Despite the large hydrogen storage capacities attainable in many porous frameworks at cryogenic temperatures, realizing high ambient temperature capacities remains a challenge given the small enthalpy magnitudes typical of H2 physiosorption. Coordinatively unsaturated metal sites, often accessible within zeolites and metal–organic frameworks (MOFs), can adsorb H2 more strongly, although achieving the ca. –20 kJ/mol that is optimal for ambient temperature storage remains a challenging synthetic task. In this talk, we demonstrate that MOFs containing unsaturated Cu(I) centers within appropriate coordination environments can lead to significantly enhanced H2 adsorption strengths. The important role of π-backbonding renders these Cu(I) sites as effective Kubas-type complexes embedded within a porous framework. These relatively covalent interactions result in adsorption being activated, a result of reversible structural transformations that occur upon H2 dosing as followed by in situ powder neutron diffraction experiments. In addition, variable temperature in situ DRIFTS studies reveal that the thermodynamics associated with H2 sorption are strongly temperature dependent. This trend is investigated through heat capacity measurements and computational investigations, and leads to important ramifications for evaluating the potential of adsorbents towards ambient temperature storage applications.

Leveraging π-basicity in metal–organic frameworks for ambient temperature hydrogen storage: Structural, thermodynamic and kinetic insights

2019 Fall National Meeting

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