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New Materials for Hydrogen Storage |
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Metal-organic frameworks, extended
crystalline solids composed of metal clusters and bridging organic
ligands, have been shown to adsorb
hydrogen reversibly at cryogenic temperatures, thus showing promise
as potential H2 storage materials for mobile applications. Our group focuses on the synthesis
of novel microporous
metal-organic frameworks that contain unsaturated metal centers for
stronger H2 binding.
We use a combined approach based on new ligand
design and the investigation or functionalization
of known materials, such as Prussian blue analogs or Zn4O(BDC)3
(BDC = 1,4-benzenedicarboxylate). Our approach has led, for example,
to the synthesis of an entire series of tetrazolate ligands,
which form frameworks isostructural
to those formed by the analogous carboxylic acids, but also display
new reactivity through the four nitrogen atoms available for metal
coordination. One such framework, Mn3[(Mn4Cl)3(BTT)8(CH3OH)10]2
(BTT = 1,3,5-benzenetristetrazol-5-yl), displays a robust cubic structure
(shown), within which unsaturated Mn2+ cations strongly bind H2 molecules, leading
to an H2 adsorption enthalpy of 10.1 kJ/mol, and total
gravimetric and volumetric uptakes of 6.9 wt% and 60 g/L at 77 K and
90 bar, among the highest so far for microporous
materials. Typical
techniques used for the discovery of new materials include classic
organic synthesis for new ligands,
and solvothermal
synthesis for the crystallization of extended solids, while characterization
of new materials is typically
achieved through single-crystal and powder X-ray diffraction,
thermogravimetric analysis, and gas adsorption measurements.
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