Structures, electronic properties, and hydrogen-storage capacity of single-walled TiO2 nanotubes

Structural and electronic properties of single-walled TiO2 nanotubes were investigated using density-functional theory. The strain energies were computed as a function of tube diameter and the small-sized nanotubes are less stable than the large-diameter ones. All TiO2 nanotubes are semiconductors with indirect bandgaps independent of the tube chirality. The bandgaps of those nanotubes slightly increase with increase in tube diameter, and they are higher than that of the bulk TiO2 solid. The hydrogen-storage capacity for a selected TiO2 nanotube is 3.2 wt% with the binding energy of 0.05 eV per H2 molecule.