| Résumé | High throughput and product quality are essential for the scalable production of cost-effective polymer electrolyte membrane fuel cells (PEMFCs). Therefore, it is important to understand the possible implications of various material defects that could appear in the manufacturing process. During the fabrication and assembly of catalyst-coated membranes (CCM)s, the catalyst layers (CL)s may contain void regions of partially missing material due to deficient deposition or unintentional removal, which could affect fuel cell performance and durability. For instance, CL cracks have been shown to expand and propagate into more harmful membrane cracks. In addition, local thickness differences in CCMs arising from missing CL sections or deficiencies in other components could result in local stress concentration and susceptibility of membrane pinhole formation. Therefore, in general, a missing section of the CL area or other similar irregular features in the CL of a CCM may imply categorizing these CCMs as defective (i.e., scrap) and excluding them for fuel cell assembly. However, on the contrary, M. Kim et al. found increased cell performance for cracked CCM via tensile forces (within the elastic strain region) due to improved mass transport and decreased membrane resistance.
Consequently, to improve the understanding of CCM defects, the present work investigates how different missing cathode catalyst layer (CCL) areas affect the PEMFC performance and durability. In more detail, we prepared via ultrasonic spray coating 25 cm² active area MEAs with 4.0, 5.9, and 8.5% missing CCL areas obtained by masking (as shown in the Figure), and compared these to defect-free CCL baselines.
The results of this study feature a comprehensive assessment of the fuel cell performance of the defective MEAs compared to the baseline MEAs. This includes extraction of the membrane and charge transfer resistances from the missing CCL areas via medium- and high-frequency equivalent circuit modeling of in-situ electrochemical impedance spectroscopy (EIS) data at a current density of 0.1 A/cm² and contact, membrane, charge transfer, and mass transfer resistances at a current density of 1 A/cm². Findings on the influences on the electrochemical surface area, hydrogen cross-over current density, and double-layer capacitance from such missing CCL area will also be presented. Results from chemical/mechanical and electrochemical cycling tests will also be shown regarding the effect on durability from the missing CCL area.
The results from this work may benefit the economy of scale for high-volume fuel cell manufacturing by reducing unnecessary CCM replacements and materials waste by providing a threshold for an acceptable missing CCL area. |
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