The relationship between the growth rate of anodic TiO2 nanotubes, the fluoride concentration and the electronic current

•The growth rate of nanotubes is directly related to the anodizing current.•The growth rate of nanotubes is not directly related to the fluoride ion concentration.•Addition of H3BO3 to the electrolyte reduces the anodizing current and growth rate.•Borate can restrain fluoride ions from entering into the contaminated layer.