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Types of fuel cells

Fuel cells are classified primarily by the kind of electrolyte they use. This determines the kind of chemical reactions that take place in the cell, the kind of catalysts required to enable the reaction, the temperature range in which the cell operates, and the fuel required. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells, each with its own advantages, limitations, and potential applications, as summarized in the following table:

Fuel Cell
Type 		Common Electrolyte Operating
Temperature 		System
Output 		Electrical
Efficiency 		Combined
Heat and
Power
(CHP)
Efficiency 		Applications Advantages
Polymer Electrolyte Membrane (PEM)* Solid organic polymer polyperfluorosulfonic acid 50 - 100°C
122 - 212°F		 <1kW –
250KW 		53-58% (transportation)

25-35% (stationary)		 70-90% (low
– grade
waster heat)
  • Backup power
  • Portable power
  • Small distributed generation
  • Transportation
  • Specialty vehicles
  • Solid electrolyte reduces corrosion & electrolyte management problems
  • Low temperature
  • Quick start-up
Alkaline (AFC) Aqueous solution of potassium hydroxide soaked in a matrix 90 - 100°C
194 - 212°F		 10kW – 100kW 60% >80% (low-grade waster heat)
  • Military
  • Space
  • Cathode reaction faster in alkaline electrolyte, leads to higher performance
  • Can use a variety of catalysts
Phosphoric Acid (PAFC) Liquid phosphoric acid soaked in a matrix 150 - 200°C
302 - 392°F		 50kW – 1Mw (250kW module typical) >40% >85%
  • Distributed generation
  • Higher overall efficiency with CHP
  • Increased tolerance to impurities in hydrogen
Molten Carbonate (MCFC) Liquid solution of lithium, sodium, and/or potassium carbonates, soaked in a matrix 600 - 700°C
1112 - 1292°F		 1kW – 1Mw (250kW module typical) 45-47% >80%
  • Electric utility
  • Large distributed generation
  • High efficiency
  • Fuel flexibility
  • Can use a variety of catalysts
  • Suitable for CHP
Solid Oxide Yttria stabilized zirconia 600 - 1000°C
1202 - 1832°F		 <1kW – 3MW 35-43% <90%
  • Auxiliary power
  • Electric utility
  • Large distributed generation
  • High efficiency
  • Fuel flexibility
  • Can use a variety of catalysts
  • Solid electrolyte reduces electrolyte management problems
  • Suitable for CHP
  • Hybrid/GT cycle

*Direct Methanol Fuel Cells (DMFC) are a subset of PEM typically used for small portable power applications with a size range of about a subwatt to 100w and operating at 60 -90°C.

Source: U.S. Department of Energy Hydrogen Programs www.hydrogen.energy.gov

While similar to batteries, internal combustion engines and generators, fuel cells have some key differences as outlined below:

  Fuel Cell Similarities Fuel Cell Differences
Batteries Converts chemical energy to electricity Does not store electricity and does not have to be recharged, but has to be refuelled
Internal
Combustion
Engine		 Uses a chemical process to convert energy from one form to another Does not utilize a combustive process, and when using hydrogen creates zero tailpipe emissions.
Generators Produces electricity Does not convert mechanical power to electricity.

Fuel cell vehicles are electric, similar to battery vehicles. Gaseous hydrogen is pumped into a tank in the car, similar to gasoline. The hydrogen is then fed into the fuel cell where it is electrochemically converted into electricity. There is no combustion and no emissions other than water vapour. The electricity generated is used to power the vehicle. A fuel cell is about two to three times more energy efficient than a gasoline engine.


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