In-situ and ex-situ monitoring of membrane degradationin polymer electrolyte fuel cells using advanced analytical techniques

Fuel cells convert chemical energy directly into electrical energy at high efficiency and without CO2 emissions. The degradation products in the exhaust, caused by the chemical degradation of the membrane of polymer electrolyte fuel cells (PEFCs) can be used to identify the state of health of a fuel cell during operation. For perfluorinated sulfonic acid (PFSA)-based membranes, the degradation can be detected via its products such as fluoride or fluoride containing compounds [1]. These can then be monitored and detected through ex-situ effluent water measurements. There are multiple analysis methods available for analysing fluoride in water. The most prevalent ones in literature are ion chromatography (IC) or the use of a fluoride sensitive electrode (FSE). But there are also less commonly used methods like fluoride-19 nuclear magnetic resonance spectroscopy (19F NMR) or mass spectrometry (MS). Even new methods are being developed in the field, as we showed in our previous publication, where we introduced a photometric method for measuring fluoride emissions in water. It is based on the quenching of a zirconium complex, changing the transmission properties of the sample on a machine custom build by AiDEXA GmbH. The method can be used to measure small sample quantities of < 1 mL at only 60 s measurement time with a limit of detection (LOD) comparable to IC (Fig. 1) [2].
To test our method, we induced chemical membrane degradation in two samples, by employing an accelerated stress test (AST), based on a protocol developed by the DOE [3]. Chemical membrane degradation was monitored through capturing and analysing the effluent water in cold traps. Electrochemical characterisations were performed in addition to measure chemical degradation ex-situ and in-situ. We have not only shown our method to work fast and reliable, but also the chemical degradation happening in the cell, which was accelerated by increased cell temperatures. IC measurements also showed additional sulfate emissions, providing a more complete analysis.


Fig. 1: Calibration results of the AiDEXA photometric system in the range of 0 to 0.5 mg L−1. In (a), the transmission spectra are displayed as intensity vs. wavelength. In (b), the relation between standard fluoride concentration and the normed reference value features is shown [2].

REFERENCES
[1] M.A. Yandrasits, A. Komlev, K. Kalstabakken, M.J. Kurkowski, M.J. Lindell, J. Electrochem. Soc. 168 (2021) 024517.
[2] M. Heidinger, E. Kuhnert, K. Mayer, D. Sandu, V. Hacker, M. Bodner, Energies 2023, Vol. 16, Page 1957 16 (2023) 1957.
[3] N. Garland, T. Benjamin, J. Kopasz, ECS Trans. 11 (2019) 923–931.