The~potential~of~hydrogen~storage~in~hydrate~and~graphitic~systems

Many methods have been proposed for efficient storage of molecular$^{ }$hydrogen for fuel cell applications. Recently, it was found that molecular hydrogen can be stored in large quantity approaching the U.S. Department of Energy goals of$^{ }$6.5{\%} mass ratio in ice clathrate under high pressure and low temperature [1]. Attempts were made to increase the stability of the clathrate. Unfortunately, so far the modified hydrates failed to meet the elusive goal [2,3]. To understand the thermodynamic stability and storage capacity, hydrogen occupancy in clathrate hydrate was examined with a statistical$^{ }$mechanical model in conjunction with first-principles quantum$^{ }$chemistry calculations [4]. The theoretical approach is extended to graphitic systems [5]. It is shown that insufficiently accurate $^{ }$carbon--H$_{2}$ interaction potentials, together with the neglect$^{ }$and incomplete treatment of the quantum effects in previous$^{ }$theoretical investigations led to incorrect conclusions for$^{ }$the absorption capacity. A proper account of the contribution$^{ }$of quantum effects to the free energy and the equilibrium constant$^{ }$for hydrogen adsorption suggest that the U.S. Department of$^{ }$Energy specification can be approached in a graphite-based physisorption$^{ }$system. [1] W.L. Mao, H.-K. Mao, A.F. Goncharov, V.V. Struzhkin,$^{ }$Q Guo, Q., \textit{et al}. \textit{Science} 297, 2247--2249 (2002) [2] H. Lee, J. Lee, D.Y. Kim, J. Park, Y. Seo, H. Zeng, I.L. Moudrakovski, C.I. Ratcliffe, J.A. Ripmeester, \textit{Nature} 434, 743-746, (2005) [3] L.J. Florusse, C.J. Peters, J. Schoonman, K.C. Hester, C.A. Koh, S.F. Dec, K.N. Marsh, E. D. Sloan, \textit{Science}, 306, 469 -- 471 (2004) [4] S. Patchkovskii, J.S. Tse, \textit{Proc. Nat. Acad. Sci}., 100, 14645-14650 (2003) [5] S. Patchkovskii, J.S. Tse, S.N. Yurchenko, L. Zhechkov, T. Heine, G. Seifert, \textit{Proc. Nat. Acad. Sci}., 102, 10439-10444 (2005)