The storage of large quantities of hydrogen at safe pressures is a key factor in establishing a hydrogen-based economy. Previous strategies--where hydrogen has been bound chemically, adsorbed in materials with permanent void space or stored in hybrid materials that combine these elements--have problems arising from either technical considerations or materials cost. A recently reported clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (approximately 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 material, 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 approximately 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.

The inhibition activities of two antifreeze proteins (AFPs) on the formation of tetrahydrofuran (THF) clathrate hydrate have been tested. AFPs from fish (wfAFP) and insect (CfAFP) changed the morphology of growing THF hydrate crystals. Also, both AFPs showed higher activities in inhibiting the formation THF hydrate than a commercial kinetic inhibitor, poly(vinylpyrrolidone) (PVP). Strikingly, both AFPs also showed the ability to eliminate the "memory effect" in which the crystallization of hydrate occurs more quickly after the initial formation. This is the first report of molecules that can inhibit the memory effect. Since the homogeneous nucleation temperature for THF hydrate was measured to be 237 K, close to that observed for ice itself, the action of kinetic inhibitors must involve heterogeneous nucleation. On the basis of our results, we postulate a mechanism for heterogeneous nucleation, the memory effect and its elimination by antifreeze proteins.

The critical nanoaggregate concentration (CNAC) of asphaltenes in toluene has been studied by a variety of methods recently. Here, we explore low-frequency electrical impedance measurements to detect and quantify nanoaggregate formation of asphaltenes. The Nyquist and Bode plots confirm the frequency range necessary for the dominance of (organic) ion conduction as opposed to reactive impedance. Impedance measurements are made as a function of the asphaltene concentration in toluene. We perform ionic conduction measurements at low frequency to avoid electrode polarization effects and then extrapolate to obtain direct-current (DC) conductivity. In a plot of DC conductivity versus asphaltene concentration, we see a clear break between two linear regions that is attributed to nanoaggregate formation. Very close agreement with high-Q ultrasonic measurements is shown for two petroleum asphaltenes with different CNACs. In addition, this work is shown to be consistent with previous alternating-current (AC) conductivity measurements. Measurements on aqueous salt solutions are used to validate measurements of the mole fraction of asphaltenes ionized in toluene, which is ∼10 -5 . The plausible identity of these ions is discussed. A comparison of conductivity at concentrations below and above CNAC indicates that the aggregation number is small (<10) in agreement with previous findings. Resin shows no aggregation and is also much less conductive than asphaltenes. We also observe a break in the slope at higher asphaltene concentrations, where nanoaggregate clustering has been observed.