A promoted photocatalysis system trade-off between thermodynamic and kinetic via hierarchical distribution dual-defects for efficient H-2 evolution

The tradeoff between thermodynamic and kinetic factors in a photocatalytic system to enhance its activity is still a challenging issue. The modificatin of a photocatalyst with defects provides an effective way to adjust the light absorption properties, but it may lead to the loss of kinetic factors. Herein, a strategy of constructing dual-defects is demonstrated to address this challenge. Bulk N doping and surface oxygen vacancies are introduced into black TiO2 nanotube array in hierarchies through the introduction of N source during anodization process and secondary aluminothermic reduction, respectively. The co-existing of dual-defects reduces the band-gap through p orbital modulation, and the constant conduction band position ensures the preservation of thermodynamic capabilities. Moreover, a built-in electric field is formed owing to the different electrical properties between hierarchical distributions of dual-defects, which establishes the channels for efficient charge transfer. The thermodynamic and kinetic factors of the tradeoff are realized by the broadening of light absorption induced by "correct concentration " of dual-defects and the acceleration of photogenerated charge transfer induced by "correct distribution " of dual-defects, respectively. As a result, the hierarchically modified black TiO2 exhibits robust hydrogen evolution activity of 3183 mu mol.g(-1).h(-1), roughly a 21-fold improvement with respect to pristine TiO2 under visible light illumination.