AMES, Iowa -- Researchers at the U.S. Department of Energys Ames Laboratory are employing some modern day alchemy in an effort to find a material with properties of rare and high-priced palladium. If theyre successful, it could remove a major roadblock from the path of hydrogen fuel-cell powered vehicles.
Hydrogen fuel-cell technology sounds almost too good to be true. You combine cheap and plentiful hydrogen and oxygen gas, the fuel cell generates electricity and the by-product is simply water. But its a little more involved.
The key is a proton exchange membrane, or PEM, containing platinum. The platinum acts as a catalyst that separates electrons from the hydrogen gas atoms. The free electrons are gathered as current and the positively charged hydrogen ions pass through the membrane where they readily combine with oxygen atoms to form water. But if the hydrogen gas contains impurities, such as water vapor or carbon monoxide, it can "gum up" the fuel cells separation membrane, dropping efficiency or halting the process altogether. Pure hydrogen, however, is hard to come by, and thats where palladium enters the picture.
"Hydrogen is tough to handle because of the small size of the atoms and because it naturally wants to bond with other elements," said Ames Laboratory scientist Alan Russell, one of the investigators on the project. "Palladium acts like an atomic filter the hydrogen atoms readily diffuse right through the metal."
In the conventional approach to purifying hydrogen, an alloy of 73 percent palladium and 27 percent silver is drawn into long thin tubes, about 3 mm in diameter and 20 feet long. Clusters of these tubes are placed inside a vacuum chamber and heated to between 400 and 500 Celsius. Impure hydrogen gas is then pumped into the small tubes, and the hydrogen readily diffuses through the palladium-silver tube walls and is captured in the outer chamber while the impurities travel out the other end of the t
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