Modeling diffusion and convection in thin porous transport layers using a composite continuum-network model: Application to gas diffusion layers in polymer electrolyte fuel cells

Abstract

Mathematical modeling of porous media plays a key role to optimize the operation of electrochemical devices and guide the design of new materials. In this work, a composite continuum-network formulation is presented to model species diffusion and convection in gas diffusion layers (GDLs) used in polymer electrolyte fuel cells, which can be incorporated into CFD codes with moderate computational cost. The composite model includes a control volume (CV) mesh at the macroscopic scale, which embeds an internal microscopic pore network. Specifically, the pore network model is used to determine analytically the local anisotropic effective transport properties in the GDL (diffusivity and permeability), which are then mapped into the CV mesh to resolve macroscopic transport. Good agreement is found between the average structural parameters and global effective transport properties predicted by the model and previous data reported in the literature. Moreover, the results show important variations in the spatial distributions of the local properties due to microstructural heterogeneities, which significantly affect both bulk and interfacial fluxes in thin GDLs. Overall, the CFD model presented here provides an alternative approach for the analysis of porous materials in engineering applications, combining the ease of implementation of macroscopic continuum modeling and the computational power of pore network modeling.