The storage of large quantities of hydrogen at safe pressures1 is a key factor in establishing a hydrogen-based economy. Previous strategies—where hydrogen has been bound chemically2, adsorbed in materials with permanent void space3 or stored in hybrid materials that combine these elements3—have problems arising from either technical considerations or materials cost2,3,4,5. A recently reported6,7,8 clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (∼ 2 kbar) required to produce the material make it impractical. The synthesis pressure can be decreased by filling the larger cavity with tetrahydrofuran (THF) to stabilize the material9, but the potential storage capacity of the material is compromised with this approach. Here we report that hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to ∼4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability. The tuning mechanism is quite general and convenient, using water-soluble hydrate promoters and various small gaseous guests.
This work was supported by the Korea Research Foundation and the Brain Korea 21 Project.
Describes the additional information on the experimental methods of XRD and Raman spectroscopy to obtain the structural information and identify the molecular behaviour of H2 in hydrate cages.
Contains three Supplementary Figures. Figure S1 shows the powder XRD pattern for the double hydrate. Supplementary Figure S2 shows the phase behaviour of the double hydrate for 5.56 mol% THF concentration. As it can be seen in Supplementary Figure S3, the effect of the extinction coefficient in this study can be treated as a constant value regardless of THF concentrations.
This table shows the powder XRD patterns of THF + H2 double hydrate. Indexed results show that the formed structure of THF + H2 double hydrate is sII hydrate.