The molecular insight into the “Zeolite-ice” as hydrogen storage material

Abstract

“Zeolite-ice” is cavities structure constructed by water molecules that held together by hydrogen-bonds, formed by propane remove from propane hydrate, which structure is similar to zeolite. Hydrogen stored in “Zeolite-ice” is a novel method, which was investigated through experiments and molecular simulations in this paper. Hydrogen storage capacity and the hydrate structures were characterized by Raman spectra. To provide insight into experiments, a series MD simulation had been performed under 250 K–270 K and 30–70 MPa. The results showed that pressure and temperature could influence hydrogen storage performance of propane hydrate. At 270 K, the amount of hydrogen molecules that entered hydrate phase increased with increasing pressure, while hydrogen storage capacity merely fluctuated around 1.0 wt%-1.5 wt% at 260 K and 250 K. Besides, under 60 and 70 MPa, diffusion coefficient of hydrogen molecules at 260 K became relatively low, which led to higher hydrogen capacity than that at 250 K. F4 order parameter analysis and free-energy surface proved that the temperature impacted the stability of cavities of hydrate. This stability caused different motion of hydrogen molecules that doubly occupying large cages. It was feasible to use propane hydrate as a hydrogen storage material and control the pressure and temperature to develop its potential of hydrogen storage.