Probing hydrogen adsorption behaviors of Ti- and Ni-decorated carbon nanotube by density functional theory

The hydrogen adsorption properties of Ti and Ni atoms as media on single-walled carbon nanotube (SWCNT) have been studied by density functional theory (DFT) incorporating a pragmatic method to correctly describe van der Waals interactions. The results show that both Ti and Ni atoms can reliably adhere to single-walled carbon nanotube, respectively, making strong TM-C bonds. Meantime, it is found that the average adsorption energies of H-2 by Ti and Ni atoms are decreased with the increase of the amount of H-2 adsorption. Ti or Ni atoms can bind up to no more than six H-2 molecules on a carbon nanotube. It is inferred that these transition metals (TMs) can adsorb molecular hydrogen through likely Kubas-type interaction. By comparing the interaction energies among TM and H atoms, it can be identified that the hydrogen adsorption properties of Ti atoms are superior to those of Ni atoms at certain conditions. The present investigation is useful in the wider development of carbon-based nanomaterials as potential high-capacity H-2 storage media.