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Transition‐metal‐ion doping is an effective method to shorten bandgap and enhance visible‐light absorption of TiO 2 , but there are still some serious challenges for most doping technologies, such as nonuniform doping, severe lattice damages, metal atoms agglomeration, and inactivated impurities. Herein, a simple and universal hydrothermal method is developed to realize the effective transition‐metal ions doping of TiO 2 (including Fe, Co, Mn, Cu, V, and Cr). The photoelectrochemical water splitting performances of Cr‐doped TiO 2 nanorods with multifarious Cr ion valence states (Cr 3+ or Cr 6+ ions), various Cr‐ion concentrations, with or without oxygen vacancy activation are emphatically and systematically studied. Experiments and theoretical calculations demonstrate that the remarkably enhanced carrier separation and injection efficiencies are the key factors to improve the visible‐light photoactivity, benefiting from the homogeneous distribution of impurity atoms and the incorporation of oxygen vacancies. The Cr 3+ ‐ion‐doped TiO 2 nanorod arrays with oxygen vacancy activation (Cr 3+ /O v –TiO 2 ) displays an impressive incident photon‐to‐electron conversion efficiency of 5.4% at 450 nm visible light, far superior to the pure TiO 2 of 0.03%. Furthermore, no obvious photocurrent decay is observed in the Cr 3+ /O v –TiO 2 photoanode after 12 h continuous light illumination.
Chen et al. (Thu,) studied this question.