Water transport with different anisotropic fiber directions of the GDL

1 Water transport with different anisotropic fiber directions of the GDL 

The characteristics of the water removal from the GDL to the flow channel were investigated using the 25 cm active area cell. A comparison was made using photos of the growth of the liquid water film in the perpendicular cell and of a droplet in the parallel cell. The photos showed that water film flows from the side of the rib (land) to the channel with the perpendicular fiber direction. This shows that the accumulated liquid water inside the GDL under the ribs flows to the channels using the fiber direction perpendicular to the channel. However, with the parallel fiber direction there was a liquid droplet at the center of the channel and there was no apparent liquid flow from under the ribs. The behavior of the water indicates that the water may accumulate under the ribs when the fiber direction is parallel to the channels and that this accumulated water may affect the cell performance. 

An extensive ex situ study of the liquid water distribution in the anisotropic GDL was conducted with a cell freezing method. After the steady state operation was achieved, the cell operation was stopped and the cell assembly was cooled to below freezing temperature within 4 minutes. 

The accumulated water in the frozen state was then observed for the cross-sectional GDL. It was confirmed from the experiments that the ice distribution under the channels and ribs were very similar in the perpendicular case, while there was more ice under the ribs than that under the channels in the parallel case (Naing et aL, 2011). This suggests that the accumulated water can flow out more easily to the channels along the fiber direction in the perpendicular case. 

2 Water transport simulation in GDIs with different wettability gradients 

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