Aspects of the chemical degradation of PFSA ionomers used in PEM fuel cells

The chemical degradation of perfluorosulfonic acid (PFSA) membranes was studied both in-situ (during fuel cell operation) and ex-situ (by Fenton's test). During fuel cell operation, the degradation rate was quantified by monitoring the rate of fluoride release. The rate of degradation was found to be strongly dependent on operating conditions. Nuclear magnetic resonance (NMR) and mass spectrometry (MS) were used to identify degradation products other than fluoride generated during fuel cell operation. Strong similarities were found between the organic fragments generated from both the in-situ (fuel cell operation) and ex-situ (Fenton's test) degradation processes. The chemical structure of the fragment is consistent with that of the side chain on the PFSA ionomer used in the experiments. The implications of the existence of this product for the chemical degradation mechanism are discussed.