INVESTIGATING THE STRUCTURE OF THE BI-LAYERED GAS DIFFUSION LAYER USING X-RAY COMPUTED TOMOGRAPHY

摘要

One of the most important objectives of the GDL in a PEM fuel cell is the transport of reactant gases from the gas flow channels to the reaction sites at the catalyst layer. Most state-of-the-art GDLs are composed of a carbon fiber paper coated with a microporous layer composed of carbon nano-particles. This bi-layered GDL structure has been proven to provide significant improvement to the performance of PEM fuel cells. In order to improve our understanding of reactant transport through these GDL materials, it is important for us to characterize the structure of these materials. In this study, we use X-ray Computed Tomography (X-CT) to study the structure of the bi-layered GDL at the microscale. This work presents a unique segmentation routine developed in-house to identify the distinct components of the bi-layer GDL, isolating the carbon fiber, the microporous layer and the void regions as individual phases. Two commercially available GDL samples, SGL 35BA and SGL 35BC are segmented with this novel algorithm to obtain unique porosity profiles. The MPL is identified separately in SGL 35BC along with the fibrous substrate region. It is observed that in the case of this sample, there is no region where only the MPL is present. The entire thickness of the MPL region is within the substrate region with fibers present throughout the MPL region. The substrate region is 300 μm thick while the MPL is present up to 200 μm from one side.