Electrode distance regulates the anodic growth of titanium dioxide (TiO₂) nanotubes

Electrochemical anodization of titanium has been used widely to produce self-organized TiO₂ nanotube arrays. Many experimental parameters, such as anodizing voltage and electrolyte composition, have been investigated extensively in the anodic growth of TiO₂ nanotubes. The effect of electrode distance on the anodic growth of TiO₂ nanotube arrays, however, remains elusive. This could be an important problem when in situ growth of TiO₂ nanotubes is required in microdevices. Here, we show that decreasing the electrode distance at a constant anodizing voltage enhances the anodic growth of TiO₂ nanotubes and the change of nanotube structures becomes more sensitive to the electrode distance at high voltages. We further demonstrate the correlation between electrode distance and current density during the anodic growth of TiO₂ nanotubes and suggest that the change of current density regulated by electrode distance controls the growth of TiO₂ nanotubes. The present study offers an effective approach to enhance the production of TiO₂ nanotube arrays without changing the anodizing voltage and electrolyte composition and thus provides useful insights to the anodic growth of TiO₂ nanotubes at reduced electrode distances.