Aromatic hydrocarbon ionomers

These findings are, more or less, applicable to the other aromatic hydrocarbon ionomers and useful to design the higher-order structure and properties of ionomer membranes. 

Solubility of Ionomers. Ionic bonding with metal ions decreases solubility in organic solvents (6,11). Commercial ionomers can generally be swollen by certain solvents such as aromatic hydrocarbons at elevated temperatures, but do not dissolve completely to give viscous solutions. Resistance to surface etching by oiganic solvents is high in most cases. 

Current membrane development focuses on perfluorinated ionomers, hydrocarbon and aromatic polymers and acid-base polymer complexes. Good recent reviews on membrane synthesis and experimental characterization can be found in this volume and for example in [23-29]. 

Several non-fluorinated alternative polymers have been proposed for DAFC, mainly based on sulfonated ionomers with an aromatic or aliphatic hydrocarbon skeleton [7], Kim and Pivovar [4] have reported the number of DMFC alternative membranes papers appearing in open hterature for years 1994—2004, showing that polyarylenes, polyvinyl alcohols, grafted and block polystyrenes copolymers, and polyimides were among the most studies polymer electrolytes. In view of the dramatic increase in the number of publications since 2005 (see Fig. 6.1), the trends have changed, as shown in Table 6.1, which sununaiized the publications in open literature for the period 2005-2012, as compared to the previous period. 

The mentioned disadvantages of PFI membranes induced many efforts to synthesize PEM based on hydrocarbon-type polymers and brought about the emergence of partially fluorinated and fluorine-free ionomer membranes as alternatives to Nafion membranes. Among them the membranes based on aromatic PEEK were shown to be promising for fuel cell application, as they possess good mechanical... 

Similar to pure hydrocarbon membranes discussed previously, both the aromatic rings and the SOj" groups are lost after the durability test (Yu et al. 2003). No preferential cleavage of sulfonic acid groups was observed. On the basis of XPS results, it also is found that chemical degradation during fuel cell operation occurs mainly on the hydrocarbon fraction of the radiation-grafted ionomer membranes (Nasef and Saidi 2002). Thus, the hydrocarbon fraction has less chemical stability than the fluorinated part. 

---