Hydrogen storage in metal-organic and covalent-organic frameworks by spillover

Covalent-organic framework COF-1 and metal-organic frameworks HKUST-1 and MIL-101 were synthesized and studied for hydrogen storage at 77 and 298 K. Although MIL-101 had the largest surface area and pore volume among the three materials, HKUST-1 had the highest uptake (2.28 wt %) at 77 K. However, the H-2 storage capacity at 298 K and high pressure correlated with the surface area and pore volume. The H-2 storage in the COF and MOF materials assisted by hydrogen spillover, measured at 298 K up to a pressure of 10 MPa, have been examined for correlations with their structural and surface features for the first time. By using our simple technique to build carbon bridges, the hydrogen uptakes at 298 K were enhanced significantly by a factor of 2.6-3.2. The net uptake by spillover was correlated to the heat of adsorption through the Langmuir constant. Results on water vapor adsorption at 298 K indicated that COF-1 was unstable in moist air, while HKUST-1 and MIL-101 were stable. The results suggested that MIL-101 could be a promising material for hydrogen storage because of its high heat of adsorption for spiltover hydrogen, large surface area and pore volume, and stability upon H2O adsorption. (C) 2007 American Institute of Chemical Engineers.