An Important Factor Affecting the Supercapacitive Properties of Hydrogenated TiO₂ Nanotube Arrays: Crystal Structure

Employing a suitable crystal structure can significantly modify the electrochemical performances of materials. Herein, hydrogenated TiO₂ nanotube arrays with <001> orientation and different rutile/anatase ratio were fabricated via anodisation, high-temperature annealing and electrochemical hydrogenation. The crystal structure was determined by TEM and X-ray diffraction pattern refinement of whole powder pattern fitting. Combined with the model of anatase to rutile transformation and the characterisation of crystal structure, the effect of phase transition on the super capacitive properties of <001> oriented hydrogenated TiO₂ nanotube arrays was discussed. The results suggested that the anatase grains were characterised by orientation in <001> direction with plate crystallite and stacking vertically to the substrate resulting in excellent properties of electron/ion transport within hydrogenated TiO₂ nanotube arrays. In addition, the specific capacitance of <001> oriented hydrogenated TiO₂ could be further improved from 20.86 to 24.99 mF cm^-2 by the partial rutile/anatase transformation due to the comprehensive effects of lattice disorders and rutile, while the good rate performance and cyclic stability also retained.