With the current lack of understanding of the water transport phenomenon in the porous gas diffusion layers (GDLs) of the polymer electrolyte membrane fuel cells (PEMFCs), GDL designs are primarily implemented on a costly trial-and-error basis. In this work, an ex-situ device, suitable for micro-computed tomography (micro-CT) imaging, was designed to facilitate liquid water invasion of a GDL sample under flow field compression. The millimeter-scale apparatus allows for water injection from a

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... nt source with an opening diameter of 0.8 mm. A sample of felt-based Freudenberg GDL (H2315) was examined for the current study. Using micro-CT, the sample was scanned, before and after water invasion, to obtain high resolution, three-dimensional reconstructions of the dry GDL microstructures, as well as the liquid water patterns after breakthrough. These results were used to find the effect of liquid water content on the effective through-plane porosity for the felt-based Freudenberg GDL.