Fuel cells generate electricity from a simple electrochemical reaction in which oxygen and hydrogen combine to form water. There are several different types of fuel cell but they are all based around a central design which consists of two electrodes, a negative anode and a positive cathode. These are separated by a solid or liquid electrolyte that carries electrically charged particles between the two electrodes. A catalyst, such as platinum, is often used to speed up the reactions at the electrodes.
Fuel cells are classified according to the nature of the electrolyte. Each type requires particular materials and fuels and is suitable for different applications. The article below uses the proton exchange membrane fuel cell to illustrate the science and technology behind the fuel cell concept but the characteristics and applications of the other main designs are also discussed.