Colorimetric method for the determination of fluoride emission rates in polymer electrolyte fuel cells

The chemical degradation of the membrane leads to the premature end of the life of polymer electrolyte fuel cells (PEFCs). Hydrogen peroxide is a promoter of ionomer degradation, which can occur at the anode side and cathode side at lower or higher current densities, respectively [1,2,3,4,5]. Free radicals of hydrogen peroxide attack the side chains and the backbone of Nafion®, which leads to fluoride and fluorine emissions into the effluent water. Impurities in reactant gases are another source of chemical degradation of the membrane [6, 7]. Accurate determination of the fluorine emission rates indicates how much ionomer has been degraded.

A PEFC with an electrode area of 25 cm² was subjected to a JRC stress test [8]. After a certain number of cycles, comprehensive electrochemical characterizations were performed and effluent water samples were taken. Polarization curves and electrochemical impedance spectra were recorded to investigate the performance losses as well as the changes due to membrane degradation. In addition, linear sweep voltammetry measurements were performed to investigate the hydrogen cross-over current and the thinning of the membrane.

The effluent water was analyzed using a UV-vis spectrometer developed by AiDEXA GmbH. Zr(IV)-SPADNS2 [9] was added to the water samples and the absorption spectra were recorded which was used to determine the fluorine concentration. The results were correlated with the electrochemical measurements to obtain information on the power loss to a given amount of degraded membrane. These results can be used for lifetime estimates.

This research is performed under the projects B.GASUS (FFG grant number 884368) and HyLife (K-Project HyTechonomy, FFG grant number 882510), which are supported by the Austrian Research Promotion Agency (FFG).

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