Nonfluorinated polymer

In addition to Nafion-based catalyst layers, additional types have been developed, including CLs with different ion exchange capacities (lECs) [57,58] or with other hydrocarbon-type ionomers such as sulfonated poly(ether ether ketone) [58-60], sulfonated polysulfone [61,62], sulfonated polyether ionomers [63], and borosiloxane electrolytes [64], as well as sulfonated polyimide [65]. These nonfluorinated polymer materials have been targeted to reduce cost and/or increase operating temperature. Unfortunately, such CLs still encounter problems with low Pt utilization, flooding, and inferior performance compared wifh convenfional Nafion-based CLs. 

Roziere, J. and Jones, D. 2003. Nonfluorinated polymer materials for proton exchange membrane fuel cells. Annual Review of Materials Research 33 503-555. 

This chapter is divided into three main sections fluoropolymer synthesis, nonfluorinated polymer synthesis, and polymer characterization in C02. In the fluoropolymer synthesis section, solution, precipitation, biphasic, and continuous polymerizations will be described. Several examples of nonfluorinated heterogeneous chain-growth polymer syntheses will be followed by step-growth polymerizations. A brief summary of polymer characterization methods in C02 will conclude the chapter. 

Figure 10.6 Structures of nonfluorinated polymer electrolyte materials.

A large number of nonfluorinated polymers are now under investigation. Some of these activities have been reviewed in recent publications [165]. Approaches include the sulfonation of commercial polymers and the polymerization of new functionalized polymers. One of the first polymers chosen for sulfonation was polysulfone [166-174]. More recently the synthesis of stable polysulfones from sulfonated monomers has been explored [175]. 

The reaction of polymers with oxygen becomes less probable with decreasing polymer hydrogen content. Thus, fluoropolymers have higher thermal stabilities than nonfluorinated polymers with otherwise the same constitution. Aromatic and heteroaromatic substituents are even more thermally resistant. 

Table 7.2 shows the properties of BM-500B, the state of electrode paint and an example of the electrode properties. BM-500B is the first nonfluorine polymer to be practically applied to batteries as a binder for the positive electrode. BM-500B is designed to exert its excellent properties as a binder for positive electrodes by optimizing its components, their ratio, and mannfactnring conditions. 

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