Molecular insight into hydrogen storage in clathrate hydrates

Abstract

Hydrate-based H2 storage is based on the mechanism of trapping H2 in water-based structures that are environmentally friendly and cost-efficient. Understanding the effects of common promoters on hydrate-based H2 storage at the molecular level is crucial for designing efficient storage systems, and for discovering novel promoters. Here, a series of μs-scale molecular dynamics simulations are performed to investigate the nucleation of binary H2 hydrates from gas-liquid two-phase solutions in the presence of various promoters, i.e., CH4, CO2, C2H6, C3H8, C5H10, and THF. The simulation results indicate that the H2 and promoter molecules first dissolve in water from the gas phase and then are absorbed on the cage-faces, promoting the nucleation and growth of binary H2 hydrates. THF is the most effective promoter for hydrate-based H2 storage, exhibiting high performance in converting H2 from the gas phase to hydrates. It is followed by CH4, C2H6, and CO2; C3H8 and C5H10 molecules are less effective H2 hydrate promoters. The presence of large promoter molecules enhances multi-occupied cage formation. The molecular insight into the nucleation of binary H2 hydrates with various promoters provided here not only contributes to a broader understanding of hydrate-based H2 storage but is expected to motivate further experimental and computational studies.