Fuel Cells

Definition:
A fuel cell is a device that continuously converts chemicals into direct current electricity through electrochemical reactions. In a typical fuel cell hydrogen gas combines with hydroxyl ions at one electrode to produce water and electrons. The electrons perform electrical work by flowing through an external circuit to the other electrode, where they recombine with oxygen and water to produce hydroxyl ions. The overall reaction is 2H2 + O2 -----> 2 H2O. The fuel cell differs from a battery in that its reactants must be supplied from an outside source. Fuel cells can theoretically convert fuel to electricity with nearly 100% efficiency. By contrast, burning fuel to produce steam for electricity is 40% to 50% efficient, and internal combustion engines are only 10% to 20% efficient.

History
The first attempt to obtain electricity directly from a fuel was probably made in 1802 by Sir Humphry Davy, who described a cell with a carbon anode and aqueous nitric acid as the cathodic reactant. The first hydrogen oxygen cell (reported 1839) was composed of two platinum strips immersed in acidified water; the upper part of one was exposed to hydrogen, the other to oxygen. Numerous attempts were made to develop efficient fuel cells that used carbon, because a galvanic cell that produced electrical energy directly from carbon and oxygen would be source of energy.

Types:
The most common fuel cells have used oxygen and hydrogen gas with potassium hydroxide as an electrolyte. The water produced by the reaction is carried out by circulating gases and condenses externally.

Considerable research has been done on fuel cell systems that use the direct oxidation of hydrocarbons. One promising model, the solid oxide (or monolithic) cell, passes fuel through a ceramic honeycomb structure that resembles corrugated cardboard. The solid oxide cell (so called because it contains electrolytes of yttrium-stabilized zirconium oxide) produces electrical energy from almost any hydrocarbon fuel, including gasoline. Moreover, it produce little pollution and maintains high efficiency oven at low operating levels.

Fuel cells are at present used chi efly in space vehicles or automobile and for limited military purposes. A 4.8-megawatt plat was put into operation in Tokyo in 1984, however, in the United States it is anticipated that similar electricity producing and cogeneration plants will eventually be online. Even cars may someday be powered by economical fuel cells.