Hydrocarbon polymers proton exchange membranes based

Proton Exchange Membranes Based on Hydrocarbon Polymers... 

Numerous works by other authors and our own research group describe the syntheses of new proton exchange membranes based on hydrocarbon polymers. The characteristics of these new materials, which determine their potential applications, are discussed in detail. A review of electrochemical properties, water uptake, and thermal stability makes possible a comprehensive understanding of the proton conduction mechanism and physical state of absorbed water in these systems. 

Fig. 6.2 Chemical structures of proton exchange membranes based on a hydrocarbon polymer backbone...

The heart of the PEM fuel cell is the proton exchange membrane, which transports protons from the anode to the cathode. The membrane also serves to separate the fuel and oxidant gas phases and electronically insulates the cathode from the anode. The most typical membrane is a sulfonated per-fluorinated polymer. The Nation family of membranes made by DuPont is representative of this class, and is based on a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, with the chemical structure represented in Figure 1.2. The sulfonic acid (SO3H) groups on the side chains allow the protons or other cations to "hop" from one acid site to another, in the presence of water. The exact mechanism of the proton movement is an area of significant research. An active area of research is the development of hydrocarbon-based... 

Over the last decade, several new proton exchange membranes have been developed. The new polymers in fuel cell applications are based mostly on hydrocarbon structures for the polymer backbone. Poly(styrene sulfonic acid) is a basic material in this field. In practice, poly(styrene sulfonic acid) and the analogous polymers such as phenol sulfonic acid resin and poly(trifluorostyrene sulfonic acid), were frequently used as polymer electrolytes for PEMFCs in the 1960s. Chemically and thermally stable aromatic polymers such as poly(styrene) [ 3 ], poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbony 1-1,4-phenylene) (PEEK) [4], poly(phenylenesulfide) [5], poly(l,4-phenylene) [6, 7], poly (oxy-1,4-phe-nylene) [8], and other aromatic polymers [9-11], can be employed as the polymer backbone for proton conducting polymers. These chemical structures are illustrated in Fig. 6.2. 

Abstract In this chapter, we discuss the proton conductivity and use of heteropoly acids (HP As) in proton exchange fuel cells. We first review the fundamental aspects of proton conduction in the HPAs and then review liquid HPA-based fuel cells. Four types of composite proton exchange membranes containing HPAs have been identified HPAs imbibed perfluorosulfonic acid membranes, HPAs imbibed hydrocarbon membranes, sol-gel-based membranes, and polymer hybrid polyoxometa-late (polypom)-based membranes. 

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