The role of lithium in hydrogen storage in aromatic carbon materials

Three representative aromatic carbon compounds, C₆H₆, C₁₀H₈ and C₁₃H₉, are chosen to simulate H₂ adsorptions in aromatic carbon materials. The calculations of H₂ locating on top of the hexagon center, middle of C-C bond and a C atom of these compounds using density functional and the second order Møller-Plesset perturbation theories indicate that the bindings of H₂ with these compounds are very weak. However, the binding is significantly enhanced when lithium is introduced between the H₂ and the aromatic carbon compound. In particular, the binding energy of H₂ at Li adsorbed on top of the C₁₃H₉ is as large as 2.5 kcal mol^-1, one order of magnitude enhanced. Such a stable H₂ adsorption and the moderate adsorption energy facilitate good H₂ storage. According to the similarity of surface features and chemical reactivities among the various aromatic carbon compounds and carbon nanotubes, we conjecture that the H₂ storage in these materials would all be enhanced by introducing Li. © 2004 Elsevier B.V. All rights reserved.