What Is a Fuel Cell?
A fuel cell is an electrochemical device that converts the energy of chemical reactions directly to electricity. Fuel cells bypass the chemical energy to heat to mechanical energy to electrical energy conversion stages needed for conventional electricity production. This results in much greater efficiencies.

How Does a Fuel Cell Work?
Fuel cells work by selectively allowing one reactant gas (usually oxygen from air) to diffuse through a thin membrane and react with another reactant gas, such as hydrogen. As the first reactant gas diffuses through the membrane, it picks up a charge, becoming ionized. Upon reaction, it releases the charge. If both sides of the membrane are connected to a load source, the charge will flow, creating electricity.

How Are Fuel Cells Classified?
Fuel cells are classified by the type of membrane, called an electrolyte, which separates the reactants. For example, solid oxide fuel cells have a solid oxide ceramic membrane. Molten carbonate fuel cells use a carbonate salt molten liquid electrolyte to separate the reactant gases. Polymer electrolyte fuel cells have a polymer membrane as the electrolyte.

Benefits

• High efficiency
• Virtually no gaseous emissions (SO_x, NO_x, or air toxic metals)
• No combustion needed
• Quiet operation
• No moving parts in the energy converter
• Fuel flexible
• Both high- and low-temperature fuel cells can be used for different applications
• Unattended or remote operation
• Modular design can be used to match size with performance requirements
• Demonstrated endurance and reliability

In summary, fuel cells generally have higher conversion efficiencies and no moving parts (thus greater reliability) and use fuels that are in great supply (hydrogen and oxygen). Moreover, fuel cells are far more environmentally friendly than conventional energy technologies, emitting only water vapor in many cases.

Fuel Cell Applications
Since fuel cells can deliver the same high efficiency for both small and large power systems, they are expected to penetrate the small power systems energy market first.

• Fuel cells will make it possible to economically generate electricity at remote locations, reducing dependence on large central power generating plants.
• Portable backup power supplies are being developed to take advantage of the fuel cell's high efficiency, quiet operation, and high reliability.
• At twice the efficiency of internal combustion engines, fuel cells are expected to penetrate the vehicular market in just a few short years. Trucks, trains, submersibles, and passenger vehicles are expected to be some of the first markets employing fuel cells in large quantities.
• Even the military is enthusiastic about fuel cells. Fuel cells are being developed to power small weapons systems. Fuel cell-powered tanks and personnel carriers could travel in complete silence, with almost no infrared signature.