Kinetic study of Nafion degradation by Fenton reaction

摘要

To predict the durability of polymer electrolyte membranes in fuel cells, the degradation reactions of Nafion 117 films were studied as oxidation reactions with hydroxyl radicals as oxidation accelerators. The radical species were generated by the Fenton reaction between hydrogen peroxide (H_2O_2) and iron ions (Fe~(2+)). The Nafion degradation kinetics were estimated by fluorine ion (F~-) generation. The H_2O_2 and Nafion degradation reactions fit a pseudo-first-order rate constant. The values of the activation energy and frequencyfactorare85kjmol~1 and 3.97 x 108s~' for H_2O_2 decomposition in the presence of a Nafion film and 97 kj mol~(-1) and 9.88 x 10~8 s~(-1) for F~- generation. The Nafion surface morphology became rough after reaction for 12 h; small cracks, approximately lOOμm in length, were observed at temperatures below 60 ℃. These cracks connected to make larger gaps of approximately 1 mm at temperatures above 70 ℃ We also found a linear relationship between H_2O_2 consumption and F~- generation. The rate constant is temperature dependent and expressed as ln(d[F-]/d[decomposed H-2O-2]) = -19.5 x 1O~3K~(-1) +42.8. F~-generated and H_2O_2 consumed along with the Nafion degradation conditions can be predicted using this relation.