(199e) Computational Screening of Metal-Catecholate Functionalized Metal-Organic Frameworks for Room Temperature Hydrogen Storage

Hydrogen is a promising alternative to fossil fuels as it is non-toxic and carbon-free. However, due to its extremely low volumetric density, the storage and transport of hydrogen for practical applications remain a significant challenge, and high pressure and/or cryogenic temperature is required. Adsorption-based storage utilizing nanoporous adsorbents such as metal-organic frameworks (MOFs) can greatly reduce the storage pressure, but cryogenic or sub-ambient temperatures are required with current adsorbents, which limits the scope of applications. In this work, we aim to search for hydrogen-storage adsorbents that allow room temperature operation by looking at MOFs functionalized with metal catecholate groups, which have highly unsaturated open metal sites and thus greatly enhanced binding strength for hydrogen. We screened a dataset of 2736 zirconium-based MOFs that was constructed in a combinatorial fashion with wide varieties of topologies and linkers. By counting the possible sites that can be functionalized with metal catecholate groups, we were able to obtain the theoretical maximum hydrogen uptake in gravimetric and volumetric units for all of the MOFs. For the 100 MOFs with the highest theoretical uptakes, we built the functionalized structures on the computer and conducted grand canonical Monte Carlo (GCMC) simulations to predict the hydrogen uptake at adsorption (296 K, 100 bar) and desorption (296 K, 5 bar) conditions. The deliverable capacities were calculated by taking the difference of uptakes at those conditions, and we observed >5 wt% and >20 g/L deliverable capacities for some MOFs, which are very high for room temperature pressure swing adsorption cycles. Structure-activity relationships between the structural properties of MOFs and their hydrogen uptakes were also established.