How many hydrogen molecules (H2) can be stored in a clathrate hydrate cage?

Abstract

Storage of hydrogen gas (H2) in clathrate hydrate at ambient conditions has many potential applications, such as clean energy, environment and ecology protection, submarine, and space rocket. In this research article, the hydrogen gas hydrate is studied by using higher level quantum chemical methods such as MP2, CCSD, and CCSD(T). The interaction energy terms in the hydrate cage and the guest molecular cluster are calculated and analyzed. Some useful conclusion points are summarized as follows: (1) The capacity and stability of the hydrogen molecular clusters in hydrate cages are determined by three energy terms: the hydrogen bond energy (ΔEH-b) of water molecules, the interaction energy (ΔEcage-clst) between the hydrate cage and the guest molecular cluster, and the interaction energy (ΔEclst) of the guest molecular cluster in the cage. (2) The energy term ΔEclst of the hydrogen molecular cluster in the hydrate cage is the only repulsive energy contribution (positive values) to the stability of the gas-hydrate cages, which increases with the number of hydrogen molecules and decreases with the size of the cage volume. (3) The strong hydrogen bond energy ΔEH-b remains constant in a broad range of 2.74 Å to 2.86 Å, in which the change in ΔEH-b is less than ±5 kJmol−1. (4) Capacity of hydrogen molecules in the hydrate cage depends on the volume of the hydrate cages. When the side length RO-O is 2.82 Å, at most 4 hydrogen molecules can be stored in the 512 cage. In large hydrate cages (51262 and 51264), more hydrogen molecules can be stored.