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Center for Nonlinear Studies |
One of the most crucial issues to be resolved before hydrogen can be established as the “energy carrier” of the future, especially in the sector of transportation, is storage. Among the technologies that have been developed in this direction, storage in solid materials seems to be an attractive solution. A wide range of materials have been investigated for their hydrogen storage capacity. Some of them are: hydrides, porous structures of carbon, metal-organic frameworks (MOFs), and recently inclusion compounds (gas hydrates) that are of interest to this presentation.
Hydrogen storage in nanoporous solid materials involves physical adsorption of hydrogen on the solid surface. Consequently, the amount of adsorbed hydrogen increases with the specific area of the material. Hydrogen remains in molecular form and is bonded on the solid surface via Van der Waals-type interactions. For this reason, adsorption of hydrogen is completely reversible and hydrogen can be released by slightly heating the material.
Clathrate hydrates are ice-like crystalline materials. They comprise a special kind of nanoporous materials and mainly consist of water. The lattice of the water molecules contains cavities (pores of diameter 0.7-1.2 nm) where small guest molecules can be entrapped (“enclathrated”). There are three common types of hydrates, namely sI, sII and sH, depending on their crystallographic structure. The stability of these materials originates from the interactions between the entrapped guest molecules and the water lattice, and consequently, hydrates are not stable in the absence of the guest molecule.
Since the geometry of their crystal is known, the formation of gas hydrates can be simulated as a process of gas adsorption in a porous material. For this reason, Grand Canonical Monte Carlo (GCMC) simulations seem to be an effective method for studying hydrates as a complementary approach to the classical Thermodynamics. In this work, the implementation of GCMC in the study of hydrates is presented and an overview of the results of several cases examined is given. First, argon hydrates and He-THF binary hydrates are considered in order to examine issues related to the multiple occupancy of cavities. Next, we proceed to the case of hydrogen hydrates. Several cases of pure hydrogen, as well as binary hydrogen hydrates are examined. In general, the results from our GCMC simulations are in good agreement with other available data in literature, either experimental or theoretical. Conclusions drawn from this study on hydrogen hydrates can be useful for the evaluation of the hydrogen storage capacity of hydrates.
Although research in gas hydrates as a hydrogen storage material is in a very early stage, these materials seem very interesting because they store hydrogen in a completely reversible manner, they are inexpensive and environmentally friendly.
Host: Panagiotis Maniadis