Volumetric Hydrogen Storage Capacity in Metal-Organic Frameworks

Molecular hydrogen storage in metal-organic frameworks (MOFs) is one possibility for on-board storage in fuel-cell vehicles, but so far generally only the gravimetric hydrogen storage capacity has been considered. Here we analyze the volumetric absolute hydrogen uptake of many MOFs measured at 77 K and 2.0-2.5 MPa in our laboratory in recent years and correlate these to their structure. A linear relation is found for the volumetric absolute hydrogen uptake as a function of the volumetric surface area, which yields the same hydrogen surface density as in Chahine's rule. Furthermore, the experimental data show a correlation between the specific volume and the specific surface area, which is used to develop a phenomenological model for the volumetric absolute uptake as a function of the gravimetric absolute uptake. Most of the MOFs follow this relation. However, the interpenetrated framework, CFA-7, shows the strongest deviation and the highest volumetric absolute hydrogen storage capacity at 77 K and 2.0 MPa.