To evaluate the total usable capacity of H2 for the materials under practical operational conditions, we calculated the total H2 uptake, which can be defined as the sum of the adsorbed H2 and the amount of free H2 in the pore-i.e., the product of pore volume and bulk H2 density at the storage condition (Figures ). The usable capacity is obtained by subtracting the total uptake at the discharge condition from that at the charging condition (Table ). Significantly, the volumetric usable capacities for Cu I M-MFU-4l are comparable to or slightly lower than that for ZnCl-MFU-4l. We reason that the amount of H2 that is weakly physisorbed and located within the void space of the frameworks is 4-6 times greater than the H2 uptake originating from the Cu I sites in a Cu I M-MFU-4l framework because the number of the Cu I sites is much lower than that of weak adsorption sites even though the fraction of the usable weak adsorption sites may not be high.