Observation of Interstitial Molecular Hydrogen in Clathrate Hydrates

• Published in: Angewandte Chemie International Edition Vol. 53; no. 40; pp. 10710 - 10713
• Main Authors: Grim, R. Gary, Barnes, Brian C., Lafond, Patrick G., Kockelmann, Winfred A., Keen, David A., Soper, Alan K., Hiratsuka, Masaki, Yasuoka, Kenji, Koh, Carolyn A., Sum, Amadeu K.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 26-09-2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alloys; Cages; Clathrate hydrates; Crystal lattices; density functional calculations; Hydrates; Hydrogen storage; inclusion compounds; Interstices; Interstitials; molecular dynamics; neutron diffraction; Pictures; Position (location); Raman spectroscopy; density functional calculations; neutron diffraction; inclusion compounds; Raman spectroscopy; molecular dynamics
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201406546

The current knowledge and description of guest molecules within clathrate hydrates only accounts for occupancy within regular polyhedral water cages. Experimental measurements and simulations, examining the tert‐butylamine+H2+H2O hydrate system, now suggest that H2 can also be incorporated within hydrate crystal structures by occupying interstitial sites, that is, locations other than the interior of regular polyhedral water cages. Specifically, H2 is found within the shared heptagonal faces of the large (43596273) cage and in cavities formed from the disruption of smaller (4454) water cages. The ability of H2 to occupy these interstitial sites and fluctuate position in the crystal lattice demonstrates the dynamic behavior of H2 in solids and reveals new insight into guest–guest and guest–host interactions in clathrate hydrates, with potential implications in increasing overall energy storage properties.
Breaking the boundaries: In the presence of molecular hydrogen, interstitial occupancy is observed in the type VI clathrate hydrate (see picture; tBuNH2 in interstices (red) with H2 (green)). This observation revises the definition of clathrate hydrate guest occupancy that assumes all guests are contained within the interior of the host water lattice.