The interaction of the H2 molecule with a graphene layer and with a small-radius carbon nanotube was investigated using ab initio density functional methods. The H2 could interact with carbon materials such as graphene, graphite and nanotubes either through physisorption or chemisorption. The physisorption mechanism involved the binding of the hydrogen molecule on the material as a result of weak van der Waals forces, while the chemisorption mechanism involved the dissociation of the hydrogen molecule and the ensuing reaction of both hydrogen atoms with the unsaturated C-C bonds to form C-H bonds. In the calculations, account was taken of van der Waals interactions using a method based upon the concept of maximally localized Wannier functions. Several adsorption sites and orientations of the hydrogen molecule relative to the carbon surface were explored and the associated binding energies and adsorption potentials were computed. Much weaker adsorption, than for graphene, characterized the physisorption interaction of the H2 molecule with a small-radius (2,2) carbon nanotube. The barriers for H2 dissociation on the nanotube external surface were significantly lower, with respect to graphene; reflecting the marked effect of the substrate curvature in promoting hydrogen dissociation.

Physisorption, Diffusion, and Chemisorption Pathways of H2 Molecule on Graphene and on (2,2) Carbon Nanotube by First Principles Calculations. F.Costanzo, P.L.Silvestrelli, F.Ancilotto: Journal of Chemical Theory and Computation, 2012, 8[4], 1288-94