The gas diffusion layer (GDL) is the key component for efficient mass and heat transport between the flow field structures and the catalyst layer of polymer electrolyte fuel cells (PEFC). The characterization of its transport properties under different compression levels is important to understand the implications of the inhomogeneous GDL compression on the channel-rib scale. While experimental and numerical studies show good agreement for GDLs with solid binder [1], the contributions of the porous binder in SGL type GDLs remain unclear [2, 3].

This work reports on the compression dependent characterization of the GDL morphology, mass and energy transport by means of X-ray tomographic microscopy (XTM) and numerical transport simulations of SGL 24 BA material. X-ray tomographic microscopy images were recorded with a 2.2 um voxel edge length. Though the pores in the binder are not resolved with such voxel dimensions, a specific segmentation procedure of the reconstructed images makes possible to distinguish between fibres, binder and void (see Figure 1, left). The porous binder domains are identified as stiff GDL component, as the volume of the binder domain remains constant for compression levels between 0 – 25 % (see Figure 1, right). In this compression range only the volume of the identified void domain reduces, the fibers deform but the binder domains are not affected. For compression levels above 25 % the binder starts to be compressed and the volume of the binder domains reduces similar as the overall GDL volume. Comparing numerical transport simulations with experimental GDL effective diffusivity and conductivity data, the binder effective transport parameters are determined for different compression levels.

References

[1] J. Becker, R. Flückiger, M. Reum, F. N. Büchi, F. Marone, M. Stampanoni, J. Electrochem. Soc., 156, B1175, 2009.

[2] R. Flückiger, S. A. Freunberger, D. Kramer , A. Wokaun, G. G. Scherer, F. N. Büchi, Electrochim. Acta 54, 551–559, 2008.

[3] A. Rashapov, J. T. Gostick, Transport in Porous Media, 115, 411-433, 2016.

Figure 1: Left) 3D rendering of a ternary segmented SGL 24BA gas diffusion layer at 0 % compression ; green: fibres, red: binder, white: void; Right) relative volume fractions of the components of the ternary segmentation as function of compression.