Molecular Simulation on Hydrogen Storage Capacities of Porous Metal Organic Frameworks

The adsorption equilibrium properties of H2 molecules in various metal-organic frameworks (MOFs) including IRMOF-61, IRMOF-62, and IRMOF-1 were studied using the grand canonical Monte Carlo (GCMC) simulation method with the optimized parameters obtained using the DREIDING force field. The calculated parameters could exactly reproduce the adsorption isotherms of H2 molecules in IRMOF-62. However, they may underestimate the adsorption isotherm of H2 molecules in IRMOF-61 at low pressure. The H2 storage capacities of IRMOF-61 and IRMOF-62 with interpenetrating frameworks were not significantly higher than that of IRMOF1 at room temperature. H2 molecules were preferentially adsorbed near Zn4O units, which were located close to the benzene rings, according to the probability density distribution of H2 molecules in the above MOFs under adsorption equilibrium conditions at 77 K, 100 kPa, and 3.0 MPa. For the MOFs with interpenetrating frameworks, the area with preferential adsorption sites for H2 molecules is smaller and more scattered than the MOF without because of their smaller cavity sizes. The organic linker should be of appropriate length to promote the formation of an interpenetrating framework, which can enhance the interaction between the framework and H2 molecules, and thus improve H2 storage capacity. If the organic linker is too long, it will decrease the adsorption capacity of the MOF for H2 because more corners unable to adsorb H2 are formed.