A phase-dependent constitutive model to predict cyclic electrical conductivity in fuel cell gas diffusion media

Structure-property relation in fuel cell gas diffusion layer (GDL) is a dependent function of its constituents. The bulk electrical conductivity of these layers is known to be relative density function varying due to external force or cell operating conditions. To locally predict the changes due to complex working conditions, an accurate model that predicts the nonlinearity of GDLs is highly desirable. To this end, this article proposes a material model that is phenomenologically derived to address the cyclic electrical conductivity of GDLs. Functional variables are taken to operate on porosity variation, fiber contact density, and fiber dislocation parameters. In the presence of these parameters, the results illustrate nonlinear conductivity variation with the magnitude of applied cyclic compressive load. Through successive loading-unloading, the porous structure is modeled to reach a steady-state reflecting stable conductivity-stress behavior for the constant stress limit. An interesting behavior of GDL can be captured where conductivity reduces as compressive load exceeds a threshold limit called break stress due to fiber breakages or dislocations. A greater applicability of this model may lie in mapping localized in-situ response of GDLs under cyclic operations.

Automated summary

This article proposes a material model to predict the nonlinearity of fuel cell gas diffusion layer (GDL) conductivity, taking into account functional variables such as porosity variation, fiber contact density, and fiber dislocation parameters. The results show that the GDL conductivity varies nonlinearly with the magnitude of applied cyclic compressive load, and there is a decrease in conductivity when the compressive load exceeds a certain threshold.