X-ray computed tomography reconstruction and analysis of polymer electrolyte membrane fuel cell porous transport layers

A commercially available porous transport layer (SGL carbon group Sigracet® GDL 30BA), is investigated using X-ray computed tomography reconstruction. A novel aspect of this study is an investigation of the effects of non-homogeneous compression of the GDL 30BA sample including effective transport properties. Non-homogeneous compression is typical in polymer electrolyte fuel cells as the flow field plates consist of a series of lands and channels which apply an uneven loading to the porous transport layers. The X-ray computed tomography technique provides input data for the computer reconstruction procedures integrating image post-processing and iso-surface reconstruction. The resulting tomographic and surface reconstruction is converted into the computational volume/grid for microstructural and computational fluid dynamics (CFD) analysis. The heterogeneous compression effects on effective geometric and transport properties are investigated for various compression levels and effective transport properties are compared to theoretical studies such as Bruggeman [1] and Tomadakis and Sotirchos [2]. The effects of non-homogeneous compression are significant, with the transport properties differing by a factor of about 2 between the land and the channel regions. It is found that the effective transport properties are significantly lower than predicted by commonly used relations, with the lowest values representing only 15% of the predictions from the Bruggeman relation.