Ab initio study of the molecular hydrogen occupancy in pure H2 and binary H2-THF clathrate hydrates

Abstract

The hydrogen storage capacity in the clathrate hydrate was studied by ab initio calculations and ab initio molecular dynamics simulations. Thermodynamic and kinetic analysis shows that the cage occupancy in small and large cages is affected by each other, and THF has a stabilization effect on the hydrate structure. For pure H2 hydrates, small cages can be occupied by single H2 molecule or double H2 molecules, while the corresponding occupancy in large cages is four or three H2 molecules, resulting in a hydrogen storage capacity of ∼3.8 wt% and ∼4.4 wt%, respectively. For binary H2-THF hydrates, small cages are likely to be singly occupied with H2, but large cages can simultaneously accommodate one H2 molecule and one THF molecule. The hydrogen storage capacity falls in between ∼1.6 wt% and ∼3.8 wt%. This study highlights the importance of the clathrate hydrates as a hydrogen storage material and also is helpful to understand the controversy about the hydrogen storage capacity in the clathrate structure.