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

Abstract

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·) 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· 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 H₂, which enhances the hydrogen evolution. However, excessive bulk Vo· 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· is a key factor for efficient photocatalytic hydrogen evolution. The synergy between the spatially separated dual cocatalysts and optimum surface Ti³⁺/bulk Vo· ratio greatly increases the activity of the catalyst under visible light.