Identifying Water Thickness in Various Layers in PEMFCs through EIS and X-ray Radiography
In order to quantify the amount of liquid water in a PEMFC during operation, X-ray radiography was applied in the through-plane direction of the cell. Using the Beer-Lambert law, the processed images allowed for the liquid water to become visible in the anode and cathode flow channels, the anode and cathode gas diffusion layers (GDLs), the microporous layers (MPLs), as well as the membrane electrode assembly (MEA) . EIS was used as a non-invasive diagnostic tool in quantifying the equivalent resistances of the fuel cell. This study aims to quantify the water saturation of various layers of the fuel cell during EIS measurements, and demonstrate the role of the water saturation of each layer to the overall mass transport resistance of the fuel cell, measured through EIS. The fuel cells analyzed have varying MPL thicknesses, as well as fuel cells without MPLs, at increasing constant current densities. Nyquist plots will be discussed with relation to amount of liquid water visualized.
Figure 1. Subtracted in-plane image of the fuel cell with 150 μm-thick MPL. The image only shows 3 flow channels of 20.
Figure 2. Nyquist plot of the fuel cell observed simultaneously with x-ray radiography 1.0 A/cm2.
Figure 3. Water thickness profile plot at 1.0 A/cm2, from the image in Figure 1. Labeled from left to right: Anode GDL, Anode MPL, MEA, Cathode MPL and Cathode GDL.
 D. Malevich, E. Halliop, B. Peppley, J. Pharoah, and K. Karan, Journal of the Electrochemical Society 156 (2) B216 – B224 (2009)