Polymer electrolyte fuel cell cathode side Applications

The polymer electrolyte membrane fuel cell (PEMFC) also known as proton exchange membrane fuel cell, polymer electrolyte fuel cell (PEFC) and solid polymer fuel cell (SPFC) was first developed by General Electric in the USA in the 1960 s for use by NASA in their initial space applications. The electrolyte is an ion conducting polymer membrane, described in more details in Section 2.2. Anode and cathode are bonded to either side of the membrane. This assembly is normally called membrane electrode assembly (MEA) or EMA which is placed between the two flow field plates (bipolar plates) (Section 2.5) to form what is known as stack . The basic operation of the PEMFC is the same as that of an acid electrolyte cell as the mobile ions in the polymer are or proton. 

As is the case with fuel cells, depolarized cathodes have been considered for years but have not yet found wide commercial use in the chlor-alkali indusby. Reports of work in the 1970s and 1980s [117,118] described the use of solid-polymer electrolyte systems. Microporous electrodes are necessary for electrical continuity in these cells, and the cathode reaction takes place in the interior of the gas-diffiision electrode. Operating deficiencies include the gradual penetration of gas channels by caustic solution and the possibility of bulk flow of catholyte into the gas side of the electrodes. Section 17.2.2.2 describes more recent work that addresses these deficiencies. The first conunercial applications are beginning to appear. 

The polymer electrolytes used for low-temperature proton exchange membrane fuel cells (PEMFCs) are fundamentally different from the polymer electrolytes used in batteries. Here, the polymer is a medium for a solvent, normally water, and it is mainly in the solvent that ion transport occurs. The polymer serves several functions, of which the most important is to provide mechanical stability and electrode separation in the fuel cell application. Since the fuel cell needs proton transport from the anode to the cathode, the polymer also contains proton donating groups, often sul-phonic acid (-SO3H). The prototype PEMFC membrane materials have been perfluorosulphonic acids (PFSAs), of which the most established membrane material is Nafion (Fig. 8.8). These consist of hydrophobic teflon -CF2-CF2- backbones, with fluorinated hydrophilic and acidic side-chains for Nafion -0CF2CF(CF3)0CF2Cp2S03H. 

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