Proton exchange membrane fuel cells Purification

In fuel cells systems, as reported in recent patents [13,14], membranes wUl be present not only as PEM (proton-exchange membrane), which allows protons to pass from the anode to the cathode where they are combined with oxygen and electrons to produce water, but also for the production and purification of the H2 (Figure 43.3). This system provides a C02-selective membrane process for the purification and water gas shift reaction of a reformed gas, generated from on-board reforming of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, or natural gas, to hydrogen for fuel cell vehicles. 

Separation of gas and liquid mixtures using polymer membranes has now become accepted as a unit operation in many chemical process flows. Most barrier coatings are applied as dense films, but for applications such as gas separation a very thin layer is needed so that gas diffusion can take place in a sufficiently short time period. Water purification membranes are usually a thin, dense polyamide film on a porous support forming a composite membrane. Fuel cell membranes in contrast involve dense films of proton exchange materials. In many cases, control of phase separation and understanding the underlying thermodynamic processes are key elements in successful membrane constmaion. 

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