The proton exchange membrane fuel cell, PEMFC, takes its name from the special plastic membrane used as the electrolyte. Robust cation exchange membranes were originally developed for the chlor-alkali industry by DuPont and have proved instrumental in combining all the key parts of a fuel cell, anode and cathode electrodes and the electrolyte, in a very compact unit. This

membrane electrode assembly

(MEA), not thicker than a few hundred microns, is the heart of a PEMFC and, when supplied with fuel and air, generates electric power at cell voltages around 0.7 V and

power densities

of up to about 1 Wcm

electrode area. Thin gas-porous noble metal electrode layers (several microns to several tens of microns) on either side of the membrane contain all the necessary electrocatalysis, which drives the electrochemical power generation process. The membrane relies on the presence of liquid water to be able to conduct protons effectively, and this limits the temperature up to which a PEMFC can be operated

. Figure 4.1 shows a schematic of an MEA.