An investigation on formation and electrochemical capacitance of anodized titania nanotubes

The mechanism of titania nanotubes formation and growth during anodization of titanium in NH4F/ethylene glycol electrolyte at 45 V applied voltage was investigated using field emission scanning electron microscopy (FESEM). The initial stage of the anodization occurs with the formation of a compact oxide layer with nanoscale pits. With the increase of anodization time, the pits transform to larger and deeper pores due to the integration of the smaller and larger pores, finally creating self-ordered titania nanotubes. The porous structure increases electrochemical capacitance from 18.3 μF cm−2 for 10 s anodization time to 49.9 μF cm−2 for 1800 s anodization time. The cyclic voltammetry (CV) transforms from a near symmetry rectangular shape to x-axis symmetry with higher current density as the anodization time increases due to increased specific surface area of the nanotubular structure. The larger CV size at more cathodic regions is characteristics of the n-type behaviour of titania materials, as also shown in the Mott–Schottky analysis.