Enhancement of Hydrogen Sorption on Metal(Ni, Rh, Pd) Functionalized Carbon Nanotubes: a DFT Study

Hydrogen interacted with pristine single-walled carbon nanotubes(SWNTs) and single/dimer metal doped ones(M-CNTs) was investigated via density functional theory(DFT) simulations. The most stable configurations of Ni, Rh, Pd on SWNTs were identified. The interaction of H-2 molecules with pristine SWNTs and M-CNTs was investigated. The results show that H-2 molecules can be adsorbed on the pristine SWNTs via a weak physical interaction, which is much weaker than those of H-2 molecules with M-CNTs by chemisorption. Each Ni, Rh and Pd doped SWNTs can respectively chemisorb three, two, or one H-2 molecules and the H-H bond of H-2 molecule is elongated. Furthermore, the H-2 molecule could be dissociated owing to the presence of the Ni-Ni bond for Ni dimer doped SWNT, forming new Ni-H bonds. While such a dissociation could not be observed on RH2/Pd-2-CNT samples. Density of state(DOS) results show that the s orbital of hydrogen can hybridize with the d orbital of metal atom, resulting in the stronger inteaction between H-2 and M-CNTs, impying that the hydrogen storage capacity could be enhanced in the presence of M-CNTs. The comparison of the interaction mechanism among different metals doped CNTs can screen out the most effective hydrogen-adsorption materials and the design of the related materials by computational approaches.