Kinetic analysis of the anodic growth of TiO₂ nanotubes: Effects of voltage and temperature

Considering the widespread applications of TiO₂ nanotube arrays in industry, we study the anodic growth of TiO₂ nanotube arrays in an organic electrolyte consisting of water, NH₄F, and ethylene glycol in the temperature range of 30 to 60 °C and in the voltage range of 30 to 50 V. The kinetic analysis reveals that the dominant mechanism controlling the growth of the TiO₂ nanotubes is "field-induced dissolution". The temperature dependence of the growth rates for the nanotube length and diameter follows the Arrhenius relationship. The activation energy for the length growth of the TiO₂ nanotubes is much larger than that for the diameter growth, and is a linearly decreasing function of the anodization voltage. A power law relationship between the growth rate for the nanotube length and the anodization voltage is used to describe the length growth of the TiO₂ nanotubes at steady state, which is supported by the experimental results. The diffraction patterns obtained from the fast Fourier transform analysis of the SEM images of the TiO₂ nanotube arrays reveal the narrow-spatial distribution of the TiO₂ nanotubes.