July 2, 2012

Zombie Fuel Cells

Brett Smith for - Your Universe Online

We´ve heard about batteries that keep going and going, but scientists have taken the next step and created an energy source that keeps going even after its fuel is gone.

This ℠zombie´ fuel cell, which is a fraction of the size of a standard AA battery, converts hydrogen to electricity, but also has the ability to store electrical chemical energy. The stored energy can then be tapped into after the cell´s hydrogen fuel supply is exhausted.

Harvard researchers detailed the development of the solid-oxide fuel cell (SOFC) in a recent report published online in Nano Letters.

"This thin-film SOFC takes advantage of recent advances in low-temperature operation to incorporate a new and more versatile material," explains the study´s co- author Shriram Ramanathan, Associate Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS). "Vanadium oxide (VOx) at the anode behaves as a multifunctional material, allowing the fuel cell to both generate and store energy."

The new SOFC uses a bilayer of platinum and VOx for the anode, which allows the cell to continue operating without fuel for up to 3 minutes and 30 seconds. While this newest fuel cell lasted 14 times longer than their previous model, Ramanathan and his team predict that future improvements to the composition of the VOx-platinum anode will further extend the cell's lifespan.

As the fuel cell is converting hydrogen to electricity, it is theoretically able to store electrical energy by three different reaction mechanisms.

"There are three reactions that potentially take place within the cell due to this vanadium oxide anode," says Ramanathan. "The first is the oxidation of vanadium ions, which we verified through XPS (X-ray photoelectron spectroscopy). The second is the storage of hydrogen within the VOx crystal lattice, which is gradually released and oxidized at the anode. And the third phenomenon we might see is that the concentration of oxygen ions differs from the anode to the cathode, so we may also have oxygen anions being oxidized, as in a concentration cell."

The Harvard researchers have so far determined that at least two of three possible mechanisms are simultaneously at work, but it is currently unclear exactly what allows the new fuel cell to keep running.

This mysterious development will be most likely be important for small-scale, portable energy applications, where a very compact and lightweight power supply is needed and the chances the fuel supply may be interrupted need to be minimized. The research, which was funded in part by the Department of Defense, will most likely be used in military as well as civilian applications.

"Unmanned aerial vehicles, for instance, would really benefit from this," said lead author Quentin Van Overmeere, a postdoctoral fellow at SEAS. "When it's impossible to refuel in the field, an extra boost of stored energy could extend the device's lifespan significantly."

Ramanathan and his colleagues said that a more advanced fuel cell of this type, able of producing power without fuel for a longer period of time, will be available for testing in mechanical devices within 2 years.

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