Quantitative MRI study of water distribution during operation of a PEM fuel cell using Teflon® flow fields

Water management remains a leading challenge in the implementation of small polymer electrolyte membrane (PEM) fuel cells for portable electronic applications. At present there are many excellent models for the distribution of water within PEM fuel cells, but little quantitative data on the water distribution that can be compared to models. In this paper magnetic resonance imaging (MRI) is used to examine the water distribution in the flow fields of an operating PEM fuel cell. While previous workers have used MRI to do qualitative measurements of the water distribution, we use MRI to quantitatively measure the water distribution for the first time. We find that even with Teflon® flow fields the GDL is so hydrophobic, that water is drawn away from the cathode GDL and accumulates at the bottom of the flow field. The flow pattern in the flow field seems to be wavy-stratified flow rather than plug flow as previously supposed. Additionally, we find that water is transported from the cathode to the anode. Thus, diffusional forces and hydrophobic capillary pressures appeared to dominate electroosmotic forces, at low current densities.