(146f) Micro Computed Tomography Investigation of Water Distribution and Transport in a Gas Diffusion Media

Proper water management has long been identified in the literature as a key component for optimal fuel cell performance. Current literature suggests that the lack of in-situ water data is slowing the progress of water management technology. Water motion in an operating polymer electrolyte membrane (PEM) fuel cell has been examined with Micro computed tomography (CT) in our previous research. In this work, Micro CT was used to look through the gas diffusion layer (GDL) to provide accurate two-dimensional (2D) and three-dimensional (3D) pictures of water inside two types of carbon paper, both plain and standard wet proof.

The results demonstrated many details of the water motion in the GDL. 2D pictures showed that water was diffused perpendicularly to the GDL surface. However, once water entered the carbon paper, it diffused parallel to the surface as well. The diffuse rate in the plain carbon paper was much quicker than the diffuse rate in the wet proof treated carbon paper. 3D images further confirmed recent numerical and experiment studies of the co-existence of hydrophilic and hydrophobic areas of the GDL. Although previous numerical studies demonstrated that the more hydrophilic the GDL was, the more water accumulated inside, our 3D images indicated deviations from those results. We found less water distribution on the surface of the more hydrophobic carbon paper, however, inside the carbon paper, the water distribution was almost the same as the plain carbon paper. A potentiostatic test was also conducted in order to find the relationship between characteristics of the GDL and of PEM fuel cell performance. Better fuel cell performance was observed with the carbon paper with standard wet proof. This was believed to be due to the different water distribution pattern inside these two types of carbon paper, which caused different mass transfer barriers.