Optimization of Hydrogen Hydrate Formation Kineticsthrough Molecular Coupling of 1,3-Dioxane and l‑Leucine

Hydrogen (H₂) is increasingly acquiring recognition as a critical energy vector for a low-carbon and sustainable future due to its high gravimetric energy density and zero emissions of pollutants upon combustion. Solidified hydrogen storage (Solid-HyStore) via clathrate hydrates form presents substantial advantages, such as the requirement for only moderate pressures and temperatures compared to compressed H₂ storage and lower energy demands relative to liquid H₂ storage. However, the inherently sluggish kinetics of H₂ hydrate formation remain a significant barrier in hydrate based H₂ storage endeavors. In this study, we introduce an environmentally benign dual-function promoter possessing both thermodynamic and kinetic features, 1,3-dioxane, and couple it with an auxiliary kinetic copromoter, l-leucine. A unique synergy between 1,3-dioxane and l-leucine was exploited in stepping up H₂ hydrate formation kinetics. Process parameters during hydrate evolution were optimized by conducting experiments at different temperatures of 270.65, 272.65, and 274.15 K, pressures of 6.5, 9.5, 12.5, and 15.5 MPa, and solution volumes of 10, 20, and 30 mL. An optimal volumetric H₂ uptake of 39.25(±1.23) v/v and <i>T</i>₉₀ = 199(±44.66) min was achieved using 1,3-dioxane at a 5.56 mol % stoichiometric concentration combined with 1.0 wt % l-leucine, at 272.65 K, 12.5 MPa, and 10 mL. Additionally, p-XRD analysis confirmed the formation of a structure II (sII) hydrate with characteristic diffraction patterns matching theoretical crystallographic data, validating the structural framework of the H₂-1,3-dioxane hydrate system. Raman spectroscopy further substantiated the molecular arrangement by revealing H₂ occupation in the small cages and 1,3-dioxane’s preferential occupancy of the large cages within the sII hydrate lattice. This work is a crucial step in the development of Solid-HyStore technology, leveraging the properties of mixed H₂-1,3-dioxane hydrate.