Kinetics of titania nanotube formation by anodization of titanium films

We report the kinetics of titania nanotube length evolution during anodization of titanium films. Our results show that the nanotube length increase is thermally activated, and governed by voltage-dependent activation energy 0.6 eV ≤ Eeff ≤ 1.1 eV expressed by Eeff = E0-αVanod where α is a constant and E0 = 1.6 eV is a voltage-independent term. The proximity of E0 to that of oxygen diffusion in titania suggests that oxygen transport across the titania walls at the pore bottoms is the rate-limiting step. These results provide insights into the mechanism of titania nanotube formation and a framework for their rational synthesis for applications.