Electrocatalytic and Photoelectrochemical Properties of Nanotubular TiO₂ Electrodes Thermally Treated in Air and Hydrogen

Photoelectrochemical, structural, and electrocatalytic properties of titanium dioxide (TiO₂) nanotubes obtained by the anodization of titanium with subsequent thermal treatment in air or hydrogen were studied. The heat treatment of TiO₂ nanotubes in hydrogen was found to have no effect on the morphology and phase composition of the resultant TiO₂ electrodes. However, such treatment led to a high concentration of defect states in the TiO₂ crystal lattice due to reductive doping accompanied by the conversion of Ti⁴⁺ to Ti³⁺. The rise in the defectivity diminished the overpotential for oxygen electroreduction at an electrode made from titanium dioxide nanotubes annealed in hydrogen compared to such an electrode annealed in air. In addition, annealing in hydrogen led to a significant increase in the long-wavelength photocurrent generated under visible light irradiation.