A fuel cell combines hydrogen and oxygen to produce electricity. The basic principle of the fuel cell is illustrated in the figure below. The core of each fuel cell consists of an electrolyte and two electrodes. At the negative anode, a fuel such as hydrogen is being oxidized, while at the positive cathode, oxygen is reduced. Ions are transported through the electrolyte from one side to the other. The type of electrolyte determines the temperature window of operation. This window of operation in its turn determines the catalysts that can be used, and the purity of the fuel to be used. The theoretical open circuit voltage of a hydrogen-oxygen fuel cell is 1.23 V at 298 K, in practice it is around 1 V at open circuit. Under load conditions, the cell voltage is between 0.5 and 0.8 V.

Fuel Cell Principle