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Applied Physics A, 2013
Shigeru Ishikawa, Tokio Yamabe
Department of Chemistry, Faculty of Science, Tokai University, 4-1-1 Kitakaname, Hiratsuka, 259-1292, Japan and
Nagasaki Institute of Applied Science, 536 Aba-machi, Nagasaki, 851-0193, Japan.
Abstract
We evaluated the adsorption energy of a hydrogen molecule in nanocarbons consisting of graphene sheets. The nanocarbon shapes were a pair of disks with separation 2d, a cylinder with radius d, and a truncated sphere with radius d. We obtained the adsorption energy in the form of a 10–4 Lennard–Jones function with respect to 1/d. The values of the potential depth (D) and equilibrium distance (de), respectively, were 94 meV and 2.89 Å for the disk pair, 158 meV and 3.14 Å for the cylinder, and 203 meV and 3.37 Å for the sphere. When d=d e, the adsorption energy of the disk pair (cylinder) became deeper than −0.9D, and it approached −D when the radius (length) increased to more than twice its separation (radius). The adsorption energy of the sphere was increased from −D to −0.5Dwhen the radius of the opening increased from 0 to d e. These results suggest that porous carbon materials can increase the adsorption energy by up to ∼200 meV if the carbon atoms are arranged on a spherical-like surface with ∼7 Å separation. This may lead to practical hydrogen storage for fuel cells.
Figure Legend
Potential energy curves of a hydrogen molecule adsorbed by nanocarbons with different shape and size. The potential depth (D) and spacing (de) parameters are respectively 94 meV and 2.89 Å for the disk pair, 158 meV and 3.14 Å for the cylinder, and 203 meV and 3.37 Å for the sphere.
