Hydrogenated TiO₂ (H-TiO₂) is an efficient photocatalyst for H₂ evolution and useful for the development of a green-energy economy. The role of oxygen vacancies (V_os) in the structure of H-TiO₂ and in the photocatalytic H₂ evolution is the topic of intense debate.

Jun Bao, Song Sun, and colleagues, University of Science and Technology of China, Hefei, using synchrotron facilities, have found that V_os extend from the surface to the bulk phase of TiO₂ during the hydrogenation process and, therefore, contribute to the disorder of H-TiO₂.

V_os introduce defect states that overlap with the conduction band (CB) and lead to a band tail, which results in the visible-light absorption of H-TiO₂. By controlling the hydrogenation degree to restrict the CB tail to just above the H⁺/H₂ redox potential, the most favorable disordered structure for visible-light-driven photocatalytic H₂ evolution can be developed.

• Nature of Conduction Band Tailing in Hydrogenated Titanium Dioxide for Photocatalytic Hydrogen Evolution ,
  Jiawei Xue, Xiaodi Zhu, Yi Zhang, Wendong Wang, Wei Xie, Jilong Zhou, Jun Bao, Ying Luo, Xiang Gao, Yong Wang, Ling-yun Jang, Song Sun, Chen Gao,
  ChemCatChem 2016.
  DOI: 10.1002/cctc.201600237