(483c) Large-Scale Topologically-Guided Design of Metal-Organic Frameworks and Application to Cryo-Adsorbed Hydrogen Storage

Metal-organic frameworks (MOFs) are porous crystalline materials constructed by combining molecular inorganic and organic building blocks into different topological nets.  The combinatorial possibilities give access to an almost unlimited diversity of pore structures with different chemical and textural properties that can in principle be exploited in a wide variety of  applications such as catalysis, separations, and gas storage. Major challenges are to efficiently identify what combinations of building blocks and topologies constitute MOFs that are both outstanding and synthesizable and to discern the performance boundaries of these materials.  Here, we demonstrate an automated, topologically-guided approach to computationally construct MOFs and use it to generate a population of 13,512 MOFs encompassing 41 distinct topologies. 

All structures were evaluated using grand canonical Monte Carlo simulations to determine the viability of using the MOFs for cryo-adsorbed hydrogen storage at 100 bar.  We find a topological dependence of hydrogen storage performance, which is linked to the topological dependence of property-property relationships of the investigated MOFs. A large number of structures were found to have higher deliverable capacities than the incumbent hydrogen storage technology – which corresponds to a compressed hydrogen gas (CHG) tank at 700 bar and room temperature – and than cryo-compressed hydrogen gas at 100 bar and 77 K.  The heats of adsorptions for the optimal structures were below 5 kJ/mol, which is beneficial for the thermal management of a potential cryo-adsorbed storage system.

Among the topologies that yielded structures for which we predicted cryo-adsorption loadings higher than the CHG tank, we focused on a rare (6,4)-connected MOF topology which had only been accessed synthetically using a “missing linker” strategy to generate 6-coordinated planar inorganic units [1].  Our automated generation approach produced MOFs of this topology based on organic 6-coordinated planar units instead.  We selected some structures of this topology for more detailed study.  We found that this topology is inherently non-catenating and that increasing the storage pressure beyond 100 bar (at 77 K) starts to negate the benefits of placing an adsorbent material in the tank.  Two of the investigated structures were synthesized and activated successfully by our experimental collaborators.

[1] D. Feng, W.-C. Chung, Z. Wei, Z.Y. Gu, Y.P. Chen, D.J. Darensbourg, and H.-C. Zhou, J. Am. Chem. Soc., 2013, 135 (45), pp 17105–17110