Ab initio mechanistic insights into the stability, diffusion and storage capacity of sI clathrate hydrate containing hydrogen

Abstract

Gas hydrates are non-conventional materials offering great potential in capturing, storage, and sequestration of different gases. The weak van der Waals interactions between a gas molecule and the pore walls stabilize these non-stoichiometric structures. The present article reports an ab initio improved van der Waals density functional (vdW-DF2) study devoted to the interactions associated with H 2 , CH 4 , and CO 2 adsorption in sI clathrate hydrate. The study provides the clathrate stability, diffusion, and energy storage of possible mixed gas occupancy in sI cages in the presence of H 2 . The results also provided the hydrogen energy landscapes and the estimated diffusion activation energy barriers to the large and small cage to be 0.181 and 0.685 eV, respectively. In addition, the results showed that the presence of CH 4 or CO 2 could enhance the storage capacity, thermodynamic stability, and hydrogen diffusion in sI clathrates. The volumetric storage, gravimetric storage, and molecular hydrogen content in H 2 –CH 4 binary sI clathrate are calculated to be 2.0 kW h/kg, and 1.8 kW h/L, and 5.0 wt%, respectively. These results are comparable to DOE targets of hydrogen storage. • CH 4 works as a thermodynamic promoter to stabilize clathrate for hydrogen storage. • Clathrate stability is improved by a double occupancy (H 2 –CO 2 ) of the large cage. • Double occupancy of the large cages facilitates H 2 diffusion. • H 2 –CH 4 sI clathrate energy storage can reach 2.0 kWh/kg and 1.8 kWh/L. • H 2 –CH 4 sI estimated capacity can meet DOE targets of volumetric and gravimetric energy storage.