High-Throughput Screening of Metal-Organic Frameworks for Hydrogen Storage at Cryogenic Temperature

Metal-organic frameworks (MOFs) have attracted significant interest as a class of adsorbent materials for gas storage applications, including hydrogen storage for fuel cell vehicles. Here, we evaluated 137 953 hypothetical MOFs for hydrogen storage at cryogenic conditions (77 K) by determining the deliverable storage capacity between 100 and 2 bar, using grand canonical Monte Carlo simulations. The highest predicted volumetric capacity for a structure in this study is 50 g/L, and the highest gravimetric capacity is almost 25 wt %. We find that the optimal void fraction is 0.9 and the optimal pore diameter is 12-15 angstrom. MOFs with larger pores have significant regions in the center of the pore with low hydrogen density, which 0 lowers the storage efficiency. We give examples of MOFs with very large pores in which the hydrogen capacity can potentially be increased using catenation or functional groups to reduce the pore size and increase the surface area per volume. We also introduce a screening parameter, the binding fraction, which is the fraction of the unit cell volume within a given distance of the framework. This metric is inexpensive to compute and is a strong predictor of hydrogen storage capacity. This simple parameter could be used to quickly screen even larger numbers of MOFs for gas adsorption capacity to identify the most promising candidates for more detailed study.