How Fuel Cells Work
THE MAGAGINE DEVOTED TO NICKEL AND ITS APPLICATIONS
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250-kW FUEL CELL UNIT at Yale University in Connecticut, U.S.A.
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Nickel strip and power metallurgy play a key role in fixed-station fuel cell technology. By
John Milne
Nickel magazine, October, 2003 -- A fuel cell is a device that chemically combines
hydrogen and oxygen to activate the generation of electricity. The only significant byproducts are heat and
water vapour, making this an environmentally ideal means of generating electricity.
There are various types of fuel cells. Some use hydrogen that has been generated externally as a fuel. Others use a hydrocarbon fuel which is dissociated, or reformed, into hydrogen inside the unit. Following, is a description of one such fixed-station fuel cell which is manufactured by FuelCell Energy Inc.
These fuel cells consist of a sandwich of an anode, made of porous nickel strip and a cathode made of nickel oxide strip, separated by a ceramic-based matrix layer. A carbonate electrolyte, soaked into the matrix layer, facilitates the electro-chemical reaction between the anode and the cathode.
The nickel strip used for both the anode and cathode is made using a powder metallurgy technique. A slurry of micron-size nickel powder is evenly distributed on a moving belt that then passes through a sintering furnace and through rolls that compact and increase the density of the powder strip. This process is called tape casting.
Nickel is the ideal material for this as it is a good conductor of heat and is resistant to corrosion. It is not consumed in the process.
A hydrocarbon, such as natural gas, enters the fuel cell and is chemically dissociated, or reformed, by the catalyst so that hydrogen feeds the anode and air (oxygen) enters the cathode. The reaction splits the fuel into ions and electrons. The electrons move from the anode by means of a conventional copper bus bar external circuit while the ions move through the electrolyte to produce carbon dioxide and water by-products. The heat generated (in the 370°C range) can be captured and used.
A single fuel cell generates only a small amount of electricity and measures 1.2 meters by 0.7 meter by 0.63 centimetres thick. However, by stacking 350 to 400 fuel cells in a module, that module will produce 250 kW of electricity. Multiple modules can be packaged into larger units for one to 2 megawatts of power.
Efficiency of electricity generated by this type of fuel cell is about 50%, and can be as high as 80% with co-generation use of the byproduct heat. As development of fuel cells continue to reduce costs and improve efficiency, they offer a competitive alternative to conventionally generated electric power, with the advantage of being non-polluting and quiet for on-site use.
FuelCell Energy and its partners operate field trial fuel cell power units in Japan, Germany and the
U.S.A., such as the 250-kW unit pictured here at Yale University's Environmental Sciences Building.
John Milne is a consultant to the Nickel Development Institute.
PHOTO/DIAGRAM: FuelCell Energy Inc.
 FuelCell Energy Inc. |
