Thermodynamic limits on hydrogen storage in sodalite framework materials: a molecular mechanics investigation

Porous, crystalline solids, built up from TO4 (T = Al, Si, Ge, P) tetrahedra, are potentially attractive materials for the safe storage of significant amounts of hydrogen. In this study we concentrate on the large void volume sodalite framework type and investigate the effect of incrementally increasing the molecular hydrogen loading in the constituent cages. A range of H2 cage filling arrangements is explicitly considered and for each their energetic effect on the system is assessed using energy minimisation calculations with suitably parameterised interatomic potentials. The results of the calculations indicate how the hydrogen storage capacity is linked to the T-atom types and cation content and their occupancy in the framework. Considering hydrogen storage as a weight percentage, the maximum loading capacity of all sodalite materials was found to be moderately high (≈4.8 wt.%) but also relatively invariant of framework constitution due to the counterbalancing effect of increased adsorption capacity with heavier framework atoms.