The 3D microstructure of the gas diffusion layers (GDLs) is generated, using a stochastic reconstruction approach. The method uses basic input parameters and fibers orientation distribution and is capable to model carbon fiber and binder phases of all types of carbon fiber GDLs with different structural parameters. Morphological operators of image processing are used to add the binder to the fibrous skeleton in three dimensions. Binder impregnation, pore size distribution and tortuosity factor of the reconstructed GDL are evaluated and compared with literature. Twenty and forty percentages of binder volume fraction are used to reconstruct the microstructure. To further investigate the reliability of our approach, mass transport properties of the reconstructed microstructure, namely absolute permeability, effective diffusivity of the pore space and effective thermal conductivity, are investigated through a finite volume equation solver in AVIZO. Only 4% of discrepancy between the absolute permeability calculation and the value reported by the manufacturer is observed in the through‐plane direction. Finally, in order to show the flexibility of the methodology the microstructure of a commercial Toray GDL is also reconstructed and characterized. The proposed method is proved to be a high‐speed and versatile tool for research and development in the GDL material design.
Mass transport and conductivity properties of the carbon fiber papers (CFPs) used in gas diffusion layers are among the critical parameters that affect a proton exchange membrane fuel cell (PEMFC) performance. Here, instead of carbonization/graphitization in the commercial CFPs manufacturing steps, the expanded graphite (EG) is numerically added to the CFP substrate to compensate and enhance the conductivity. The microstructures of different polymer binder/carbon fiber (CF) composites with and without EG are reconstructed using a digital 3D reconstruction technique. The binder phase is discriminated as an individual phase using image processing, and the effects of different binder percentages are demonstrated. In comparing the properties, the reconstructed CFP exhibited satisfactory properties against the values of the commercial CFPs in the literature and our conducted experimental tests. For the binder/CF/EG CFPs, 1.9 W/mK of effective thermal conductivity in the through-plane direction and also 30.2 m .cm of the in-plane electrical resistivity are reached, compared to 0.48-1.8 W/mK (for Sigracet and Toray papers) and 12.9 m .cm (for untreated Toray TGP-H-60), in the conventional CFPs. Overall, adding EG to the CFPs substrate provides valuable properties and can be considered as a proper replacement in future design and manufacturing of CFPs.
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