Hydrogen in Porous Tetrahydrofuran Clathrate Hydrate

• Published in: Chemphyschem Vol. 9; no. 9; pp. 1331 - 1337
• Main Authors: Mulder, Fokko M., Wagemaker, Marnix, van Eijck, Lambert, Kearley, Gordon J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 23.06.2008; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; clathrates; Colloidal state and disperse state; density functional calculations; Exact sciences and technology; General and physical chemistry; hydrogen storage; neutron diffraction; NMR spectroscopy; Porous materials; clathrates; density functional calculations; Hydrogen storage; Density functional; Neutron diffraction; Hydrogen; Clathrate; Calculation; NMR spectrometry; NMR spectroscopy; Porous material; Hydrates
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200700833

The lack of practical methods for hydrogen storage is still a major bottleneck in the realization of an energy economy based on hydrogen as energy carrier.1 Storage within solid‐state clathrate hydrates,2–4 and in the clathrate hydrate of tetrahydrofuran (THF), has been recently reported.5, 6 In the latter case, stabilization by THF is claimed to reduce the operation pressure by several orders of magnitude close to room temperature. Here, we apply in situ neutron diffraction to show that—in contrast to previous reports[5, 6]—hydrogen (deuterium) occupies the small cages of the clathrate hydrate only to 30 % (at 274 K and 90.5 bar). Such a D2 load is equivalent to 0.27 wt. % of stored H2. In addition, we show that a surplus of D2O results in the formation of additional D2O ice Ih instead of in the production of sub‐stoichiometric clathrate that is stabilized by loaded hydrogen (as was reported in ref. 6). Structure‐refinement studies show that [D8]THF is dynamically disordered, while it fills each of the large cages of [D8]THF⋅17D2O stoichiometrically. Our results show that the clathrate hydrate takes up hydrogen rapidly at pressures between 60 and 90 bar (at about 270 K). At temperatures above ≈220 K, the H‐storage characteristics of the clathrate hydrate have similarities with those of surface‐adsorption materials, such as nanoporous zeolites and metal–organic frameworks,7, 8 but at lower temperatures, the adsorption rates slow down because of reduced D2 diffusion between the small cages. Hydrogen storage in the clathrate of tetrahydrofuran (THF) and water (see picture) is studied by using in situ neutron diffraction. The results indicate a moderate hydrogen uptake. Rapid hydrogen diffusion through the material is observed at temperatures between 220 and 270 K. Phase separation between ice and the stoichiometric clathrate occurs at low THF concentrations.