Platinum and palladium are two of the most expensive metals on the planet. Platinum is currently running about 30% more expensive than gold. Palladium is about half the cost of gold, but it's still way up there.
These metals are in high demand primarily because they are quite useful as catalysts: they make chemical reactions run more easily, without being used up in the reactions themselves. For example, the catlytic converter in your car probably has about $1000 worth of platinum and palladium in it right now. And those fuel cells that turn hydrogen or methane directly into electricty? They cost tens of thousands of dollars because they use platinum as a catalyst.
So when chemists discover a new class of substances (called "superatoms") that act exactly like platinum or palladium chemically, but that cost hundreds or thousands of times less -- that's big news.
About a decade or so ago, chemists discovered that certain clusters of atoms can behave like a single, very large atom. These clusters are called "superatoms". It was originally theorized that superatoms might extend the periodic table into a third dimension, exhibiting the properties of completely new elements.
It has now been shown that some superatom clusters can not only behave like a single atom, but in fact behave like a single atom of another existing element. Specifically, scientists at Penn State University have found that a supercluster of titanium and oxygen has an electronic signature in its outer electron shells that mimics that of nickel almost perfectly.
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The team used photoelectron imaging spectroscopy to examine similarities between a nickel atom and a titanium-monoxide molecule. Left: Graphical displays of energy peaks were similar between a nickel atom and a titanium-monoxide molecule. Right: Bright spots in the images, which correspond to the energy of the electrons emitted during their removal from the atoms' outer shells, appeared to be similar between a nickel atom (right, top) and a titanium-monoxide molecule (right, bottom). Credit: Castleman lab, Penn State University |
Since nickel is one of the "noble metals", the Penn State chemists decided to move one row down the periodic table and found that the rare and valuable metal palladium could also be replicated by a superatom cluster of zirconium monoxide. Since zirconium is about 500 times less expensive than palladium, this represents a potentially huge reduction in cost for catalysts that use palladium.
Finally, using similar analysis, the Penn State team also found that platinum, the most expensive common metal, can be replicated by a superatom of tungsten carbide. Yes, that's the same tungsten carbide that is used as a superhard coating on expensive drill bits. And it's about 1800 times less expensive than platinum.
Of course, tungsten carbide is usually seen as a crystal, but it has been known for a long time that even in its crystalline form it mimics many of the catalytic properties of platinum. (Now we know why). Caveat: Nobody has actually tested tungsten carbide superatoms for their catalytic ability yet, although given what we already know, we have every reason to be confident in its ability to perform.
Implications for automotive technology
If adopted by the auto industry, your next car could be a thousand bucks cheaper if the catalytic converter uses superatoms instead of noble metals. Yippee!
Implications for fuel cell technology
Think of every place it would be great to use a battery, but you can't because a battery won't last long enough or produce enough power. (Like a car, for example.) Now imagine a battery that produces power to spare, and that you can refill at a filling station. That's a fuel cell.
There are several types of fuel cells, but they fall into two broad classes: Solid Oxide Fuel Cells (SOFCs) run at very high temperatures (1000°C or so), and can use pretty much anything as a fuel. And then there's the kind that run at room temperature and use hydrogen as a fuel. The room-temperature variety are very, very expensive because they use platinum electrodes to catalyze the ionization of hydrogen and oxygen.
Now imagine a fuel cell that runs at room temperature, but costs hundreds of dollars instead of tens of thousands of dollars -- because it's using tungsten carbide superatoms instead of platinum as a catalyst. That's the kind of cost breakthrough we need.
Links:
http://www.eurekalert.org/...
http://www.science.psu.edu/...
Abstract:
http://www.pnas.org/...
Full paper in Proceedings of the National Academy of Science:
http://www.pnas.org/...
Supporting data:
http://www.pnas.org/...