(494e) Investigation of Tuning Effect By Tetrahydrofuran (THF) in THF-H2 Hydrates Via Molecular Dynamics Simulations

Hydrogen (H₂) is regarded as a clean energy due to its high energy density (~141.86 MJ/Kg) and zero emission of carbon dioxide. Clathrate hydrates, which are composed by three-dimensional network of hydrogen bonding of water, are numerously studied as hydrogen storage media because of their simple synthetic strategies. Pure H₂ hydrates require extremely harsh formation conditions, thermodynamic promoters such as tetrahydrofuran (THF) or cyclopentane (CP) were introduced to change the formation conditions to be milder. However, the thermodynamic promoters reduce maximal storage capacity, because they stabilize the hydrate structure by occupying 5¹²6⁴ cage of the hydrates. To overcome the drawback of the thermodynamic promoter, tuning effect, which small guest molecules stabilize the large cage of the hydrates instead of the thermodynamic promoter, was widely studied to increase the storage capacity of the hydrates. However, the origin of tuning effect has not been understood at molecular-level until now. Here, we investigated the tuning effect of THF-H₂ hydrates by all-atomic molecular dynamics simulations for the first time.¹ Before the MD simulation, off-diagonal Lennard-Jones parameter between H₂ and water was optimized by high-level ab-initio calculations. With the optimized parameter, phase equilibria of the THF-H₂ hydrates were measured by MD simulations. Thereafter, the growth of the THF-H₂ hydrates with respect to molar concentration of THF and pressure was observed and analyzed by 1 microsecond MD simulations.