The reactive oxygen species produced during the operation of an AEM fuel cell have hitherto not been detected during operation. Given the high pH, it is postulated that superoxide anion radicals (O2⋅-), as opposed to hydroxyl radicals, are primarily involved in the degradation progress. The objective of this study was to confirm O2⋅- formation during AEM fuel cell operation and to monitor in real-time the rate of O2⋅- generation in an operating fuel cell using in situ fluorescence spectroscopy.
1,3-diphenlisobenzofuran (DPBF) was chosen as the fluorescence probe, the sensitivity of which towards O2⋅- was evaluated by performing ex situ experiments in a semi-batch reactor. We demonstrate that the fluorescence intensity of this dye selectively decreased upon exposure O2⋅-. DPBF was then incorporated into an AEM (membrane was solution cast after mixing the dye with the casting solution), which was assembled into a fuel cell. O2⋅- generation in an operating AEM fuel cell was then monitored via in situ fluorescence spectroscopy using a bifurcated optical fiber probe, when the cell was operated in H2/O2 mode. To confirm the impact of O2⋅- on AEM degradation, independent experiments (without dye) were performed under identical conditions, under both H2/O2 and N2/N2 modes, and the ionic conductivity and ion exchange capacity were monitored to estimate degradation extent based purely on nucleophilic degradation. From our in situ fluorescence studies, we were able to independently estimate the rate constants and activation energy for oxidative AEM degradation in an operating AEM fuel cell.