Types of fuel cells
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There are several different types of fuel cells, each based on a different chemistry and suited to different situations.
Fuel cells are generally classified by the type of electrolyte they use and their operating temperatures. The main types of fuel cells include:
Alkaline fuel cell (AFC)
One of the oldest fuel cell designs. The AFC is susceptible to contamination and so requires pure hydrogen and oxygen. It generally uses potassium hydroxide in water as the electrolyte. Its efficiency is about 70% and the operating temperature ranges from 150 to 200 degrees Celsius. Fuel cell output ranges from 300 watts to 5 kilowatts.
Direct methanol fuel cell (DMFC)
These fuel cells operate at around 80 degrees Celsius with their efficiency normally below 40%. The DMFC needs a large amount of platinum which acts as the catalyst and so they can be expensive.
Molten carbonate fuel cell (MCFC)
This type of fuel cell is best suited to large power generators. MCFC uses high temperature compounds of salt carbonates as the electrolyte. Efficiency ranges between 60% and 80% and the operating temperature is about 600 degrees Celsius, so the steam that is produced can be used to generate more power. Their output is generally in the range of 2 megawatts up to 100 megawatts.
Phosphoric acid fuel cell (PAFC)
The electrolyte is phosphoric acid. Efficiency ranges from 40% to 80% and the operating temperature is between 150 to 200 degrees Celsius. PAFC have outputs up to 200 kilowatts, although units with 11 megawatts output have been tested. A wide variety of fuels can be used in this system.
Polymer exchange membrane fuel cell (PEM)
This fuel cell works with a polymer electrolyte in the form of a thin, permeable sheet or layer. Efficiency ranges from 40% to 50% and the operating temperature is around 80 degrees Celsius. Fuel cell outputs range from 50 to 250 kilowatts.
Solid oxide fuel cell (SOFC)
Uses a hard, ceramic compound of metal oxides to act at the electrolyte. Efficiency is about 60% and they operate at temperatures of 1000 degrees Celsius. The output from SOFC is up to 100 kilowatts. Waste heat can be recycled in order to produce more electricity.
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