Ionic conductivity early developments

In a solid polymer electrolyte, such as used in the PEFC, ion mobility is a result of an electrolyte solution integrated into an inert polymer matrix. Early electrolyte membranes developed for the United States space program consisted of treated hydrocarbons, which resulted in poor longevity due to the relatively weaker hydrocarbon bonds [3]. Most modem solid electrolytes are perflourinated ionomers with a fixed side chain of sulphonic acid bonded covalently to the inert, but chemically stable, polymer polytetrafluoroethylene (FIFE) stracture. As a result, the membrane consists of two very different sub-stractures 1) a hydrophilic and ionically conductive phase related to the bonded sulphonic acid groups... 

There are some who see this equation as indicative that a whole different approach to conductance theory might be waiting in the wings, as it were. As the concentration increases, the idea of an ionic atmosphere becomes less useful and one might start at the other end, with ideas used to treat molten salts (Chapter 5), but in a diluted form. This would repeat the history of the theory of liquids which, in the early part of this century, was derived from the treatment of very compressed gases but later seemed to be more developable from modifications of how solids are treated. 

Subsequent findings that even conventional ionic solids, such as sodium chloride, have measurable conductivities that are not electronic stimulated the development of theories for ionic motion in solids. Early in this century, Ioffe introduced the concept of interstitial ions and vacancies (see Defects in Solids), which was the starting point of the theory of defects. Frenkel and Schottky used these theories to develop their classic mechanisms to explain how electricity can be conducted through ionic solids by the flow of ions (see Frenkel Defects, Schottky Defects) They proposed that ionic solids are not perfect, with every lattice site occupied by its appropriate ions, but contain defects in which either ions... 

Perovskite related cathode materials have been shown to possess levels of ionic and electronic conductivity comparable to existing perovskite cathode materials. The development of these new cathodes is in the very early stages and significant research is required before these can compete with the established Lai.xSrxCoOs.g (LSC) and Lai.xSrxMnOg.g (LSM) based cathodes. However, one of the main advantages offered by these materials is the prospect of fast surface exchange and ionic diffusion at temperatures considerably lower than the established candidate materials thus enabling development of low temperature SOFC devices. 

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