Hydrogen storage via clathrate hydrates under mild conditions enabled by mixed cyclic ether synergy

Abstract

Hydrogen (H₂) storage via clathrate hydrates represents a compelling strategy for sustainable energy solutions. However, slow formation kinetics and rigorous thermodynamic conditions pose significant barriers to their widespread implementation. Here, we present a molecularly tailored approach using mixed cyclic ether promoters, 1,3-dioxane (DXN) and 1,3-dioxolane (DIOX), in deuterium oxide (D₂O) to significantly enhance H₂ storage under mild, and practically relevant conditions. We tasted H₂ enclathration across various parameters, including promoter ratios, formation temperatures, promoter concentrations, multiple reformation cycles, and initial H₂ pressures. Our optimized formulation 2DXN-1DIOX (5.56 mol%) achieves superior H₂ uptake of 43.77 43.77 ± 2.68 mmol H₂/mol D₂O at 274.45 K and 12.5 MPa, which reproducibly increases to 56.12 ± 0.58 mmol H₂/mol D₂O at 18.5 MPa, driven by structural and kinetic synergy between DXN and DIOX molecules. Powder X-ray diffraction confirmed the formation of structure II (sII) hydrates, while Raman spectroscopy elucidated molecular-level details of structural heterogeneity, revealing how promoter-induced lattice flexibility enhances H₂ diffusion and promotes efficient hydrate cage accessibility within the hydrate framework. Complementary thermodynamic phase equilibrium investigations established that the mixed-promoter system considerably expands the hydrate stability envelope toward milder pressures and temperatures, further highlighting its potential. Collectively, this work reveals how mixed cyclic ether promoters synergistically enhance H₂ enclathration and hydrate stability under practical conditions, thereby providing a molecular design framework to advance clathrate-based H₂ storage toward commercial viability.