Self-organized and uniform TiO2 nanotube arrays with optimized NH4F concentration in electrolyte by high voltage electrochemical anodization

Abstract

Large diameter and ordered TiO2 nanotubes (NTs) were fast fabricated in an electrolyte containing lactic acid and ethylene glycol with different amount of NH4F at various high anodization voltages up to 220 V. In this work, we could optimize F− ionic concentration in the electrolyte at each anodization voltage and the uniform films without any oxide breakdown were successfully achieved. The optimum NH4F concentration at which NTs can be formed homogeneously, decreases with the increment of anodization voltage. As a result, the fastest mean growth rate of 2.45 μm min−1 was attained in 0.075 M NH4F at 150 V. Growth rate of TiO2 nanotubes is explained taking into account the role of F− ions and their limited diffusion through TiO2 nanotubes from bulk electrolyte. The interpore distance of the nanotubes is increased with enhanced anodization voltage.