Ex-situ measurement of chemical membrane degradation using photometry

Despite the critical role that degradation of the perfluorinated sulfonic acid (PFSA) membrane plays in polymer electrolyte fuel cells (PEFCs), it can so far not be reliably and quickly detected through in-situ characterization methods. To complement in-situ, ex-situ measurement methods are available and can partially be conducted while the cell is in operation. Polymer fragments and fluoride from the degradation of the membrane can be found in the effluent water, leaving the fuel cell. While it is possible to measure membrane degradation outside of the cell, the existing methods have drawbacks or prerequisites on their own. Therefore, the measurement of membrane degradation is proposed using fluoride as the indicator with a zirconium complex (zirco-nyl-2-(4-sulphophenylazo)-1,8-dihydroxy-3,6-naphtalene-disulfonic acid), referred to as SPADNS. The interaction between the complex and fluoride is measured using a photometric method and the quantification is based on the color and intensity shift, caused by the interaction of fluoride with the complex. We find that this method can quantify the fluoride concentration correctly. A comparison to a fluoride-sensitive electrode is conducted and validated using a Bland–Altman correlation. The photometric method also requires smaller sample quantities, reducing the required sample amount to 0.9 ml compared to the 5 to 15 ml required for fluoride-sensitive electrode measurements. Measurement times are also reduced to 60 s per sample, reducing the needed time by more than a factor of 10, compared to measurements with an electrode or through ion chromatography. With this, it is possible to get a complementary information about the state of health of the membrane faster and quantify chemical degradation ex-situ. Chemical membrane degradation can be characterized reliably and in a reasonable timeframe using the proposed method.