The titanium dioxide nanotube array (TiO2-NTA) is prepared by a two-step anodic oxidation method and annealed at 450 degrees C subsequently. The Al-inserted TiO2-NTA is prepared by polarizing the TiO2-NTAs electrode at 0.4 mA for 2 min in 1 mol/L AlCl3. The results show that the Al-inserted sample still remains pure anatase TiO2 phase (by XRD) and keeps intact nanotube array structure (by FE-SEM). The X-ray photoelectron spectroscopy (XPS) analysis indicates that the insertion of Al3+ into TiO2-NTAs facilitates in the reduction of Ti4+ to Ti3+. Electrochemical investigation on the Al3+ insertion process reveals that presence of ions plays vital role for the effective insertion and de-insertion of Al3+ into/from the TiO2-NTA. (C) 2014 Elsevier Ltd. All rights reserved.