The electrochemical behavior of Cl− assisted Al3+ insertion into titanium dioxide nanotube arrays in aqueous solution for aluminum ion batteries.

The titanium dioxide nanotube array (TiO 2 -NTA) is prepared by a two-step anodic oxidation method and annealed at 450 ∘ C subsequently. The Al-inserted TiO 2 -NTA is prepared by polarizing the TiO 2 -NTAs electrode at 0.4 mA for 2 min in 1 mol/L AlCl 3 . The results show that the Al-inserted sample still remains pure anatase TiO 2 phase (by XRD) and keeps intact nanotube array structure (by FE-SEM). The X-ray photoelectron spectroscopy (XPS) analysis indicates that the insertion of Al 3+ into TiO 2 -NTAs facilitates in the reduction of Ti 4+ to Ti 3+ . Electrochemical investigation on the Al 3+ insertion process reveals that presence of Cl − ions plays vital role for the effective insertion and de-insertion of Al 3+ into/from the TiO 2 -NTA. [ABSTRACT FROM AUTHOR]