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Dual design for "coal-fired" fuel cells.

Burning coal to fuel power plants represents a relatively inefficient way of transforming the energy tied up in carbon's chemical bonds into electricity. In addition, attempts during the last century to make carbon-based fuel cells first required converting the element to carbon monoxide, which also reduced the efficiency of energy production, says Turgut M. Gur, an electrochemist at Stanford University.

Now, Gur and Robert A. Huggins from the Center for Solar Energy and Hydrogen Research in Ulm, Germany, report in the October JOURNAL OF THE ELECTROCHEMICAL SOCIETY that a two-compartment, high-temperature fuel cell can use raw carbon.

"It's just a preliminary experiment," Gur says, "but it demonstrates that one can, without pretreatment, convert the chemical energy of coal [directly] into electrical energy. This has not been shown before."

In the fuel cell, one compartment houses a yttria-zirconia tube, which transports oxygen to the carbon. The other holds carbon pellets. The dual-chamber design lets the researchers regulate the temperature of the carbon and of the zirconia independently. Thus, they can heat the zirconia electrode to 800[degrees]C yet leave the carbon cool enough--below 700[degrees]C -- that it combines with oxygen to form carbon dioxide rather than carbon monoxide. That reaction doubles the energy yield per carbon atom, say Gur and Huggins. However, the carbon and oxygen tend to react much more slowly at this lower temperature. Consequently, the prototype fuel cell does not generate sufficient current or power to be of practical use, they add.

By using a fluidized bed of fine coal bits, they expect to increase the surface area of carbon exposed to oxygen and speed up the reaction rate. In this way, their approach could eventually lead to technologically useful energy yields, says Gur. Also, this fuel cell would, in theory, turn sulfur and other impurities in coal into energy, he notes.
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Title Annotation:research proves chemical energy of coal can be converted into electrical energy
Publication:Science News
Article Type:Brief Article
Date:Nov 7, 1992
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