3. Purification

For fuel cells to function properly and last a long time, they need pure hydrogen, with a degree of 3N (99.9%) or higher, and above all free of carbon monoxide (less than 20 ppm molar), hence the need to purify the gas produced by the methods described above. Several processes are available for this purpose, including membrane separation, cryogenics and, most commonly, selective adsorption using porous alumino-silicate materials.

• Membranes are barriers a few hundred nanometers to a few millimeters thick which, under the effect of a transfer force, may or may not allow certain components to pass through. Among existing membranes, inorganic, metallic or ceramic membranes, although the most expensive, tolerate the highest flows and are the most resistant (corrosion, pressure, temperature).

• Cryogenic separation...