Proton-Conducting Analogues

The aim of this chapter is to provide a brief introduction into the vast field of solid alkali cation and proton conductors, considering also their Ag+- and Tl + -conducting analogues. More detailed information and an extensive bibliography can be found elsewhere [1-21]. The analysis of the relationships between transport properties, crystal structure and composition ofthese materials requires, initially, a formulation of the major classification principles and criteria. 

Li et al. [181] reported branched sulfonated poly(ether ether ketone)s (Br-SPEEK) using various amounts of l,3,5-ira(4-fluorobenzoyl)benzene as the branching agent. The structure of the Br-SPEEK is shown in Scheme 2.48. The proton conductivity and methanol permeability of the Br-SPEEK were measured and compared with the linear analogue and with Nation 117. 

In a further study, the researchers analyzed the proton conductivity and membrane stability of low lEC containing fluorinated block co-SPI membranes and compared their PEM properties with a corresponding random analogue [265]. The structure of the co-SPIs investigated is presented in Scheme 3.38. The authors observed much a higher value of proton conductivity for the block co-SPI membrane than for the random membrane, even though the same lEC values existed for both polymers. In particular, the... 

These polymers have been evaluated as membrane materials for fuel cell applications [84,85]. They have low methanol diffusion characteristics methanol diffusion coefficients for these membranes were found to be at least 12 times lower than that for Nafion 117 and 6 times lower than that for a cross-linked sulfonated polyphosphazene membrane [83,84]. Membranes were found to have lEC values between 1.17 and 1.47mequiv/g and proton conductivities between 10 and 10 S/cm. They appear to be superior to sulfonated polyphosphazene analogues [84,85]. 

Proton conducting ceramics are commonly based upon the perovs-kite structure type with the cerate and zirconate types being most prevalent. Initial studies focused on the SrCeOs- and SrZrOs-based materials. Uchida et al. demonstrated sizeable proton conductivity in each of these materials but due to concerns over the stability of these compositions attention shifted towards the Ba analogues. In these materials the key concern is their stability in CO2 containing atmospheres. 

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