Polyelectrolytes and protonic conductors

Our considerations above have laid emphasis on conduction by ions present by default or added as a separate ingredient to the polymer. Some polymers are, 

A prime need for a solid ionic conductor arises in the design of electrochemical fuel cells (Alberti and Casciola, 2001). Perhaps the most important type is the hydrogen fuel cell, shown diagrammatically in Fig. 8.5. Here the membrane which separates the two electrodes must be able to transfer protons efficiently. A material which combines the flexibility and toughness of a plastic with high protonic conductivity would be an ideal candidate. Prototype cells were successfully operated with membranes made from poly(styrenesulphonate), 

In the presence of water this polyelectrolyte is an excellent protonic conductor, although it suffers some degradation in a working fuel cell. Probably the most successful polyelectrolytes developed so far are based on perfluorinated polymers, the first of which was Nafion , with the structure  

One shortcoming of the perfluoro-based materials is their high cost, and this has led to the development of alternative proton-conducting electrolytes using 

Sulphonated PEEK, in its hydrated form, displays a conductivity as high as 5 fl 1m I even at 100 C, and the sulphonation is stable up to 250 C. 

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