Titania nanotubes from pulse anodization of titanium foils

A pulse waveform for the anodic growth of TiO2 nanotube arrays is described. The arrays were grown on Ti foil substrate using a 20 V/−4 V pulse sequence in NH4F electrolyte in neat water or glycerol containing 1% water. The pulse anodization approach yielded superior nanotube morphology and photocurrent response (in Na2SO4 supporting electrolyte) relative to samples grown via the conventional, continuous anodization method. Further, the results from this study provide crucial supporting evidence for mechanistic models of anodic growth and self-assembly of oxide nanotube arrays on the parent metal surface. Specifically, adsorption of NH4+ species on the TiO2 surface that is promoted by the negative voltage pulse is shown to ameliorate the extent of chemical attack of the growing oxide nanoarchitecture by the electrolyte F− species, resulting in better nanotube morphology.