Toward understanding of hydrogen storage in single-walled carbon nanotubes by investigations of chemisorption mechanism

Abstract

We provide an overview of experimental and theoretical studies on hydrogen storage in single-walled carbon nanotubes (SWNTs) via chemisorption mechanism. The atomic hydrogens that are generated by dissociation of H2molecules bind with carbon atoms of nanotubes, leading to strong C-H bonds in the chemisorption process. Recent experimental study indicates that 5.1∈±∈1.2 wt% hydrogen storage could be achieved by hydrogenation (chemisorption process) of SWNTs. Our computational study shows that chemisorptions of one and two hydrogen atoms on the external surface of (3, 3), (4, 4), (5, 5), and (6, 6) armchair SWNTs are highly exothermic processes. Furthermore, two hydrogen atoms favor to bind at adjacent positions rather than at alternate carbon sites. This is different from the results reported on zigzag nanotubes. The chemisorptions of one and two hydrogen atoms significantly alter the C-C bond lengths of SWNTs in the vicinity of hydrogen addition due to the change of hybridization of carbon atom(s) from sp2to sp3at the chemisorption site(s). The effect of increasing the length of SWNTs on the geometries and the reaction energies of hydrogen chemisorption has also been explored. The high exothermicity of the chemisorption of hydrogen atoms on the surface of SWNTs explains the reason for the requirement of high temperature to remove hydrogen from hydrogenated SWNTs. © 2010 Springer Science+Business Media B.V.