Observation of Membrane Degradation by In-Situ and Ex-Situ Electron Paramagnetic Resonance

The degradation of fuel cell membranes was investigated with perflourinated and with polyaromatic materials. Since radical mechanisms are thought to be responsible for damaging the components in a working fuel cell, •OH radicals were generated by cleavage of hydrogen peroxide by UV light, by heat, and using Fenton's reagent. Aiming at the development of accelerated ageing tests for membranes, measurements of radical species were performed by electron paramagnetic resonance ex-situ with monomer and polymer solutions and with membranes, and in-situ on catalyst coated membranes. No signals indicating •OH attack on Nafion were detected, in contrast to all polyaromatic membrane materials. Nevertheless, in-situ spin trap measurements with Nafion reveal strong signals which formally belong to trapped H atoms but are not related to degradation. Relative to the Faraday electrons from the electrochemical reaction they appear on a ppm level.