Fuel cells can make an 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. Every type needs particular materials and fuels and is suitable for any 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. Proton Exchange Membrane Fuel Cells (PEMFC)
The hydrogen ions permeate across the electrolyte to the cathode, while the electrons flow through an external circuit and provide power. Oxygen, in the form of air, is supplied to the cathode and this combines with the electrons and the hydrogen ions to produce water. These reactions at the electrodes are as follows:
Anode: 2H24H+ + 4e-
Cathode: O2 + 4H+ + 4e- 2H2O
Overall: 2H2 + O22H2O + energy
PEM cells operate at a temperature of around 80°C. At this low temperature the electrochemical reactions would normally occur very slowly so they are catalysed by a thin layer of platinum on each electrode.
