Black Anatase TiO₂ Nanotubes with Tunable Orientation for High Performance Supercapacitors

Black TiO₂ is a versatile material that finds many applications in the field of photocatalysis but also in energy storage devices, such as supercapacitors. In this work, a new method is developed for the synthesis of black TiO₂ in the form of nanotubes. Amorphous TiO₂ nanotubes (TNTs) are annealed and reduced in the presence of CaH2, and by a simple manipulation, we are able to obtain control over the preferred crystal orientation. The reduced TNTs show high power and energy densities, as well as unprecedented stability under intensive charge/discharge cycling. The oriented reduced TNTs show metallic-like behavior with improved conductivity when compared to the polycrystalline analogue. This work contributes to the development of highly robust and efficient oxides for electrode material in supercapacitors.