Z. Fishman

Microscale Tomography Investigations of Heterogeneous Porosity Distributions of PEMFC GDLs

A first comparison is made of the heterogeneous porosity distributions of various polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layer (GDL) materials. Microscale computed tomography imaging is performed for three main categories of commercially available GDL materials: carbon fiber paper, felt, and cloth. The methodology to analyze the through-plane and in-plane porosities of various materials is presented, and the relationship between heterogeneous porosity distributions and manufacturing techniques is discussed. This work also provides insight into the manufacturing process employed for GDLs.

Unstructured Pore Network Modeling with Heterogeneous PEMFC GDL Porosity Distributions

This is the first investigation of the liquid water saturation profile dependence on empirically determined heterogeneous polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layer (GDL) porosity distributions. An unstructured, two-dimensional pore network model using an invasion percolation algorithm is presented. Random fiber placements are based on the heterogeneous porosity distributions of six commercially available GDL materials recently obtained through X-ray-computed tomography visualizations. The pore space is characterized with a Voronoi diagram, and simulations are performed with a single inlet liquid water cluster. Saturation profiles are also computed for GDLs with uniform, sinusoidal, and square-wave porosity distributions. Liquid water tends to accumulate in regions of high porosity due to the associated lower capillary pressures. The results of this work suggest that GDLs tailored to have smooth porosity distributions have fewer pockets of high saturation levels within the bulk of the material. Finally, a study on theoretical surface modifications demonstrates that low porosity surface treatments at the catalyst layer|GDL interface result in greatly reduced overall saturation levels of the material.

Heterogeneous Through-Plane Distributions of Tortuosity, Effective Diffusivity, and Permeability for PEMFC GDLs

In this work, we applied the Tomadakis and Sotirchos transport model to heterogeneous porosity distributions measured from high resolution microscale computed tomography visualizations of polymer electrolyte membrane fuel cell (PEMFC) gas diffusion layers (GDLs). We calculated the corresponding local distributions of tortuosity ( T ), relative diffusivity [f(e)], and single phase permeability (K). The heterogeneous distributions of relative diffusivity and permeability strongly correspond to the measured heterogeneous porosity distributions, exhibiting transitional surface and core regions. Reasonable agreement was found between the average properties of the GDL core region with bulk values from literature. This work provides insight into the heterogeneity of important properties, which should be considered when modeling transport phenomena in the PEMFC GDL.