Rapid anodic growth of TiO2 and WO3 nanotubes in fluoride free electrolytes

In the present work we report on the formation of bundles of high aspect ratio TiO2 nanotubes and WO3 nanopores structures with very thin tube or pore walls using anodization under “high voltage” conditions in perchlorate or chloride containing electrolytes. The bundles of TiO2 nanotubes consist of separated tubes with diameters in the range of approximately 20–40 nm and the WO3 nanopores consist of pores with diameters in the range of 30–50 nm. Growth occurs locally at specific surface locations. Both the TiO2 and the WO3 structures can be grown up to several dozens of micrometers in length within few minutes. We suggest that the growth of these high aspect structures is initiated by localized anodic breakdown event, triggered by a sufficiently high applied anodic field.