Theoretical study of hydrogen adsorption on armchair (5,5) single walled carbon nanotubes

The chemisorption of hydrogen molecule on pristine and Stone-Wales defect armchair (5,5) SWCNTs of cap-ended C₈₀, C₉₀ and open-ended C₇₀H₂₀ has been investigated using density functional theory (DFT) calculations. The adsorption energies of hydrogen molecule on these various SWCNTs of which the structures treated as the flexible and rigid models were obtained at the B3LYP3-21G and B3LYP/6-31G(d) methods and adsorption mechanism were proposed. It was found that adsorption on the SWCNTs as flexible models are stronger than the rigid models. The adsorption energy of hydrogen addition on C-C bond types I, II and III around the Stone-Wales defect area of all the SWCNTs based on the flexible model are hardly different from their pristine SWCNTs. The adsorption energies on the C₁-C₂ bond (type I) are higher than on the C₁-C₃ bond (type II) for the cap-ended C₉₀ and open-ended C₇₀H₂₀. The adsorption on the cap-ended C₈₀ at the C₂-C₄ bond (type III) is higher than on other bond types. In all cases, the adsorption energies on the B-doped SWCNTs are higher than on their corresponding non-doped SWCNTs.