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.