Proton Electrolyte Membrane (PEM) fuel cell

A Proton Electrolyte Membrane (PEM) fuel cell consists of two bipolar plates (anode and cathode), a Membrane Electrode Assembly, and Diffusion Media. These elements when connected to an electric load produce DC power. Hydrogen fuel cells need two elements to generate power, oxygen from the air, and hydrogen. The hydrogen and oxygen react through the membrane assembly to produce the electric power. The only by-product of the fuel cell is pure water.

The US DOE Hydrogen Program emphasizes polymer electrolyte membrane (PEM) fuel cells in passenger vehicles.Liquid fuels are also attractive for portable and remote fuel cell applications due to their ease and convenience of handling. Family of portable PEMFC systems, rated at 250 We, that incorporate a compact methanol/water reformer and integral hydrogen purifier targetting both military and commercial applications are also under development. Efficiency for a PEM cell reaches about 40 to 50 percent. An external reformer is required to convert fuels such as methanol or gasoline to hydrogen. Currently, demonstration units of 50 kilowatt (kw) capacity are operating and units producing up to 250 kw are under development.

Fuel cells are grouped together in a "fuel cell stack." This stack then becomes the engine in a fuel cell automobile, or the power generator for electricity.