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The concept of aqueous solution Al-ion battery inspires much enthusiasm in developing a novel chemical power source. In this work, the electrochemical behavior of TiO 2 -NTAs electrode in Al 3+ aqueous solution with different acidity is evaluated. Electrochemical studies showed that both of H + and Al 3+ in aqueous solution are electrochemical active to TiO 2 -NTAs, however, H + is preferential to hydroxylate on the TiO 2 -NTAs surface rather than to intercalate in the TiO 2 -NTAs lattice as compared with Al 3+ under the assistance of Cl − . The surface hydroxylation of TiO 2 -NTAs can retard Al 3+ diffusion in the TiO 2 -NTAs lattice as evidenced by the increase of faradic resistance R F (by EIS) at initial cathodic polarization process, however, the subsequent decrease of R F is due to the conductance improvement of TiO 2 -NTAs with the Al 3+ intercalation. Here it can be concluded that for Al 3+ aqueous solution battery with TiO 2 -NTAs as electrode, the suitable acidity (pH≈3) is required to minimizing the effect of H + . [ABSTRACT FROM AUTHOR]

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]