FUEL CELL

"A device that converts chemical energy into electrical energy. It is different from a battery in that the energy conversion continues till fuel and oxidizing agent are fed to the fuel cell; that is, in principle indefinitely. (A battery is manufactured with a limited amount of chemicals, and it is exhausted when all the chemicals have reacted.) It is a galvanic cell, where spontaneous chemical reactions occur at the electrodes. The fuel is oxidized at the anode, and the oxidizing agent (almost always oxygen or air) is reduced at the cathode. Presently, the most commonly used fuel is hydrogen. More conventional fuels (e.g., gasoline or natural gas) must be converted (""reformed"") into hydrogen before they can be utilized in a fuel cell. Fuel cells that can burn hydrocarbon fuels directly are in the development stage. Some fuel cells employ an aqueous solution as electrolyte, that can be either acidic or basic (alkaline), or an ion-exchange membrane soaked in aqueous solution can act as the electrolyte (see PEM) these fuel cells operate at relatively low temperatures (from room temperature to not much above the boiling point of water). Some fuel cells employ molten salts (especially carbonates) as electrolytes and have to operate at many hundreds of oC temperature. Others employ ionically conductive solids as electrolyte and must operate close to 1000 oC. "