Simulations of hydrogen gas in clathrate hydrates

In this article, computational studies of hydrogen storage in clathrate hydrate phases are reviewed. A summary of experimental studies of pure hydrogen and binary large guest+hydrogen clathrate hydrate formation are presented in the Introduction. The experimental results include studies of the synthesis conditions, X-ray and neutron diffraction structural characterisations, cage occupancies and guest spectroscopy in these phases. Computational studies of hydrogen clathrate hydrates are categorised in three sections and compared to experiments. In the first section, statistical mechanical, classical molecular dynamics (MD) and Monte Carlo simulations of the hydrogen clathrate hydrate phases are discussed. Many of these studies focus on determining the occupancy of hydrogen in the small- and large-structure II clathrate hydrate phases. In the second section, quantum mechanical studies of the eigenstates of H-2 encapsulated in the clathrate hydrate cages are presented. Ab initio MDs simulations of hydrogen clathrate hydrate phases are also reviewed in this section. In the third section, computational studies of the diffusion of H-2 molecules through the clathrate hydrate cages are reviewed. Diffusion of H-2 guests is an important aspect for the practical use of clathrate hydrates as hydrogen storage materials. The conclusions summarise the insight that molecular simulations have given to the use of clathrate hydrates for hydrogen storage and future directions for hydrogen storage in water-based phases.