Molecular simulations of very high pressure hydrogen storage using metal–organic frameworks

Hydrogen adsorption isotherms in 20 metal–organic frameworks (MOFs) were obtained from grand canonical Monte Carlo simulations and used to develop quantitative correlations to quickly estimate the H2 uptake of MOFs at 120 bar from the free volume of the adsorbent. These correlations were then verified with a diverse set of 22 MOFs that were not used in developing the correlations. The simulated high-pressure H2 isotherms in five representative MOFs show that extremely high pressures (∼80,000 bar) are required to completely fill the MOF pores with H2 at 298 K. Nevertheless, much lower pressures (several 100 bar) are sufficient to attain the H2 storage targets for MOFs with large free volumes. For IRMOF-16 with a large free volume (4.322 cm3/g), only modest pressures (170 and 280 bar) are required to achieve the 2010 and 2015 gravimetric targets. However, considerably higher pressures are required for attaining the volumetric targets. In addition, three interesting pressure regions, which are observed in the H2 densities within the MOFs (ρad) up to very high pressures, are analyzed by radial distribution functions between the adsorbed H2 molecules as well as those between H2 molecules and metal corners.