Understanding the Mechanism of Chemical Durability Enhancement through Modeling of Electrolyte Membranes with Improved Oxygen Barriers

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In pursuit of a carbon-neutral society, polymer electrolyte fuel cells (PEFCs) are gaining significant attention in commercial applications, particularly for heavy-duty vehicles. The system demands long-term durability to its components, especially for polymer electrolyte membranes (PEMs), which require further thinning in the future[1]. The chemical degradation of PEMs occurs because of the attack by radical species. It is posited that hydrogen peroxide, arising from the crossover of oxygen, contributes to the formation of radical species. We hypothesized that introducing a gas barrier layer (GBL) against oxygen into the PEM could suppress chemical degradation, and confirming this hypothesis through durability tests using a GBL sandwiched between PEMs [2]. In this study, we constructed a model having the GBL to understand the mechanism behind this enhanced durability.According to the scanning electron microscopy (SEM) observations of the fabricated membrane electrode assembly (MEA) with the GBL (Fig. 1a), we constructed a 1D through-plane model of MEA (Fig. 1b). Species conservation equations were solved in each layer to calculate the potential and concentration. Reactions R1– R4 were assumed in the catalyst layers for the source terms of the conservation equations. 2H+ + 2e- → H2 (R1) O2 + 4H+ + 4e- → 2H2O(R2) O2 + 2H+ + 2e- → H2O2 (R3) H2O2 + 2H+ + 2e- → 2H2O(R4) We compared the distribution of hydrogen peroxide concentration in MEAs with and without the GBL by using our model. In MEAs with the GBL, a significant concentration (expressed by an equivalent partial pressure) gradient developed, leading to a reduction in oxygen concentration on the anode side (Fig. 2a) compared to those without the GBL (Fig. 2b). This indicates a lower oxygen flux towards the anode, which resulted in a reduced rate of hydrogen peroxide formation and lower concentrations in the MEA with the GBL. These results suggest that the presence of the GBL prevented degradation and enhanced the durability of the MEA. In the presentation, we will present the details of the model and discuss strategies for further enhancing the durability of MEAs with the GBL by showing various case studies. Figure 1