title: Hydrogen storage in molecular compounds.
abstract: At low temperature (T) and high pressure (P), gas molecules can be held in ice cages to form crystalline molecular compounds that may have application for energy storage. We synthesized a hydrogen clathrate hydrate, H(2)(H(2)O)(2), that holds 50 g/liter hydrogen by volume or 5.3 wt %. The clathrate, synthesized at 200-300 MPa and 240-249 K, can be preserved to ambient P at 77 K. The stored hydrogen is released when the clathrate is warmed to 140 K at ambient P. Low T also stabilizes other molecular compounds containing large amounts of molecular hydrogen, although not to ambient P, e.g., the stability field for H(2)(H(2)O) filled ice (11.2 wt % molecular hydrogen) is extended from 2,300 MPa at 300 K to 600 MPa at 190 K, and that for (H(2))(4)CH(4) (33.4 wt % molecular hydrogen) is extended from 5,000 MPa at 300 K to 200 MPa at 77 K. These unique characteristics show the potential of developing low-T molecular crystalline compounds as a new means for hydrogen storage.
authors.affiliation: Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA. wmao@uchicago.edu
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao