**3.3 Gaskets**

Gaskets are sheets of rubbery polymer used to prevent leaking of reactant gases and coolant. They are carefully selected to be able to withstand the propellant of gaseous fuels, resist operating temperature up to 100°C, not affected by ambient

**231**

*Fuel Cells as a Source of Green Energy*

**3.4 The gas diffusion layers**

components are:

*3.5.1 The electrodes*

*3.5.2 The electrolyte (membrane)*

methanol concentration and temperature.

*DOI: http://dx.doi.org/10.5772/intechopen.89736*

**3.5 Membrane electrodes assemble (MEA)**

air humidity or moisture of reaction gases, non-corrosive by liquid acids, and also

Two pieces of a conductive material and they are representing important parts of the fuel cell. They are manufactured in a porous form using carbon fibers weaved into carbon papers or clothes [21]. Their major works are to transfer the reactants between the bipolar plates and the catalyst layers, assist the dissipation of the produced water and heat from the catalysts and protect them from corrosion [22].

A compact unit which is responsible for producing the output power of the fuel cells. Its thickness approaches a few hundred microns and consists of; the electrolyte, the two electrodes with their catalysts, with/without GDL [23]. These

As in any electric cell, the fuel cell has two electrodes that are cathode and anode. At these parts of fuel cell the chemical reactions which produce electricity occur. Therefore, the catalyst is required for each electrode. When hydrogen atoms enter a fuel cell at the anode, the catalyst strips them of their electrons in the oxidation process. The oxygen reduction occurs at the cathode. The electrodes that have a large active surface area of electrode to catalyst are regarded as a good electrode. The overall performance of the electrode should be stabile during operation time, and this can be satisfied by choosing a suitable catalyst for the specific electrode material, distribution the catalyst over the electrode uniformly, remove the produced excess heat and water, and most importantly for the best connection with the external electrical circuit.

The electrolytes are thin plastic-like or solid polymer membranes. Their main function is to pass the hydrogen positive ions from the anode to the cathode while completely block the free electrons from moving in this direction [18]. If the free electrons could pass through the electrolyte, they would hold up the chemical reaction. The filtration process is based on the semi-permeability of the membrane. There are several mechanisms of ions permeability through the membrane including absorption and adsorption, distillation, extraction, physical filtration, and stripping. The compositions of the electrolytes are perfluorosulfonic acids, which are Teflon-like fluorocarbon polymers that have side chains ending in sulfonic acid groups (–SO32–). Such acidic polymer electrolytes require water to conduct hydrogen ions. Therefore, the reaction gas (H2) in contact with the electrolyte must be saturated with water. The commercial name of Teflon based polymer electrolyte is Nafion [20]. It has a high ionic conductivity at 80°C, good thermal and chemical stability [24–27], and high chemical resistance. Its chemical chain is shown in **Figure 5** [28]. Fuel cells performances improve largely with increasing temperature to 90o C due to the decline in ohmic resistance of their electrolytes [29]. But at higher temperatures, the fuel cell will dry. Since Nafion ionic conductivity is strongly dependent on water content, the Nafion membranes will have an osmotic swelling problem and maybe potentially dissolve in methanol solution when increasing

withstand mechanical pressures resulting from prolonged operation [20].

air humidity or moisture of reaction gases, non-corrosive by liquid acids, and also withstand mechanical pressures resulting from prolonged operation [20].
