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Sustainable Energy

Cheaper Fuel Cells

A new membrane makes fuel cells more powerful and less expensive to produce.

Fuel cells still cost too much to be a viable alternative for internal combustion engines in cars – they require expensive materials and are difficult to make. Now, according to results presented last week at the American Chemical Society meeting in Atlanta, a new, simple-to-produce material boosts the performance of fuel cells many times – and could be a major step toward making them affordable.

The University of North Carolina at Chapel Hill researchers who developed the new material say it can “dramatically outperform” the material now used to form fuel-cell membranes. Proton-exchange membranes are used in fuel cells to sort protons and electrons, by allowing the protons to pass through them from one electrode to the other, while blocking electrons and forcing them to travel between electrodes via an external circuit, powering a motor or other electronic device along the way.

[To see images of the new material for fuel cells, click here.]

The researchers say the new membrane conducts protons nearly three times as well as the currently used material, significantly improving power density. Also, unlike the current material, the new membrane can be easily molded into patterns to increase its surface area. By increasing the area by up to 60 percent, the researchers have further doubled the power density of a fuel cell. Joseph DeSimone, the UNC-Chapel Hill chemistry and chemical engineering professor who heads the lab where the work was done, thinks they can increase the membrane’s surface area 20 to 40 times by using different patterns, increasing the power density proportionately.

Such improvements in power density mean that a much smaller fuel cell could provide adequate power for a vehicle. The material is also easier to work with, which should reduce manufacturing costs. It begins as a liquid that can be poured over a patterned mold, something that’s not possible with the material now primarily used in membranes, a fluorinated polymer called Nafion made by DuPont, which is solid at room temperature. Once in a mold, the liquid form of the new material is cured with light to form a resilient solid. “Fuel-cell cars are currently ten times as expensive as conventional cars,” says James McGrath, chemistry professor at Virginia Tech. “A lot of that is related to processing. If you can simplify the processing, that would be great. Joe [DeSimone]’s liquid processing technique has a lot of potential for fabricating the intricate patterns necessary to produce a fuel cell.”

DeSimone says that a clearer idea of potential cost savings from their new material should be available within six months. And he expects that fuel cells using the membrane could be in production within two to three years.

The new material is a long-needed advance, says Brian Benicewicz, professor of chemistry at Rensselaer Polytechnic Institute (RPI). “For about 30 years now, everybody has used the exact same piece of Nafion, or the same Nafion-like product. We have 30 years of history that shows what the problems are, and a number of engineering solutions to get around the problems with the membrane. What is refreshing about Joe’s approach is that now, instead of engineering around a problem membrane, he’s actually going back and trying to engineer a better membrane.”

The enhanced conductivity of the new material comes in part from having a higher acid content than Nafion – by definition, acids tend to give up protons, allowing protons to move freely through the material. The amount of acid that can be incorporated into Nafion is limited – too much acid and its polymers dissolve in water. Because the new material forms a cross-linked polymer once cured, it doesn’t dissolve in water, even after being heavily loaded with acid. As a result, “the conductivity goes through the roof,” says DeSimone.

While the material has been tested using hydrogen as a fuel, DeSimone says the lab is now testing the material with methanol – a fuel source that could be important for fuel cells in portable electronics, and maybe vehicles.

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