Perfluorinated sulfonic acid membrane chemical degradation

Inaba M (2009) Chemical degradation of perfluorinated sulfonic acid membranes. In Buechi EN, Inaba M, Schmidt TJ (eds) Polymer electrolyte fuel cell durability. Springer, New York... 

Chemical Degradation of Perfluorinated Sulfonic Acid Membranes... 

Xie, T., Hayden, C., Olson, K. and Healy, J. 2005. Chemical degradation mechanism of perfluorinated sulfonic acid ionomer. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 20-23, abstract 24. 

Before discussing membrane chemical degradation in detail, the factors governing the degradation mechanism must be identified. Among three major types of membrane materials, hydrocarbon, partially fluorinated, and perfluorinated ionomers, perfluorinated sulfonic acid (PFSA) is the most widely used membrane material owing to its high chemical stability (Schiraldi 2006). 

Fig. 3 Impact of RH on the chemical degradation rate of perfluorinated sulfonic acid (PFSA) membranes. All tests employed Nafion 112 with 0.4 mg Pt cm per electrode and were conducted with HyO at 95 C, 300kPa, and 525 seem gas flow (Liu et al. 2006)...

In perfluorinated ionomers, a PTFE-based polymeric backbone offers chemical stability from the radical species or acid-base, which causes hydrolytic degradation of the polymer chain. Ionic conductivity is provided by pendant acidic moiety in carboxylate or sulfonate form. There are some reports on perfluorinated carboxylic acid (PFCA) materials, most of which are derived from Nafion [26-29]. However, PFCA is not suitable for fuel cell application due to its low proton conductivity. Perfluorosulfonic acid (PFSA) is the most favored choice among not only perfluorinated membranes but all other ionomers in fuel cell applications. Sulfonic acid form of Nafion is a representative PFSA and thus has been intensively studied since 1960s. Reported chemical structure of Nafion membrane is given in Fig. 13.8. 

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