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The first working fuel cell was produced by Sir William Grove in 1842. The technology advanced slowly over the years but took a giant leap in the 1960s when General Electric produced the first practical fuel cell application for onboard electrical power for the Gemini and Apollo space capsules.
A fuel cell is an electrochemical energy conversion device that converts hydrogen and oxygen into electricity and heat. It is very much like a battery that can be recharged while power is drawn from it. Instead of recharging using electricity, however, a fuel cell uses hydrogen and oxygen.
A fuel cell consists of two electrodes, an anode and a cathode, separated by an electrolyte. Power is produced electrochemically when ions (charged particles) formed at one end of the electrodes with the aid of catalyst pass through the electrolyte. The current produced can be used for electricity.
 Diagram showing a proton exchange fuel cell using a polymer electrolyte membrane. Hydrogen is fed to the anode side of the fuel cell where the catalyst encourages the hydrogen atoms to release electrons and become hydrogen ions (protons). The electrons travel through an electric circuit as an electric current that can be utilized before it returns to the cathode side of the fuel cell where oxygen is added. At the same time, the protons diffuse through the membrane to the cathode, where the hydrogen atom is recombined and reacted with oxygen to produce water. |
The major difference between most fuel cells is the type of electrolyte. Electrolyte types include phosphoric acid, molten carbonate, solid oxide, and proton exchange membrane.
Phosphoric Acid
Phosphoric acid fuel cells are generally considered "first generation" technology. These fuel cells operate at about 200°C (400°F) and achieve 40%-45% fuel-to-electricity efficiencies on a lower heating value (LHV) basis.
Molten Carbonate
Molten carbonate technology has the potential to reach fuel-to-electricity efficiencies of 50%-60% LHV. Operating temperatures for molten carbonate fuel cells (MCFCs) are around 650°C (1,200°F), which allows total system thermal efficiencies up to 85% LHV in combined-cycle applications. MCFCs have been operated on hydrogen, carbon monoxide, natural gas, propane, landfill gas, marine diesel, and simulated coal gasification products.
Solid Oxide
Solid oxide fuel cells (SOFCs) operate at temperatures up to 1,000°C (1,800°F), which further enhances combined-cycle performance. A solid oxide system usually uses a hard ceramic material instead of a liquid electrolyte. The solid-state ceramic construction enables the high temperatures, allows more flexibility in fuel choice, and contributes to stability and reliability. As with MCFCs, SOFCs are capable of fuel-to-electricity efficiencies of 50%-60% LHV and total system thermal efficiencies up to 85% LHV in combined-cycle applications.
Proton Exchange Membrane
These cells operate at relatively low temperatures (about 200°F), have high power density, can vary their output quickly to meet shifts in power demand, and are suited for applications in which quick start-up is required (e.g, transportation and power generation). The proton exchange membrane is a thin plastic sheet that allows hydrogen ions to pass through it. The membrane is coated on both sides with highly dispersed metal alloy particles (mostly platinum) that are active catalysts. As shown in the diagram above, hydrogen is fed to the anode side of the fuel cell, where the catalyst encourages the hydrogen atoms to release electrons and become hydrogen ions (protons). The electrons travel in the form of an electric current that can be used before it returns to the cathode side of the fuel cell, where oxygen has been fed. At the same time, the protons diffuse through the membrane to the cathode, where the hydrogen atom is recombined and reacted with oxygen to produce water, thus completing the overall process.
For more information, visit the DOE Fuel Cells Web site.
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