Self-ordered Nanotubular TiO₂ Multilayers for High-Performance Photocatalysts and Supercapacitors

Arrays of multilayered TiO₂ nanotubes are successfully fabricated by anodizing commercial Ti foils with multi-pulsed voltage waveforms. The fabricated structures feature an interesting multilayered morphology with each layer consisting of self-ordered TiO₂ nanotubes (diameter of tens of nanometers and length of several hundred nanometers) aligned vertically to the Ti substrate, and the possible growth mechanism is proposed. The novel multilayered TiO₂ nanotubes exhibit significantly enhanced photocatalytic efficiency than the conventional TiO₂ nanotubes and the multilayered nanoporous TiO₂ structures previously reported by our group. Moreover, the multilayered TiO₂ nanotubes are for the first time investigated for supercapacitor applications, enabling superior capacitance and good cycling stability: the specific capacitance of the C-modified multilayered TiO₂ nanotubes is ∼60 times higher than the pristine multilayered TiO₂ nanotubes, and ∼1.6 times of the C-modified single-layered TiO₂ nanotubes.