Volumetric hydrogen sorption capacity of monoliths prepared by mechanical densification of MOF-177

Abstract

Bulk powdered MOF-177 is mechanically compressed to prepare monoliths with bulk densities more than three times its crystallographic density, and their excess and total gravimetric and volumetric hydrogen storage capacities are measured over a pressure range of 0–13 MPa at 77 K and room temperature. The maximum excess volumetric hydrogen storage capacity of these monoliths at ∼6 MPa and 77 K is 25.8 ± 1.2 g L−1, which is a 78% increase of that of powdered bulk MOF-177 and 80% of the theoretical maximum excess volumetric hydrogen storage capacity predicted on the basis of the material's crystallographic density. The monoliths show diminishing excess gravimetric capacity with increasing density which is attributed to their decreasing micropore volume, which in turn stems from the progressive collapse of MOF-177 crystals to an amorphous phase when they are subjected to densification. A modified Dubinin–Astakhov (DA) model is adapted to describe the excess gravimetric adsorption of samples with varying bulk densities. The total volumetric capacity of monoliths prepared from MOF-177 is 48.0 ± 2.1 g L−1 at 13 MPa and 77 K; if a complete storage system that does not reduce this capacity by more than 20% is designed, it can then meet the DOE 2015 volumetric system target at 77 K. Under the same conditions, it is easier to meet the DOE 2015 gravimetric system target of 5.5 wt% as the material's total gravimetric storage capacity is ∼10.3 ± 0.3 wt%.