Lithium buckyballs to store hydrogen?
Hydrogen fuel, which is an ideal energy carrier and environmentally friendly because it releases only water in the air, might one day power our cars and reduce our dependency on fossil fuels. But first we need to find ways to produce it -- and to store it. And now, researchers at Virginia Commonwealth University (VCU) have developed a new storage system for hydrogen based on lithium-coated buckyballs. The clusters they've designed -- by using computer modeling -- are composed of 12 lithium atoms and 60 carbon atoms, are very stable and can store up to 120 hydrogen atoms in molecular form. The researchers now have to prove that hydrogen can be stored in the lithium-coated fullerenes. Read more...
The VCU news release starts by a general introduction about why we need to develop alternatives to fossil fuels before giving some details about this new way of storing hydrogen, developed by Puru Jena, a professor of physics at VCU.
In [a recent technical paper,] Jena and his team describe the theoretical composition of a material -- a lithium-coated buckyball -- that may have the potential to serve as a storage vessel for hydrogen atoms. A buckyball is a soccer ball-shaped nanoparticle containing 60 carbon atoms. Essentially, the lithium buckyballs absorb the hydrogen.
Now, let's look at some graphical representations of this theoretical work. Below are two images showing the initial (left) and optimized (right) geometries of these lithium-coated clusters (Credit: VCU). Lithium, carbon and hydrogen atoms are represented respectively in purple, grey and white).
On this second series of images, you can see the initial geometry (a) and the fully optimized geometry (b) for H2 on dimer -- a polymer containing two monomers (Credit: VCU).
This research work has been published online on July 6, 2006 by the Journal of the American Chemical Society under the title "First-Principles Study of Hydrogen Storage on Li12C60" (Volume 128, Number 30, Pages 9741 -9745, August 2, 2006). Here is a link to the abstract.
The full paper is not freely available online, but Sathya Achia-Abraham, from VCU, sent me a copy of it. The illustrations on this post have been extracted from this paper.
But why did the researchers choose to study this particular kind of material to store hydrogen?
There are two classes of materials: one where large amounts of hydrogen can be stored, but it is difficult for hydrogen to desorb (e.g., CH4), and the other where hydrogen can desorb easily, but not much of it can be stored (e.g., carbon nanotubes). An ideal storage system would be one where hydrogen binds molecularly but with a binding energy that is intermediate between the physisorbed and chemisorbed state. We show that coating of C60 fullerenes with suitable metal atoms may lead to the synthesis of novel hydrogen storage materials. In particular, we show that the unusual ability of Li12C60 to bind 60 hydrogen molecules stems from the unique chemistry at the nanoscale.
And here are some conclusions from the researchers.
We have shown that Li12C60 is a promising system to store hydrogen in molecular form with high gravimetric and volumetric densities. Equally important is the fact that this system can also store more hydrogen per weight and volume than many of the light metal hydrides.
We believe that the predicted results are interesting enough that attempts should be made in the laboratory to study the hydrogen storing capacity of an isolated Li12C60 cluster and to assemble these clusters to synthesize bulk materials. We also hope that these results may lead researchers to a new line of thinking and to the eventual design and synthesis of ideal storage materials.
So will we see one day lithium-based tanks in future hydrogen refueling stations? It's too early to be sure.
But thanks again to Sathya for sending me a copy of the VCU research paper.
Sources: Sathya Achia-Abraham, Virginia Commonwealth University News Services, July 24, 2006; and various web sites
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