Characterization of Electrospun and Commercial Gas Diffusion Layers for PEMFC Using High-Resolution 3D Imaging and Direct Simulations
Résumé
This study presents an investigation into the microstructure and fluid transport properties of gas diffusion layers (GDL) in proton exchange membrane fuel cells (PEMFC) based on numerical characterizations and simulations of three-dimensional (3D) high-resolution images. Commercial GDLs (SGL 22BB, 22AA) and a microporous layer (MPL) from Sigracet are compared with an electrospun GDL. Synchrotron X-ray tomography and focused ion beam scanning electron microscopy (FIB-SEM) are employed for investigating the 3D structures with tailored resolutions. The study conducts a systematic validation of microstructural, monophasic, and biphasic transport properties against previous experimental and numerical results from the literature, demonstrating the robustness of the methodology. Yet, emphasis is placed on the crucial role of high-quality phase segmentation, performed here with a machine-learning approach, for defining mixed wettability. An objectively defined study volume is of first importance for commercial GDLs, possessing pronounced structural heterogeneities. The methodology is applied to an electrospun GDL featuring a pure and homogeneous carbon fiber substrate of submicrometer size, allowing for a unique comparative study in dry and water-saturated conditions. The impact of the microstructure on fluid transport properties is highlighted. Despite equivalent porosity, the presence of binder for the commercial GDLs leads to a 30% lower effective diffusion coefficient, but the small pore sizes of the eGDL lead to a reduced permeability of about 2 orders of magnitude. At equivalent saturation levels, water penetrates deeper into the eGDL structure without stagnation, leading to better preservation of fluid transport properties.