Water breakthrough behavior and GDL degradation mechanisms in a PEM fuel cell

The water that exists within the porous components of a proton exchange membrane fuel cell (PEMFC) during operation affects the performance characteristics of the fuel cell. The water transport processes through the gas diffusion layer (GDL) and microporous layer (MPL) are suspected to change over the cell lifetime due to material degradation mechanisms. The understanding of how GDL degradation affects its water transport mechanisms is needed so that GDL and MPL material can be optimized for maximum PEMFC performance and durability. One of these water transport mechanisms is capillary action. Measuring the capillary breakthrough pressure (CBP) is a novel characterization method where water is delivered to an initially dry GDL sample at a low flow rate. Studying the dynamic capillary pressure (DCP) can add insight to how the water is emerging out of the GDL. Various ex situ experiments have been conducted involving the study of the water breakthrough dynamics inherent to different GDLs. However, these experiments have only been performed on fresh GDLs. A novel ex situ test section was designed to not only degrade GDLs but also to measure the CBP before and after the degradation process. The GDLs were degraded by being exposed to simulated conditions seen at the cathode side of a PEMFC. These conditions included electric current, temperature, compression, and accelerated liquid water flow and were applied to the samples for prolonged periods of time. Degradation mechanisms were identified through the use of CBP measurement and DCP observation, surface wettability measurement, confocal laser scanning microscopy, and compositional analysis on the GDL samples before and after degradation