High Capacity Step-Shaped Hydrogen Adsorption in Robust, Pore-Gating Zeolitic Imidazolate Frameworks

Recipient Colorado School of Mines/CSM (PI: Mike McGuirk)

Abstract Despite motivation from government and industry to dramatically increase the use of molecular hydrogen as an alternative fuel in the transportation sector, intertwined technological and economic limitations have stunted progress. While significant effort from the scientific community has been applied to the beginning (i.e., production) and end (i.e., use) stages of the hydrogen life cycle, inefficiencies in the intermediary stages (i.e., transportation and delivery) have been comparatively under addressed, preventing broader acceptance of this alternative fuel source. The current state-of-the-art for hydrogen transportation and storage requires overwhelming energetic input in the forms of compression (200¬–500 bar) or cryogenic liquefaction (BP = 20 K) to achieve requisite volumetric energy densities. Producing and maintaining such extreme conditions invariably yields significant energetic inefficiencies, dramatically increasing the net cost of hydrogen use. Therefore, the purview of the proposed work is the development, characterization, and validation of designer porous materials that promote the energetically efficient storage and delivery of high volumetric capacities of hydrogen under considerably milder conditions during transport. Specifically, we propose a family of robust porous materials capable of adsorbing and, most importantly, desorbing large quantities of hydrogen gas at elevated pressures relevant to fueling in an unprecedentedly efficient, on-demand manner. This will be achieved with a class of structurally responsive “pore-gating” zeolitic imidazolate frameworks (ZIFs), recently discovered by the project lead, that physically adsorb and desorb molecular gases in an energetically efficient, non-classic “step-shaped” fashion.2 Our efforts under this proposal will seek to chemically optimize these ZIF materials for use in hydrogen storage under technologically relevant conditions, therefore achieving transformative efficiencies in hydrogen on- and off-loading during transportation.