Theoretical Limits of Hydrogen Storage in Metal-Organic Frameworks: Opportunities and Trade-offs

Because of their high surface areas, crystallinity, and tunable properties,metal−organic frameworks (MOFs) have attracted intense interest as next-generationmaterials for gas capture and storage. While much effort has been devoted to thediscovery of new MOFs, a vast catalog of existing MOFs resides within the CambridgeStructural Database (CSD), many of whose gas uptake properties have not beenassessed. Here we employ data mining and automated structure analysis to identify,“cleanup,” and rapidly predict the hydrogen storage properties of these compounds.Approximately 20 000 candidate compounds were generated from the CSD using analgorithm that removes solvent/guest molecules. These compounds were thencharacterized with respect to their surface area and porosity. Employing the empiricalrelationship between excess H2 uptake and surface area, we predict the theoretical total hydrogen storage capacity for the subsetof ∼4000 compounds exhibiting nontrivial internal porosity. Our screening identifies several overlooked compounds having hightheoretical capacities; these compounds are suggested as targets of opportunity for additional experimental characterization.More importantly, screening reveals that the relationship between gravimetric and volumetric H2 density is concave downward,with maximal volumetric performance occurring for surface areas of 3100−4800 m2 /g. We conclude that H2 storage in MOFswill not benefit from further improvements in surface area alone. Rather, discovery efforts should aim to achieve moderate massdensities and surface areas simultaneously, while ensuring framework stability upon solvent removal.