02 October 2002
Fuel cells face reform
We all know fuel cells are the future power plant for automobiles. But engineers are still scratching their heads over how to economically supply the hydrogen gas needed to power a fuel cell.
Chemical engineers at Argonne have now developed and patented a compact fuel processor that "reforms" ordinary gasoline into a hydrogen-rich gas to power fuel cells.
Fuel cells convert hydrogen gas into electricity and water. Compared with internal combustion engines, the energy conversion is clean and efficient. "You can think of fuel cells as batteries that are continuously charged by supplying fuel," said Jim Miller, manager of Argonne's Electrochemical Technology Program.
A team of scientists in the Chemical Technology division synthesized new types of catalysts to form hydrogen by reacting gasoline with oxygen. Catalysts are materials that speed chemical reactions by cutting the energy required to start the reaction. While catalysts help some chemical bonds form and others break, catalysts remain unchanged. Using the Argonne catalyst, scientist Shabbir Ahmed designed and built an inexpensive, easy to manufacture, fuel-reforming reactor.
Fuel cell engines efficiently convert hydrogen and oxygen into electric power with water and heat as the only by-products. The efficiency of a fuel cell should be about 60%-twice as efficient as today's internal combustion engines. At the same time, fuel cells should cut carbon dioxide output to half that of a combustion engine.
Using hydrogen directly to power fuel cell engines would be environmentally ideal, but it is not practical today. Hydrogen storage devices are heavy and bulky, and no retailing infrastructure exists for supplying hydrogen to consumers. These challenges prompted scientists to investigate compact processors that could produce hydrogen from conventional fuels to power the fuel cell onboard the vehicle.
Researchers originally developed methanol reformers but switched to gasoline because of the existing production, distribution, and retailing infrastructure. Fuel cell car owners would use the pumps at the gas station to refuel just as they do now, but they would need only half as much gas.
In designing the fuel reformer, Ahmed used a simple, inexpensive plan similar to catalytic converters in today's cars. Catalytic converters pass the car's exhaust over a catalyst that converts carbon monoxide to carbon dioxide to eliminate the poisonous gas.
In Ahmed's gasoline reformer, vaporized gasoline mixes with steam and air and then goes through a catalyst-packed cylinder. The result is a mixture of gases with a high hydrogen concentration, which feeds to the fuel cell. Some carbon monoxide is also present in the gas mixture. Before it goes to the fuel cell, it passes through a secondary processor, where water vapor and the carbon monoxide react to form carbon dioxide and additional hydrogen.
In addition to the reformer design, researchers needed new catalysts to spur the gasoline-to-hydrogen-gas chemical reaction. Hydrogen gas consists of twin hydrogen atoms bound together. The scientists needed something that could pull hydrogen atoms from the fuel molecules and combine them into the diatomic gas.
Before they found catalysts that worked well with gasoline, scientist Mike Krumpelt and Ahmed tried several different kinds of catalysts with no success.
They realized the anode (the negative electrode) could be a model for their fuel-reforming catalyst. "If these types of materials worked in a fuel cell environment," Krumpelt said, "then they should work as catalysts in the kind of reformer system we were seeking."
Argonne scientists combined this idea with information from Argonne's fuel cell research. Krumpelt and Ahmed used metal and oxygen compounds similar to those used in fuel cell research as a substrate and coated it with platinum compounds. When the gasoline/air mix contacts the catalyst, the end result is hydrogen.
The researchers theorized that the supporting substrate material helps oxidize the carbon, forming carbon dioxide, and the platinum pulls the hydrogen atoms off the substrate to form the gas.
Scientists are now working to understand how the catalysts and reformer work and to make improvements. For example, they are experimenting with metals cheaper than platinum for the catalyst to lower the cost of the reformer. They are testing the "engineering-scale" reformer and designing a full-scale version.
Argonne's reforming catalyst has been licensed to Süd-Chemie, formerly United Catalysts Inc.
Argonne researchers also have a cooperative research and development agreement with H2fuel, which is a joint venture between Unitel Technologies in Mount Prospect, Ill., and Avista Labs in Spokane, Wash.
H2fuel built and tested a fuel processor. Through a series of catalytic reactions, this first-generation unit converted gasoline, natural gas, or ethanol into a gas containing about 45% hydrogen. During the next two years, H2fuel and Argonne's Chemical Technology division will work to improve this processor to the point where it is ready to enter the marketplace.
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