV) and high recombination rate of photogenerated charges hinder their practical application. Herein, a novel hollow urchin-like black RuO2/TiO2/Pt photocatalyst with surface Ti3+ and bulk single-electron oxygen vacancies (Vo center dot) due to self-doping is reported for visible-light photocatalytic activity. Space-separated dual cocatalysts (RuO2 and Pt NPs) with redox capability can greatly improve the separation efficiency of photogenerated electrons and holes of TiO2. Furthermore, constructing surface Ti3+ and bulk Vo center dot in TiO2 is considered an efficient approach for narrowing bandgap and enhancing the visible-light absorption. In particular, the surface Ti3+ promotes a self-hydrogenated shell to reduce the activation barrier of H-2, which enhances the hydrogen evolution. However, excessive bulk Vo center dot as carrier recombination centers are not conducive to the hydrogen production. Positron annihilation lifetime spectra (PALS) indicated that the concentration ratio of surface Ti3+ and bulk Vo center dot is a key factor for efficient photocatalytic hydrogen evolution. The synergy between the spatially separated dual cocatalysts and optimum surface Ti3+/bulk Vo center dot ratio greatly increases the activity of the catalyst under visible light.