a Posted on 05/05/2005 8:08:06 PM PDT by ckilmer
'Metal-Decorated' Nanotubes Hold Promise for Fuel Cells
May 04, 2005
New quantum calculations and computer models show that carbon nanotubes "decorated" with titanium or other transition metals can latch on to hydrogen molecules in numbers more than adequate for efficient hydrogen storage, a capability key to long-term efforts to develop fuel cells, an affordable non-polluting alternative to gasoline.
a
Image: This computer model shows how titanium atoms (dark blue) can attach above the centers of single-walled carbon nanotubes (light blue). Quantum calculations and modeling by a NIST researcher and his colleague reveal that each titanium atom can bond with four hydrogen molecules (red), a finding that could lead to efficient fuel cells for future automobiles. Image Credit: T. Yildirim/NIST
National Institute of Standards and Technology theorist Taner Yildirim and physicist Salim Ciraci of Turkey's Bilkent University report their "unanticipated" findings in the online issue of Physical Review Letters.*
Using established quantum physics theory, they predict that hydrogen can amass in amounts equivalent to 8 percent of the weight of "titanium-decorated" singled walled carbon nanotubes. That's one-third better than the 6 percent minimum storage-capacity requirement set by the FreedomCar Research Partnership involving the Department of Energy and the nation's "Big 3" automakers.
As important, the four hydrogen molecules (two atoms each) that link to a titanium atom are relinquished readily when heated. Such reversible desorption is another requirement for practical hydrogen storage.
Resembling exceedingly small cylinders of chicken wire, so-called single-walled carbon nanotubes are among several candidate materials eyed for hydrogen storage. Reaching the 6 percent target, however, has proved difficult—a potential "showstopper," according to many in the field. Positioning a titanium atom above the center of hexagonally arranged carbon atoms (the repeating geometric pattern characteristic of carbon nanotubes) appears to resolve the impasse according to this new study.
The new results, obtained with a method for calculating the electronic structure of materials, surprised the researchers. Interactions among carbon, titanium and hydrogen seem to give rise to unusual attractive forces. The upshot is that four hydrogen molecules can dock on a titanium atom, apparently by means of a unique chemical bond of modest strength. Several forces at work within the geometric arrangement appear to play a role in the reversible tethering of hydrogen, Yildirim says.
Yildirim and Ciraci report that their findings "suggest a possible method of engineering new nanostructures for high-capacity storage and catalyst materials." The work was funded, in part, by the Department of Energy and National Science Foundation.
*T. Yildirim and S. Ciraci, "Titanium-Decorated Carbon Nanotubes as a Potential High-Capacity Hydrogen Storage Medium", Phys. Rev. Lett. 94, p. 175501 (2005).
Source: NIST
Did they do an MD simulation on this, and how do you position the titanium atoms just so?
Carbon-based structures such as nanotubes and fullerenes (spherical cage-like structures, like C60 "buckyballs") have good adsorption (yes, that is a 'd') properties. Strongest attractors at low temperature.
Might have been molecular dynamics. Depends on the working temperature. If it is below 100 K, I don't think MD would give good results, since zero point motion is neglected. You would need to use a quantum approach (like Path Integral Monte Carlo). Haven't read their PRL yet, so I don't know. I also wonder how titanium effects the desorption temperature.
don't know. beats me.
judging by the general references to computer simulation though and the complexity of the project -- its not likely they came up with this on the chalkboard.
all they have done as far as I can tell is stumble on a molecular design that's possible--ie it doesn't violate any rules of physics-- using a mathematical formula that's alluded to but not explained in detail.
there's no reference to how the molecule would be built either singly or in quantity.
whoa nelly ... carbon nanotubes on a per-pound basis are very expensive ... so you can go that route, or you can have a gas tank that is stamped plastic and/or metal.
Dont expect this to be practical enough.
In a similar concept, they expect to make all-new compounds very soon using "caged" molecules, where particular atoms or small molecules are trapped within buckyballs or nanotubes.
actually nanotechnology is the next big thing. But its expected to be much bigger than say, computers as it gets into the entire industrial base....at least before third generation computing--which includes stuff like rfid and smart dust
they have ways to scale up production of this nanotech. I couldn't tell you the details however. I Just know it a 4-5 billion dollar biz this year. I've read they expect it to scale up a hundred fold in ten years.
It's not an alternative to gasoline as an energy source, only an alternative as a delivery method. That energy still has to be put into the hydrogen cell, being manufactured either by burning oil or coal, or by nuke power, which has its own special kind of pollution. We still have to get the energy from somewhere - hydrogen fuel cells won't charge themselves.
What this will do with regards to pollution will allow it to be directed somewhere else, rather than at the point of consumption. In other words, all that bad city air is moving to the wide open spaces where there are fewer people to complain about it.
" I don't think MD would give good results, since zero point motion is neglected."
Ahhh yes but I find the flux capacitor much more effecient than the traditional zero point module...
:-) Just poking a little fun :)
Interesting stuff!
Not with a closed cycle and reversible fuel cell coupled to solar cells.
Well the nanotubes themselves are already in commercial products. Golf club heads , among others. I doubt getting the titanium atoms to attach at the right places wouldn't seem all that difficult, because where else would they go. those probably being the natural attachment points in the carbon nanotube structure.
Heck, I was doing that 10 years ago. Never went anywhere, but I got an undergraduate senior thesis out of it.
The catch is always about scaling it up, both technically and economically. The most powerful explosive known right now can only be made in microscale amounts.
Yes! Nanotubes and fuel cells, some of my favorite phrases!
Why not electrolysis from water molecules into hydrogens by OTEC or OWEC? :)
One company built and experimental filling station (in CA I believe) that used solar cells to electrolyze water into H2. They could pull off the grid if there wasn't enough sunlight (cloudy/rainy days) but it was designed to operate primarily by solar power.
I'm anxious to see what will happen when InGaN solar cells come online, as that will dramatically increase their efficiency and might make them more practical for this purpose.
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