On the Mechanism of Hydrogen Storage in a Metal−Organic Framework Material

Department of Chemistry, University of South Florida, Tampa, Florida, United States
Journal of the American Chemical Society (Impact Factor: 12.11). 01/2008; 129(49):15202-10. DOI: 10.1021/ja0737164
Source: PubMed


Monte Carlo simulations were performed modeling hydrogen sorption in a recently synthesized metal-organic framework material (MOF) that exhibits large molecular hydrogen uptake capacity. The MOF is remarkable because at 78 K and 1.0 atm it sorbs hydrogen at a density near that of liquid hydrogen (at 20 K and 1.0 atm) when considering H2 density in the pores. Unlike most other MOFs that have been investigated for hydrogen storage, it has a highly ionic framework and many relatively small channels. The simulations demonstrate that it is both of these physical characteristics that lead to relatively strong hydrogen interactions in the MOF and ultimately large hydrogen uptake. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction. Previous simulations of hydrogen storage in MOFs and other materials have not focused on the role of polarization effects, but they are demonstrated here to be the dominant contribution to hydrogen physisorption. Indeed, polarization interactions in the MOF lead to two distinct populations of dipolar hydrogen that are identified from the simulations that should be experimentally discernible using, for example, Raman spectroscopy. Since polarization interactions are significantly enhanced by the presence of a charged framework with narrow pores, MOFs are excellent hydrogen storage candidates.

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    • "However, significant hydrogen adsorptive storage capacities in physisorption need to be reached at liquid-nitrogen temperatures (77 K) and pressures of several MPa. This is attributed to weak binding energy between molecular hydrogen and the surface of sorbents in the range of 2–5 kJ mol À 1 H 2 [8] [9] [10] [11] [12]. Generally, the hydrogen storage properties of physisorption appear to be limited by specific surface area (SSA), pore structures and pore size distributions, surface functionality and the bulk density of the adsorbents. "
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