Study of Flooding and Drying Effects in an Industrial-Size PEMFC Using Locally Resolved Impedance Spectroscopy

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Achieving the target lifespan remains one of the most important challenges in the commercialization of low-temperature proton exchange membrane fuel cells (LT-PEMFCs) for heavy-duty applications. A key factor limiting the durability is the lack of effective water management. While flooding is normally reversible, excess liquid water in the anode can lead to localized hydrogen starvation, which results in carbon corrosion and irreversible performance losses [1]. Membrane dehydration must be avoided too, as it can cause mechanical stress and pinhole formation, increasing the ohmic resistance and hydrogen crossover[2,3]. Several methodologies are employed to study flooding and drying phenomena in PEMFC, including voltage monitoring, EIS, pressure drop, etc[4,5]. EIS is widely used to detect HFR and mass transport resistance variations over time [5]. The measurements represent an average across the entire active area. Therefore, in large-scale systems, localized diagnostics are highly desirable, particularly at the inlet and outlet regions, as they provide a more precise evaluation of how operating conditions affect the performance[6]. This study presents a novel approach to water management diagnostics through localized voltage and EIS measurements. To detect potential flooding or drying, parameter variation tests were conducted, in which extreme conditions were evaluated. The spatially resolved measurements were performed with a segmented bipolar plate (>300 cm 2 ), which contains segments of 16 cm 2 each at the top and bottom of the cathode inlet and outlet areas. These measurements were then compared with conventional measurements averaged over the whole active area. Our localized methodology revealed critical spatial variations. For instance, reducing the oxygen stoichiometry led to a significant voltage drop at the cathode outlet areas, while the inlets remained unaffected. This effect is not visible when measuring the entire active area of the cell. Similar trends were observed when varying relative humidity, temperature, and pressure. Localized EIS showed remarkable increases in mass transport resistance at the cathode outlet areas when very wet conditions were tested (e.g., low pressure, high humidity), while the inlet segments remained almost unchanged. On the other hand, HFR measurements revealed that the cathode inlet was highly sensitive to dry conditions, showing strong fluctuations, whereas the outlet areas remained stable under the same conditions. The insights of this study have shown the critical importance of spatially resolved diagnostics to optimize the operation strategy of our industrial-size PEMFC. The implementation of localized EIS has many other potential applications; it can be used in future works to obtain deeper insights into the effects of accelerated stress tests, overall improvements in state-of-health diagnostics and a precise end-of-life analysis. References [1] J. St-Pierre, D. Wilkinsor, S. Knights, M. Bos, Relationships between water management, contamination, and lifetime degradation in PEMFC, J. N. Mater. Electrochem. Syst. 3 (2) (2000) 99–106. [2] F. A. de Bruijn, V. Dam, G. Janssen, Durability and degradation issues of PEM fuel cell components, Fuel Cells 8 (1) (2008) 3–22. [3] M. Schoemaker, U. Misz, P. Beckhaus, A. Heinzel, Evaluation of hydrogen crossover through fuel cell membranes, Fuel Cells 14 (3) (2014) 412–415 [4] Wang, X. R., et al., Review on water management methods for proton exchange membrane fuel cells, International Journal of Hydrogen Energy 46.22 (2021): 12206-12229. [5] F. Mack, R. Laukenmann, S. Galbiati, J.A. Kerres, R. Zeis, Electrochemical impedance spectroscopy as a diagnostic tool for high temperature PEM fuel cells, ECS Trans . 69 (17) (2015) 1075. [6] Trogisch, Niklas, et al. "Temporary high temperature operation of an automotive PEM fuel cell: Analysis of local degradation mechanisms." Journal of Power Sources 647 (2025): 237310. Figure 1

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