In-Plane Chemical Degradation Analysis of Polymer Electrolyte Membrane in Fuel Cells

Matsumoto, Ryuki

Predicting degradation of polymer electrolyte membrane fuel cells (PEMFCs) is an important issue from the viewpoint of durability and cost. In fact, in the roadmaps of each country, high targets of durability and performance are set for mobiles with Heavy Duty Vehicle (HDV) in mind. Among PEMFCs, polymer electrolyte membrane (PEM) plays an important role of proton conductivity and separating both poles. Therefore, if the mechanical strength is reduced due to the degradation of the PEM and it breaks, the function as a PEMFC is lost. For this reason, predicting degradation of PEM is an important issue in product design.

Various models have been proposed for the analysis of the chemical degradation of fuel cells. Most of these models are 1-D models focusing on the thickness direction [1]. However, the PEM is exposed to various conditions by in-plane distributions of gas flow, temperature and electrochemical reactions. For example, there is certain difference between conditions under flow paths and ribs. In-plane distribution under transient control of PEMFC is another important issue. Therefore, in this analysis, we investigate and report the in-plane distribution of chemical degradation behavior of PEM under various operating conditions.

The in-plane distribution such as the partial pressure of each gas and power generation required for the degradation analysis of the PEM in the in-plane direction is calculated using our in-house three-dimensional PEMFC simulation software, P-Stack [2]. P-Stack can estimate power generation performance in good agreement with experimental results, and can clarify relationships between the performance and internal states depending on cell designs, operating conditions, and material properties [2].

In this analysis, transient conditions of PEM is sampled from results of P-Stack simulations. Then, degradation behavior in various points in PEM is analyzed by the 1-D model, under those sampled transient boundary conditions. For the degradation model in the thickness direction, we refer to [1] and calculate a series of reactions of Nafion decomposition by hydroxyl radical (OH ). OH are generated from generated by two-electron oxygen reduction reaction mainly in anode catalyst layer. In this report, details of our modeling approach and approximation are explained. We will also discuss the relation between degradation behavior of PEM and internal states of PEMFC, depending on flow-field designs and transient operating conditions.

References

[1] Wong, K. H., Kjeang, E., J. Electrochem. Soc 161 (2014) F823

[2] T. Tsukamoto, T. Aoki, H. Kanesaka, T. Taniguchi, T. Takayama, H. Motegi, R. Takayama, S. Tanaka, K. Komiyama, M. Yoneda, J. Power Sources 488 (2021) 229412