ETFE-g-PSSA

Proton conductivity as a function of lEC for ETFE-g-PSSA = polyethylenetetrafluoroethylene-gra/t-polystyrene sulfonic acid, BAM membrane = substituted poly(trifluorostyrene) sulfonic acid, SPEEK = sulfonated poly(ether ether ketone) and Nafion. (From Peckham, T. J. et al. 2007. Journal of Materials Chemistry 17 3255-3268, and Dolye, M. et al. 2001. Journal of Physical Chemistry B 105 9387-9394.)... 

In the case of Nafion, a similar situation occurs. There is a sharp increase in proton conductivity and proton concentration as a function of water content followed by a decrease at A > 20. At these higher water contents, Nafion undergoes a similar dilution of proton concentration per BAM membrane in conjunction with a lower mobility value versus ETFE-g-PSSA. However,... 

Examples of radiation-grafted PEMs poly(ethylene-flZf-tetrafluoroethylene)-gra/f-poly(sty-rene sulfonic acid) (ETFE-g-PSSA), 30 PVDF-g-PSSA, 31 and poly(tetrafluoroethylene-co-hexafluoropropylene)-g-PSSA (FEP-g-PSSA), 32. 

Scheme 2 Chemical structures of a poly(perfluorosulfonic acid) b sulfonated polystyrene (SPS) c sulfonated polystyrene-fc-(ethylene-co-butylene)-fc-sulfonated polystyrene (SSEBS) d sulfonated polystyrene-fc-(isobutylene)-fc-sulfonated polystyrene (SSIBS) e poly(ethylene-co-tetrafluoroethylene)-g-polystyrene sulfonic acid (ETFE-g-PSSA) f poly(vinylidene fluoride)-g-polystyrene sulfonic acid (PVDF-g-PSSA) g poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether)-g-polystyrene sulfonic acid (FEP-g-PSSA) h sulfonated trifluorostyrene-trifluorostyrene copolymer (PTFSSA)...

Values of proton conductivity of ETEE-g-PSSA, Nafion , PTFSSA, and BPSH membranes are strongly dependent on EW (Fig. 14a). The conductivity of Nafion and PTFSSA membranes maximizes at intermediate EWs, while the conductivity of ETFE-g-PSSA and BPSH membranes increases with decreasing EW. ETFE-g-PSSA membranes possess an exceptionally high conductivity. Compared to ETFE-g-PSSA membranes, a moderate conductivity can be achieved for Nafion , PTFSSA, and BPSH membranes by adjusting the EW of the membrane. However, based on the conductivity-EW relationship for SSEBS membranes, the maximum conductivity obtained is only 0.05 S cm and this is much lower than that of other membranes. 

For Nation membranes, a linear relationship between conductivity and ionic concentration is reahzed. The [H ] of the ETFE-g-PSSA membranes is comparatively larger than those of PTFSSA and SSEBS membranes, and similar to Nation . However, the water content and A. for ETFE-g-PSSA mem-... 

Proton diffusion coefficients for ETFE-g-PSSA membranes (Scheme 2e) have been calculated and compared to those of Nafion 117 (Fig. 27) [189] as well as PTFSSA (Scheme 2h) [190]. Fully hydrated ETFE-g-PSSA and PTFSSA membranes exhibit much higher proton diffusion coefficients than hydrated Nafion 117 due to their high water content. This is in agreement with the higher conductivities observed for fully hydrated ETFE-g-PSSA and, in general, PTFSSA membranes (Fig. 14). However, when proton diffusion coefficients are compared where the three polymer series overlap (e.g., Xy = 0.1-... 

Fig. 27 Proton diffusion coefficients of ETFE-g-PSSA (Scheme 2e) and Nafion 117 membranes as a function of water volume fraction, Xy...

Scott et al. [56] tested the performance of radiation-grafted ElEE-g-PSSA membranes in comparison with Nafion in DMEC (90°C, 2M MeOH, and air). The ETFE-g-PSSA membranes showed comparable performance values with Nafion 117, especially with low current densities. 

Hatanaka et al. [92] prepared and tested the performance of ETFE-g-PSSA membranes in DMFC. These membranes were prepared by preirradiation of ETFE film (120 am) from y-radiation followed by styrene grafting and subsequent sulfonation. The membranes with degrees of grafting exceeding 30% displayed better transport properties, i.e., higher ionic conductivity and lower methanol permeation, compared with Nafion membranes. However, the PEM fuel cell performance of these membranes was found to be inferior to that of Nafion. The authors attributed such behavior to the poor bonding of the electrodes to the membrane surface in the MEA. 

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