Kinetic study of Nafion degradation by Fenton reaction

Abstract

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 (H2O2) and iron ions (Fe2+). The Nafion degradation kinetics were estimated by fluorine ion (F−) generation. The H2O2 and Nafion degradation reactions fit a pseudo-first-order rate constant. The values of the activation energy and frequency factor are 85kJmol−1 and 3.97×108s−1 for H2O2 decomposition in the presence of a Nafion film and 97kJmol−1 and 9.88×108s−1 for F− generation. The Nafion surface morphology became rough after reaction for 12h; small cracks, approximately 100μm in length, were observed at temperatures below 60°C. These cracks connected to make larger gaps of approximately 1mm at temperatures above 70°C. We also found a linear relationship between H2O2 consumption and F− generation. The rate constant is temperature dependent and expressed as ln(d[F−]/d[decomposed H2O2])=−19.5×103K−1+42.8. F− generated and H2O2 consumed along with the Nafion degradation conditions can be predicted using this relation.