Impact of MPL Thickness on Water Management of PEMFC by Synchrotron X-ray Radiography

The polymer electrolyte membrane fuel cell (PEMFC) is an efficient and clean energy conversion device. The performance of PEMFCs at high power operation is governed by product water management. The gas diffusion layer (GDL), a porous carbon fiber sheet, is sandwiched between a catalyst layer and a flow field, providing diffusive pathways for reactant gases and product water. A transient microporous layer (MPL) characterized by sub-micron size pores and hydrophobic contents applied on the GDL or catalyst layer is known to extend limiting current density. Past research [1] has shown that there exists an optimal thickness of MPL. However, the effect of varying MPL thickness has not been studied by visual inspection.

Our research group has successfully investigated liquid water dynamic and distribution in an operating PEMFC using synchrotron radiography [2-3]. For this study, a miniature fuel cell with an active area of 0.48cm²and 0.2mm channel and rib width was designed for improved image quality. MPLs of varying thickness (no MPL, 50μm, 100μm, and 150μm) were coated on TGP-H-60 (Toray Industries Inc.). Each fuel cell was operated according to a pre-determined testing scheme on a Scribner 850e fuel cell testing station (Scribner Inc.). Visualizations were performed at the Biomedical Imaging and Therapy Bending Magnet (05B1-1) beamline at Canadian Light Source Inc. (Saskatoon, Canada). Spatial and temporal resolutions were approximately 10μm and 0.3fps, respectively. Image processing was carried out according to the Beer-Lambert law. The processed image provides information on liquid water profile across components of the fuel cell (Figures 1 and 2). For each types of GDL, liquid water content at the interfaces and within microstructures will be analyzed to isolate effect of MPL thickness on water distribution and performance of the fuel cell.

References:

1. Jin Hyun Nam, Kyi-Jin Lee, Gi-Suk Hwang, Charn-Jung Kim, Massoud Kaviany, Int. J. Heat and Mass Transfer, 52, 2779-2791 (2009).

2. J. Lee, J. Hinebaugh, A. Bazylak, J. Power Source, 227, 123-130 (2013)

3. J. Hinebaugh, J. Lee, A. Bazylak, J. Electrochem. Society, 159 (12) F826-F830 (2012)