Perfluorosulphonic acid polymer

Fig. 13.2 Structure of perfluorosulphonic acid co-polymer (Nation ). The Yeager Three Phase Model, based on a three-phase clustered system with interconnecting channels within the polymer. (a) Fluorocarbon backbone, (b) interfacial region of relatively large fractional void volume containing some pendant side chains, some water and sulphate groups, (c) clustered regions...

Yeo, R.S., Dual cohesive energy densities of perfluorosulphonic acid (Nafion) membrane, Polymer, 21, 432, 1980. 

Dupont de Nemours) or analogous perfluorosulphonic acid membranes have been the dominating choice. The structure of the repeat structure of the polymer fluorocarbon backbone and a side chain with sulphonic acid ends upon which Nafion is based is shown in Fig. 3.42 (the commercial product is sold with various thicknesses and dimensions denoted by a number code such as "Nafion-117", related to non-SI units). The membranes should have high protonic conductivity, low gas permeability and, of course, a suitable mechanical strength and low temperature sensitivity. 

Abstract This chapter describes the use of molecular dynamics (MD) simulations to understand structure and transport processes in polymer electrolytes for energy storage and conversion applications. For batteries, the polymer electrolytes studied with MD techniques have generally been of poly(ethylene oxide) (PEO)-type, while the fuel cell polymer electrolytes have been perfluorosulphonic acid (PFSA) membrane materials. The MD methodology, its benefits and its limitations are explained in the chapter, together with a review of some significant MD studies of polymer electrolytes. 

Polymer electrolytes for fuel cells perfluorosulphonic acid systems... 

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. 

Possibly one of the most complex deliberately designed of all polymer products is the family of membranes described by Seko for the selective passage of sodium (Na+) ions and repulsion of hydroxide ions in a chlorine cell. These perfluorocarboxylic acid membranes are claimed to represent an improvement on the Dupont Nafion class of perfluorosulphonic membranes designed for the same purpose, in that CF/OH" segregation is practically complete. Industrially, the implications for chlorine and caustic soda technology are profound. 

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