Microscale Investigation of the Transport Characteristics in Surface-Treated Gas Diffusion Layers with Gradient Porosities for Fuel Cell Applications

Abstract

In the present study, microscale transport phenomena in gas diffusion layers (GDLs) with gradient porosities are investigated statistically. A series of GDLs are randomly generated with linear and nonlinear gradient porosities at a 95% confidence level to reflect the heterogeneous microstructures. Straight-cylindrical carbon fibers with a uniform diameter are randomly arranged layer-by-layer and then treated with various polytetrafluoroethylene (PTFE) loadings. Furthermore, the reactant transport phenomena throughout the GDLs are simulated using lattice Boltzmann method (LBM). Then, the corresponding mass transport characteristics (i.e., permeability, tortuosity, and effective diffusion coefficient) are predicted in a series of GDL samples. The predicted data reveal an inverse relationship between permeability and PTFE loading. Moreover, the results show that GDLs with gradient porosities are more favourable to the reactant gas diffusion, leading to larger permeability than those of GDLs with uniform porosities. Besides, electrical and thermal conductivities of GDLs are computed in both in-plane and through-plane directions, and show good agreement with published experimental data. These statistical results show that the microscopic transport characteristics of PTFE-treated GDLs with gradient porosities are strongly affected by porosity distribution and PTFE loading. The proposed model can be utilized to optimize GDL structures and investigate the effect of PTFE on microscale transport characteristics of GDLs.