Hydrogen hydrate cage occupancy: A key parameter for hydrogen storage and transport

In this work, an accurate model is presented for predicting the hydrogen hydrate cage occupancies. This novel predictive method is based on the hydrate phase stability and hydrogen effective molecular size and configuration. The hydrogen-hydrogen interactions in a hydrate cage are calculated using the Kihara potential and the pairwise additivity rule. The accuracy and reliability of the proposed method are evaluated by comparison with various literature data. The model shows that the small cage double occupancy of structure II is possible if the volume expansion of the cages has been taken into account and a slight change in the volume of small cages leads to a considerable decrease in pressure required for double occupancy of small cages. The model also indicates that the large cages volume expansion has a weaker effect on the required pressure for quadruple occupancy in comparison with the case of double occupancy of small cages. The proposed model confirms the findings of most of the previous experimental observations and theoretical simulations.