TiO2 nanotubes have demonstrated perspective applications in the photovoltaic field. They can reduce both the transport dimensionality and the recombination of the photoinjected electrons. In this paper, arrays of TiO2 nanotubes were fabricated by anodization of Ti foils in an ethylene glycol solution containing hydrofluoric acid (HF) under a constant voltage. From field emission scanning electron microscopy (FE-SEM) images, we observed the microstructure Of titania nanotubes. Images show that, as-anodized, the surface of the nanotubes is covered with a precipitate. Ultrasonic treatment was used to remove this precipitate. X-ray diffraction (XRD) results show that the as-anodized amorphous TiO2 nanotubes are converted to crystalline anatase after the samples have been annealed at 500 degrees C during 2 h. Electrochemical behaviour (in terms of charge transfer resistance) was investigated by electrochemical impedance spectroscopy (EIS). The annealed samples were characterized by electrochemical tests. A schematic representation of the TiO2 nanotubes consisting of two layers (i.e. dense and nanoporous) is proposed to explain the obtained results. (C) 2014 Elsevier B.V. All rights reserved.