Morphological Effects of Polytetrafluoroethylene Meniscus Formation on Microscopic Transport Properties of Inhomogeneous Random Porous Gas Diffusion Media for Electrochemical Applications

Abstract

In this study, the microscopic transport properties of porous gas diffusion media (PGDMs) with capillary meniscus formation are evaluated using a statistical approach for electrochemical applications. The microscopic morphology of PGDM is stochastically modeled using randomly distributed carbon fibers and various meniscus formations. In particular, the meniscus formation of hydrophobic polytetrafluorethylene (PTFE) agent enables the generation of highly elaborate microstructures in commercial PGDMs. A single-phase three-dimensional 19-velocity lattice Boltzmann method is applied to simulate the microscale mass transfer phenomena within the PGDMs. The mass transport characteristics (i.e., anisotropic permeability, tortuosity, and effective diffusion coefficient) of the PGDM samples with different PTFE content are statistically investigated as a function of untreated porosity (i.e., porosity before PTFE loading) of the PGDMs. The predicted results reveal an inverse relationship between anisotropic permeability and PTFE loading because the addition of PTFE decreases the bulk porosity of the PGDMs. In addition, the electrical and thermal conductivities of PGDMs are statistically estimated in both the in-plane and through-plane directions. The results show that the in-plane electrical and thermal conductivities are greater than those in the through-plane direction because of the carbon-fiber orientation. Moreover, the addition of PTFE has relatively larger effects on the through-plane electrical and thermal conductivities. [GRAPHICS] .