Adsorption and Diffusion of H2 in the MOF Type Systems MIL-47(V) and MIL-53(Cr): A Combination of Microcalorimetry and QENS Experiments with Molecular Simulations

Abstract

Quasi-elastic neutron scattering measurements are combined with molecular dynamics simulations to determine the self-diffusivity (Ds) profile of hydrogen in the metal organic framework materials MIL-47(V) and MIL-53(Cr) (MIL, Materials Institut Lavoisier) as a function of loading. Experimentally, a sudden increase in Ds for H2 at low loading (≤1 H2/unit cell) was observed with values at least two orders of magnitude higher than in zeolites. This unusual behavior has been denoted as “super-mobility”. Here, two different force fields available in the literature to represent the H2/H2 and H2/MOF framework interactions have been considered to capture such experimental findings via molecular dynamics simulations. We have shown that (i) a similar magnitude of the energetic contribution for the H2/H2 and H2/MOF framework interactions and (ii) a smoothness of the potential energy surfaces are required in order to match the supermobility of H2 at low loading. The diffusion mechanism at the microscopic scale was su...