Facile Formation of Hydrogen Clathrates Using 1,3-Dioxolane in Heavy Water Systems

Hydrogen (H₂) clathrate hydrates offer a promising platform for safe, dense, and reversible H₂ storage, yet require thermodynamic and kinetic enhancement for practical deployment. This study systematically investigates 1,3-dioxolane (DIOX) as a dual-function promoter for structure II (sII) H₂ hydrates formed in D₂O. Systematic variation of formation conditions, which includes pressure (9.5–12.5 MPa), temperature (274.65–276.65 K), and DIOX concentration (3.56–6.56 mol %), revealed that 5.56 mol % DIOX at 275.65 K and 12.5 MPa achieved optimal performance, with H₂ uptake reaching 30.49 ± 0.68 v/v (∼0.24 wt %) within 2 h, marking a benchmark for binary hydrate systems under mild conditions. While D₂O is known to yield slightly more stable hydrates than H₂O due to stronger O–D bonds, its impact in H₂-DIOX systems remains largely unexplored. This work bridges that gap by experimentally examining isotopic effects on hydrate phase stability, cage dynamics, and Raman spectral behavior, providing new insights into promoter–solvent interactions and hydrate lattice evolution. Thermodynamic equilibrium boundaries revealed the lowest formation pressure (∼1.1 MPa at 275.5 K) for the optimal formulation. P-XRD confirmed pure sII lattice formation, and in situ Raman spectroscopy validated selective cage occupancy, with DIOX in large 5¹²6⁴ cages and H₂ in small 5¹² cages. The findings highlight the ability of DIOX-D₂O system to reduce formation thresholds and accelerate hydrate kinetics without compromising capacity. Thus, the H₂-DIOX-D₂O system exhibits the essential traits for clean and safe H₂ storage under practical conditions, supporting future integration into energy infrastructure.