Investigating Inlet Condition Effects on PEMFC GDL Liquid Water Transport through Pore Network Modeling

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are promising electrochemical energy conversion devices due to their high efficiency, zero-local emissions, and rapid start-up capability. Water management is a vital issue in the PEMFC, as the accumulation of water directly affects its operating efficiency. During operation the membrane must be sufficiently humidified in order to achieve high proton conductivity; however, at high current densities, accumulation of liquid water in the cathode gas diffusion layer (GDL) blocks oxygen pathways, preventing this reactant from reaching the catalyst, which in turn hinders performance. Effective water management strategies are essential to improve PEMFC performance and require a detailed understanding of liquid water transport in the GDL.In a fuel cell stack, the cell components are assembled under compressive loads to prevent gas leakage; however, high compression of the GDL may affect cell performance. The non-uniform compression of the GDL, due to its contact with the bipolar plate, significantly alters the microstructure and consequently the dynamics of liquid water transport through the GDL [1]. A number of attempts have been made in experimental visualization of liquid water transport within compressed GDLs, but more work is required to evaluate these effects quantitatively [1-3].The purpose of this study is to numerically investigate the effects of compression on liquid water transport through PEMFC GDLs. In this work, two types of carbon paper GDLs are compressed. At each compression value, volumetric X-ray tomography images of the samples are obtained. The resulting greyscale images are segmented using a novel thresholding algorithm. A watershed algorithm [4] is used to extract pore networks of the GDL. Pore network modeling with invasion percolation is employed to determine the liquid water profile within the GDL over the range of compression states. The results of this study provide a deeper knowledge of how compression and the GDL microstructure affect the movement of liquid water.