The gas diffusion layers (GDLs) play several important roles in polymer electrolyte fuel cells (PEFCs): conduction of heat and electrons, mechanical integrity and opposite-direction transport of gases and liquid water. This liquid product water is transported by capillary forces [1] throughout the GDL, forming tortuous pathways. State-of-the-art GDLs do not provide optimal characteristics for simultaneous water permeability and oxygen diffusivity. To address this issue, we are developing new GDLs with patterned wettability [2]. These materials provide low-resistance straightforward pathways for liquid water and dry low mass transport regions for the diffusion of gases [3].

In order to understand capillary transport in diffusion layers, Gostick et al. [4] developed an ex-situ experiment which allows obtaining saturation versus capillary pressure curves. This characteristic provides a very useful tool for designing optimized GDLs. We have used the same principle adapted for imaging (neutron radiography and X-ray tomography). In a recent publication [3], we demonstrated the capability of these materials to have water filled patterns at low capillary pressures (around 10 mbar), while significantly higher pressures (around 40-50 mbar) were needed to fill the hydrophobic regions (Figure 1).

In a more recent work, we have used two water injection strategies. The first consists in injection from a channel in the center of the GDL area and provides information about in-plane transport. The second brings the water equally distributed all over the area using a hydrophilic membrane [5], simulating a “cathodic” water transport situation, where water is produced all over the electrode.

In this presentation, we will show our latest results regarding parametric studies on differently treated GDLs. The effect of the following parameters on the capillary pressure characteristic has been investigated: type of carbon substrate (Toray, SGL and Freudenberg), coating load, hydrophilic monomer grafted (acrylic acid or n-vinylformamide), and width/separation of the patterns.

[1] U. Pasaogullari, et al., Int. J.Electrochem. Soc., 151(2004), 399.

[2] P. Boillat, et al., Patent Application EP14184065.2(2014).

[3] A. Forner-Cuenca, et al., Adv. Mater., 27, (2015), 6317.

[4] J. Gostick et al., J. Power Sources, 156(2006), 375.

[5] A. Lamibrac, et al., ECS 228^th Meeting Abstract (2015), MA2015-02 1539.

Figure captions:

Figure 1: Local water thickness measured with neutron radiography at different capillary pressures: 0, 10, 20, 40 and 50 mbar (top). Curves at different capillary pressures of water thickness and saturation as a function of the position is represented in the bottom graphic.