[updated 020901] Fuel Cells are a technology that generates electrical power from chemicals. Typically, the reaction is between hydrogen (often stored in some more convenient form such as methane or methanol) and Oxygen. The reaction product is water. Hydrogen and Oxygen are relatively light materials compared to materials like Lead and Cadmium used in conventional batteries. No electrolyte is needed in fuel cells although a charge transport layer may be present. A catalyst layer is often used to increase reaction rates. Fuel cells can achieve higher energy densities than batteries. Batteries are generally packaged as sealed or ventable units that contain the reaction chemicals and are often rechargeable. Fuel Cells on the other hand consume the reaction chemicals as fuel and exhaust the harmless reaction products. Fuel is added as needed.

Until recently, practical fuel cells have operated only at inconveniently high temperatures. Modern catalyzed cells are approaching room temperature operation -- a highly desirable characteristic in applications such as a laptop PC. There are problems to be overcome. For example, most fuel cells won't work if oriented upside down. They currently (2008) can not be scaled to the small size needed by portable devices such as cell phones. Current designs require venting and therefore can not operate under water. Fuel Cells may not be usable on aircraft because of the risk of fuel leaks through the vents. Technologies for safe refueling of consumer fuel cells are not yet in place.

Fuel cells have been used in exotic applications since the 1950s. For example, they are utilized in manned spaceflight where the reaction product (water) is itself a necessary resource. Fuel cells are cost competitive with gasoline generators in some applications, they are only now approaching practical use in portable devices such as computers. It is thought that once perfected and mass produced, they will offer substantially extended "battery" lives.

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