- Protons exchange membrane
- Phophoric acid fuel cells
- Molten carbonate fuel cells
- Solid oxide fuel cells
Fuel cells offer distributed modular generation, high efficiency, and low environmental impact. Like a battery, a fuel cell directly converts chemical energy of reactants into low voltage direct current electricity. Unlike a battery, however, a fuel cell uses externally-stored fuel for its reactants.
To date fuel cells have been used primarily in space craft, but their potential for very high efficiencies (approximately 70 percent), low to virtually non-existent emissions (some versions operate with no emissions but carbon dioxide and water), ability to operate on a wide variety of fuels, modularity, and simple operational requirements make them an extremely attractive option for a variety of applications, including utility generation, industrial power, military applications, and a power source for long-range electric vehicle. Fuel cells are an important contender to serve as the power source for new clean vehicles being developed by the PNGV consortium.
In military applications, fuel cells offer a variety of advantages including low detectability with a low noise and infrared signature, low maintenance requirements, and high energy densities in remote applications. For instance, fuel cells could prove an alternative to advanced batteries in a variety of tactical power sources. As such, they contribute to the ability of Special Operations Forces to operate in a variety of environments.
The United States is the overall world leader across a wide range of fuel cell technologies but Japan is a very strong competitor in some segments. A great deal of U.S. fuel-cell technology was initially acquired from cooperative ventures and extended significantly by Japanese firms.