Degradation of nafion membranes

Chen C, Fuller TF (2009) The effect of humidity on the degradation of Nafion membrane. Polym Degrad Stabil 94 1436-1447... 

L. Ghassemzadeh, K.-D. Kreuer, J. Maier, K. MueUer, Chemical degradation of NAFION membranes under mimic fuel cell conditions as investigated by sohd-state NMR spectroscopy, J. Phys. Chem. C 114 (2010) 14635—14645. 

Kodama, K., Miura, F., Hasegawa, N., Kawasumi, M., Morimoto, Y. (2005) Degradation of Nafion membranes in hydrogen peroxide. In 208th Electrochemical Society National Meeting, Los Angeles, CA, October 2005, Paper 1185. 

Ghassemzadeh, L., Kreuer, K.-D., Maier, J., MiiUer, K., Chemical degradation of Nafion membranes under mimic fuel ceU conditions as investigated by solid-state NMR spectroscopy./ Phys. Chem. C2010,114(34), 14635-14645. 

PEMFCs generally operate at temperatures <100°C. PFSA-based polymer ionomer membranes like Nafion, Gore, Aciplex, and Flemion are not significantly affected by temperatures up to 150°C where most of the water is lost and membranes may suffer irreversible dry out. Chemical degradation of these membranes in the form usually starts with the loss of sulfonate groups at over 220°C [7]. 

Chen, C., Levitin, G., Hess, D. W., and FuUer, T. F. 2007. XPS investigation of Nafion membrane degradation. Journal of Power Sources 169 288-295. 

Figures 10.18 through 10.20 show fluoride emissions from CCMs in hydrogen peroxide. Both the original and the modified CCM had increasing fluoride emissions over time, but the modified CCM emitted more. Fluoride in a fuel cell solution can originate from the degradation of Nafion in the catalyst layers and/or in the Nafion membranes (Li, 2010).

Nam et al. [26] used organic-inorganic nanocomposite material like Nafion/ poly(phenyhnethyl silsequioxane, PPSQ). Incorporation of PPSQ improved initial degradation temperature of Nafion membrane and increased the crystallinity of the recast composite membrane. The membrane was reported to have lower methanol permeability as compared with bare Nafion due to interruption of organic filler. 

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. 

Sun, L., Thrasher, J. S., Studies of the thermal behavior of Nafion membranes treated with aluminum(in). Polym. Degrad. Stab. 2005, 89 (1), 43 9. 

Early experimental versions of Nafion within the context of chlor-alkali cells consisted of SO2F precursor forms that were first reacted on only one side with ethylenediamine (EDA) before the conversion of the remainder of the membrane to the sulfonate form took place. The result was a well-defined stratum of sulfonamide cross-links, that were formed upon heating after reaction, that served to reduce swelling at the catholyte interface, which, in turn, reduced OH back migration. However, these EDA-modified membranes proved inadequate in chlor-alkali cells due to the chemical degradation of these cross-links... 

The properties of Nafion at freezing temperatures can be quite relevant, for example, within the context of fuel cells in vehicles with regard to cold-starting, as well as the degradation of membrane/electrode assemblies due to the freezing of in situ water. 

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