In this work, TiO2 nanotubes were prepared by anodization in ionic liquid at 10 C and 20 C. Different tube diameters (50.8 nm and 70.5 nm) were obtained, and both of them exhibited an anatase phase with distinct crystallite sizes and lattice strains. The increase in the crystallite size led to a decrease in the grain boundary surface area, which could be associated with the recombination centers of the photogenerated charge carriers. Electrochemical impedance spectroscopy was used to correlate the water splitting photoactivity with the charge transfer resistance and the apparent roughness. A schematic representation of the nanotube structures consisting of two layers, compact and porous, proved to be appropriate to clarify the obtained results. (C) 2013 Elsevier B.V. All rights reserved.