Self-ordering electrochemistry: a review on growth and functionality of TiO₂ nanotubes and other self-aligned MO_x structures

Among all one dimensional nanostructures other than carbon, titania nanotubes have gained increasingly more scientific interest due to a successful combination of functional material properties with a well controllable nano-architecture. For self-organized TiO₂ nanotube arrays not only the simple increase in the specific surface area but also their self-aligned nature leads to a significant enhancement of the performance when used in photoelectrochemistry, photocatalysis, dye-sensitized solar cells, or electrochromic devices. In addition to this, these ordered and size-controlled nanostructured TiO₂ surfaces also have material-specific advantages, for example in superhydrophobic/superhydrophilic and biomedical applications. The formation of these vertically oriented nanotube arrays can be achieved by a simple one-step electrochemical self-assembly process. By adjusting the anodization parameters, the geometry such as the tube length or diameter can easily be controlled. The present review addresses the formation, properties and applications not only of TiO₂ nanotubes but also of related transition metal oxides.