Polymer electrolyte membrane ionomers with sulfonic acid

Polymer electrolyte fuel cells (PEFCs) have attracted much interest as one of the most promising nonpolluting power sources capable of producing electrical energy with high thermodynamic efficiencies. The key element of PEFCs is a polymer electrolyte membrane (PEM) that serves as proton conductor and gas separator [1, 2, 3,4], The membrane commonly employed in most PEFC developments is based on Nafion, which represents a family of comb-shaped ionomers with a perfiuorinated polymeric backbone and short pendant (side) chains having sulfonic acid end groups... 

Polymer electrolyte fuel cells (PEFCs) are unique in that they are the only variety of low-temperature fuel cell to utilize a solid electrolyte. The most common polymer electrolyte used in PEFCs is Nafion , produced by DuPont, a perfluorosulfonic ionomer that is commercially available in films of thicknesses varying from 25 to 175 pm. This material has a fluorocarbon polytetrafluoroethylene (PTFE)-kbone with side chains ending in pendant sulfonic acid moieties. The presence of sulfonic acid promotes water uptake, enabling the membrane to be a good protonic conductor, and thereby facilitating proton transport through the cell. This chapter reviews PEFC development, structure, and properties and presents an overview of PEM technology to date. 

Solid Polymer Electrolyte The most common solid polymer electrolytes consist of a hydrophobic and inert polymer backbone which is sulfonated with hydrophilic acid clusters to provide adequate conductivity as discussed in Chapter 5. In order to ensure adequate performance, some membrane hydration is required. However, excess water in the electrodes can result in electrode flooding, so that a precarious balance must be achieved. Modern perflourosulfonated ionomer electrolytes for H2 PEFCs are 18-25 xm thick with a practical operating temperature limit of 120°C, although PEFC operation is rarely greater than 90°C due to excessive humidity requirements and operational low lifetimes. 

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