Radical-induced degradation mechanism of perfluorinated polymer electrolyte membrane

The degradation mechanism induced by radicals was investigated for Nafion^®-117 by solution analysis. Nafion^® was exposed independently to three kinds of radicals, OH, H and O₂⁻ which were produced separately by γ-irradiation. Based on the eluted elements, the scission site in the membrane was analyzed. The results showed that the scission site was classified into two and these locations were closely relating to oxidative and reductive reactions. The decreasing rate of proton conductivity was more significant under the influence of reductive radicals. The progression of the unzipping reaction of main chain was suggested to be initiated by the production of tertiary carbon radical by reductive radicals such as H and O₂⁻ with the aid of OH. The structural degradation such as collapse of cluster and the cluster decomposition as well as the performance degradation was found to be initiated by such reductive radicals.     

Detection of OH radicals as the effect of Pt particles in the membrane of polymer electrolyte fuel cells

The formation of OH radicals (OH) for polymer electrolyte fuel cell (PEFC) was investigated with a homemade test cell by means of a fluorescence probe method for several kinds of membrane electrode assembly (MEA) consisting of Nafion. After 12-h operation under open circuit condition, OH was detected at both the anode and the cathode sides but the amount was much larger for the anode side. The formation of OH considerably depended on the amount of Pt/C catalyst loaded in the MEA. Dispersion of Pt particles in Nafion membranes increased the OH formation, but Pt ions did not. Based on the results, the formation mechanism was discussed.