Hydrogen Storage in Ti-Decorated BC4N Nanotube

We report an extensive first-principles investigation of a both exohedral and endohedral Ti decorated BC4N nanotube for hydrogen storage. The results reveal that an endohedral capping of Ti is energetically favorable compared to exohedral capping, albeit marginally by similar to 0.1 - 0.4 eV/Ti atom. However, this endohedral insertion process is difficult since it requires overcoming of a rather high energy barrier of similar to 4 eV/Ti atom, as obtained from our nudge elastic band calculation of the minimum energy path. We observe that the exohedral Ti@BC4N can bind up to four hydrogen molecules with successive energies of adsorption lying in the range of similar to 0.4-0.7 eV. We further predict that, at high Ti coverage, the system can absorb up to 5.6 wt % of hydrogen. After establishing the adsorption of hydrogen molecules on the Ti@BC4N nanotube, we have performed molecular dynamics simulation to understand the desorption behavior. It is observed that at 300 K the system remain stable with all four H-2 attached with Ti, while at 500 K hydrogen gets released in molecular form from the Ti@BC4N nanotube without breaking the cage. This investigation underscores the potential of Ti-decorated BC4N nanotube as a promising candidate material for hydrogen storage.