Evaluating Defects Influence in Membrane Degradation Processes:a Performance-Durability Study Using Artificially Cracked Gas Diffusion Layers

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Although the degradation of the membrane electrode assembly (MEA) is a determining factor for performance and lifetime of proton exchange membrane fuel cells (PEMFCs), 1 it remains unclear how physical factors impact the MEA structure, especially the aspects related to the membrane. 2 Physical degradation of the membrane can be triggered by intrinsic factors such as membrane creep, microcracks, and morphological changes. 3 Membrane extrinsic factors such as roughness and imperfections at the interfaces between MEA components could disturb the membrane stability. Comparing the MEA components ––membrane, catalytic layer, and gas diffusion layer (GDL)–– in terms of thickness, roughness, and rigidity, the GDL mechanically supports the other MEA components, and GDL features could be the focal source of mechanical stressors in the MEA environment. To investigate whether structural features existing on GDLs can generate additional stress in the membrane, we designed a method to create artificial cracks on the microporous layers (MPLs) of commercial GDLs. Our methodology produces GDLs with a defined-controlled pattern of cracks (Cracked-GDLs) that––assembled to a catalyst-coated membrane (CCM), with uncracked catalyst layers–– ensures our network of cracks as the only external variable introduced into the MEA environment. The introduced pattern of cracks covers an area of (1.0 ± 0.1) % of the total surface of the GDL. Comparing results of cracked and pristine GDLs, we demonstrated that our 1.0 % of artificial cracks improves cell performance ––with an enhanced mass transport regio performance dominating the overall performance improvement. We also evaluated the mechanical and chemical durability of membranes using accelerated stress tests (ASTs) developed by the Million Mile Fuel Cell Truck (M2FCT) Consortium. The AST results show that the artificial cracks introduced on the GDL have no impact on the durability ––cracked and pristine systems failed after 500 hours–– and the improved performance generated by the cracks was preserved after durability test. Also, our pattern of cracks has a neutral effect in the catalytic degradation rate and in the current density changes at 0.7 V. Additionally, scanning electron microscopy (SEM) and laser profilometry were used to characterize all the samples, before and after performance/durability tests. Performance and durability results generated in this work give us insights to improve the membrane and GDLs technologies that we are developing under the M2FCT Consortium. Acknowledgement: This work was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortium, technology managers G. Kleen and D. Papageorgopoulos. References: (1) Liu, M.; Wang, C.; Zhang, J.; Wang, J.; Hou, Z.; Mao, Z. Diagnosis of membrane electrode assembly degradation with drive cycle test technique. International Journal of Hydrogen Energy 2014 , 39 (26), 14370-14375. (2) Qiu, D.; Peng, L.; Lai, X.; Ni, M.; Lehnert, W. Mechanical failure and mitigation strategies for the membrane in a proton exchange membrane fuel cell. Renewable and Sustainable Energy Reviews 2019 , 113 , 109289. (3) Borup, R.; Meyers, J.; Pivovar, B.; Kim, Y. S.; Mukundan, R.; Garland, N.; Myers, D.; Wilson, M.; Garzon, F.; Wood, D.; et al. Scientific Aspects of Polymer Electrolyte Fuel Cell Durability and Degradation. Chemical Reviews 2007 , 107 (10), 3904-3951.

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