Transient characteristics of in-plane water transport in gas diffusion layers of PEM fuel cells

Abstract

During the operation of proton exchange membrane (PEM) fuel cells, water and heat are produced as two byproducts. A reliable and continuous operation of a PEM fuel cell requires an efficient water removal from the porous structure of the electrodes. In PEM fuel cells, gas diffusion layers (GDL) are used to effectively remove the produced water from the electrodes and also to supply reactant gases across them. The focus of this study is to characterize liquid water percolation within the plane of the GDL by utilizing a nondimensional energy ratio-time scale model (Ce-t∗). The transport phenomena are investigated for various GDL compressions, GDL samples with the microporous layer (MPL), and a degraded GDL sample. The transition between flow regimes is characterized based on the variation of slopes in Ce-t∗ curves. The flow regimes were observed to change from fingering and channeling in the capillary fingering regime to macro-transport along with uniform percolation in the stable displacement regime. It was observed that GDL compression can expedite flow regime transition and can cause faster energy dissipation during steady state periods. When MPLs were added to the GDL, the wetted areas were observed to occur at more dispersed locations. Finally, the experiment conducted with a degraded GDL without an MPL demonstrated higher slopes in the Ce-t∗ curve, indicating more frequent liquid water flooding. This could ultimately result in reduced cell performance.