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Applications for Fullerenes in Hydrogen Storage
Achievement/Results
IGERT Patrick Ward (Chemistry)and Professor Robert Compton (Chemistry) from the University of Tennessee, as well as researchers at Savannah River National Lab (Joseph Teprovich, Ragaiy Zidan (PI), and Douglas Knight) have been investigating materials based on C60¬ fullerene that have the capability of reversibly storing hydrogen. These materials, originally discovered by Zidan et. al., give many examples of how C60 fullerene can play a role as hydrogen storage materials. Further investigation into the exact composition and physisorption properties of the materials was achieved by an interdisciplinary collaboration between the two institutions. By having chemists and physicists working together, a deeper understanding of the materials could be accomplished.
This work was funded by the NSF’s Sustainable Technology through Advanced Interdisciplinary Research (STAIR) IGERT program and by the Department of Energy’s Basic Energy Science. C60¬ can act as a catalyst, therefore lowering the activation energy required for hydrogen evolution, for the complex metal hydride lithium borohydride (LiBH4). Also, the presence of fullerene allowed LiBH4 to regenerate stored hydrogen under much milder conditions than pure LiBH4. This catalytic effect was found to be occurring on the fullerene surface which is unlike other catalysts used for LiBH4. Understanding how catalysis takes place on the surfaces of carbons materials could lead to the development of cheaper and more renewable catalytic systems to replace or reduce the need for rare earth metals. Furthermore, C60 fullerenes can store hydrogen on the fullerene cage by chemisorption. The amount of hydrogen capable of being stored is significantly increased by lithium and sodium doping of the material. By altering the electronic structure of the material with alkali metals, hydrogenation of the fullerene can be accomplished under milder conditions and to a greater extinct.
Recent findings have also shown an increase in the hydrogen physisorption properties of fullerenes with both sodium and lithium doping. Due to the charge transfer between the alkali metal and the fullerene cage, there is an induced dipole moment in the molecular orbital of hydrogen when the molecule approaches the cage. This allows for a stronger interaction between hydrogen and the alkali doped fullerenes in comparison with pure fullerenes. While the crystalline nature of the fullerenes still limits its uptake, this finding shows that porous carbon materials based on alkali doped fullerenes could have potential for cryogenic hydrogen storage.
Address Goals
The research of Patrick Ward is aimed at developing new metal-decorated carbon-based materials that allow for reversible high-capacity hydrogen storage. Such a material, satisfying the DOE requirements for gravimetric and volumetric hydrogen capacity as well as charging/discharging rates, does not currently exist. Such a storage material is targeted for hydrogen fuel cell vehicles, which would operate without generating green house gases and would have the same range as internal combustion vehicles (~300 miles/tank) as opposed to electric battery vehicles like the Nissan Leaf, which have a much more limited range.
