Search

Abstract: 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 120bar 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 (∼80,000bar) are required to completely fill the MOF pores with H2 at 298K. Nevertheless, much lower pressures (several 100bar) are sufficient to attain the H2 storage targets for MOFs with large free volumes. For IRMOF-16 with a large free volume (4.322cm3/g), only modest pressures (170 and 280bar) 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. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen storage and delivery in eight representative metal–organic frameworks (MOFs) was investigated using grand canonical Monte Carlo (GCMC) simulations. The simulations demonstrate that the optimal isosteric heat of adsorption (Q st) for maximum hydrogen delivery using MOFs is approximately 20kJ/mol. The results also suggest that increasing the Q st for MOFs with large surface areas (>4800m2/g) is required to attain current hydrogen storage targets in terms of deliverable capacity. [Copyright &y& Elsevier]

Highlights: [•] Calculated hydrogen Maxwell–Stefan diffusivity in Mg-functionalized MOFs. [•] Highlighted relationship between hydrogen heat of adsorption and M–S diffusivity. [•] Showed M–S diffusivity decreases exponentially with increasing heat of adsorption. [•] Lessons from this study can be applied to diffusion in other host/guest systems. [ABSTRACT FROM AUTHOR]

Abstract: Grand canonical Monte Carlo simulations were used to calculate hydrogen adsorption in IRMOF-16, NU-100, and UiO-68 functionalized with Mg or Fe catecholates on the linkers. We examined how altering the number of metal catecholate groups affects H2 uptake and deliverable capacity near ambient temperature. We find that large free volume and an isosteric heat of adsorption (Q st) of 20kJmol−1 at low loading will maximize gravimetric deliverable capacity while a small pore diameter will maximize volumetric deliverable capacity. This suggests a trade-off between the properties that lead to maximal gravimetric and volumetric capacities. For example, our calculations suggest that NU-100 functionalized with six Fe catecholate groups per linker takes up 5.5wt.% deliverable H2 at 243K and 100bar, but only 24.2gL−1 deliverable H2. [Copyright &y& Elsevier]