Simulation of anodizing current-time curves and morphology evolution of TiO2 nanotube arrays

Through introducing appropriate additives into the electrolytes, the morphology and growth efficiency of TiO₂ nanotube arrays (TNTAs) have been greatly influenced. The anodizing current transients and the corresponding morphology of TNTAs were investigated and compared in detail by SEM. To further understand the mechanism, the measured current-time curves obtained during the anodization of titanium in the electrolytes with different additives are simulated. Notably, in the total anodizing current, the ionic current is separated from the electronic current according to the present model, and that the electronic current and ionic current make different contributions to the growth of TNTAs. It is found that the initiation of nanopores may be caused by the rupture of the oxygen bubbles occluded in the growing oxide, and the opening of nanotubes is thought to be close related to the disturbance effect of the rising bubbles (caused by electronic current). The present results would be helpful for understanding the formation mechanism of TNTAs from the perspective of ionic and electronic current. And practically, the nanotube length can be predicted and deduced quantitatively via simulating and comparing electronic and ionic current.