Enhancement of hydrogen sorption on metal(Ni, Rh, Pd) functionalized carbon nanotubes: a DFT study

Abstract

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 configura-tions of Ni, Rh, Pd on SWNTs were identified. The interaction of H2 molecules with pristine SWNTs and M-CNTs was investigated. The results show that H2 molecules can be adsorbed on the pristine SWNTs via a weak physical in-teraction, which is much weaker than those of H2 molecules with M-CNTs by chemisorption. Each Ni, Rh and Pd doped SWNTs can respectively chemisorb three, two, or one H2 molecules and the H―H bond of H2 molecule is elongated. Furthermore, the H2 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/Pd2-CNT samples. Density of state(DOS) results show that the s orbital of hydrogen can hybridize with the d orbital of metal atom, re-sulting in the stronger inteaction between H2 and M-CNTs, impying that the hydrogen storage capacity could be en-hanced 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.