Leucine-Enhanced sII Hydrate Kinetics for Hydrogen Storage

Hydrogen (H 2 ) is increasingly recognized as a key component in the transition to a low-carbon, sustainable future, thanks to its high energy density and clean combustion, which produce no pollutants or greenhouse gases. Storing H 2 in solid-hydrate form (Solid-HyStore) offers significant advantages, including the ability to operate at moderate pressures and temperatures, unlike compressed H 2 storage, and lower energy consumption compared to liquid H 2 storage. However, the slow kinetics of H 2 hydrate formation present a significant barrier to the large-scale adoption of this storage method. In this study, we introduce l -leucine, an environmentally benign kinetic promoter, in combination with the thermodynamic promoter, 1,3-dioxolane (DIOX), to accelerate the kinetics of hydrogen hydrate formation. Our research focuses on the influence of l -leucine on mixed H 2 -DIOX hydrates, examining both the kinetics and morphology of hydrate formation. We found that the optimal combination of 1.0 wt % l -leucine with 5.56 mol % DIOX significantly enhances hydrate formation, achieving a maximum volumetric hydrogen uptake of 34.40 (±1.86) v/v at 270.5 K and 12.5 MPa. Notably, the time required to reach 90% of the maximum hydrogen uptake ( t 90 ) was drastically reduced from 804.33 min in pure DIOX to 194.67 min with the inclusion of 1.0 wt % l -leucine. Structural confirmation via Raman spectroscopy revealed that DIOX molecules consistently occupy the 5 12 6 4 cages of the sII hydrate, while hydrogen is enclathrated in the smaller 5 12 cages, supporting the cage occupancy pattern of the mixed H 2 -DIOX hydrates. Our study also highlights the importance of compounding driving forces such as initial pressures, gas–liquid ratios, and thermodynamic promoter (DIOX) concentrations in determining a more favorable environment for hydrate nucleation and growth and the overall kinetics of mixed H 2 -DIOX hydrate formation. Insights gained in this study offer the potential of strategic promoter combinations to overcome kinetic limitations, thereby advancing the feasibility of hydrate-based hydrogen storage.