Probing the pathway of H2-THF and H2-DIOX sII hydrates formation: Implication on hydrate-based H2 storage

Hydrogen (H2) 2 ) is recognized as a promising energy carrier for the future world, owing to its high energy density and zero carbon emissions. H2 2 storage in the form of solidified hydrates represents an emerging economic-viable and eco-friendly technology for large-scale application. Thermodynamic hydrate promoters (THPs) enhanced H2 2 hydrate formation at mild pressure conditions by forming sII or sH hydrates. However, the formation pathway and promotion mechanism of H2-THP 2-THP sII hydrates are yet to be elucidated. In this study, the composition of H2- 2- THF/H2-DIOX 2-DIOX sII hydrates was analyzed in both 5.56 mol% THF and DIOX systems by high-pressure mu-DSC. The well-designed kinetic experiments coupled with morphology observation were conducted to reveal the key stage for H2-THF/H2-DIOX 2-THF/H 2-DIOX hydrates formation at pressures from 8.3 MPa to 18.3 MPa. Moreover, Raman spectroscopy was employed to validate the proposed formation pathway and the cage occupancy ratio of H2 2 and THP molecules. Both pure THP hydrates and H2-THP 2-THP hydrates were identified by high-pressure mu-DSC. Formation of H2- 2- THP sII hydrates requires a specific condition that both H2 2 and THP molecules simultaneously occupy the small and large cages of sII hydrates for 5.56 mol% THP. Based on the Raman spectroscopy, the ratio of H2 2 molecules in the 5 12 small cages to THP molecules in the 5 12 6 4 large cages increased with pressure. The experimental results contribute to a fundamental understanding of the role of THP in promoting H2-THP 2-THP hydrate formation. The findings guide the adoption of effective THPs with optimal concentrations and contact patterns for hydrate-based H2 2 storage technology.