Investigating the Water Transport in Porous Media for PEMFCs by Liquid Water Visualization in ESEM

A novel ex situ method of investigating the water transport in porous media for PEM fuel cells with an environmental scanning electron microscope (ESEM) is introduced. By applying two different experimental methods, a liquid water pressure gradient is created which is necessary for the liquid water transport in porous media. The first method relies on water condensation on the bottom surface of the GDL to introduce a liquid phase into the porous media. The second method applies an external pressure gradient. The relevance of the methods is shown by visualizing the water formation and transport in different GDL materials with the high spatial resolution of an ESEM. In all experiments, the fingering effect, proposed by other researchers could be confirmed. However, the water formation on the surface of the GDLs is not consistent with the common idea of water formation in GDLs. The methods were also used to investigate the advantageous effect of laser perforating GDLs on fuel cell performance. The water transport visualization near a hole of a laser perforated GDL supports the assumptions of lower liquid water saturation in the GDL (due to effective water transport in the channels), and larger in-plane water transport towards the perforations.