Chapter 8 - Modeling the Gas Diffusion Layers

Abstract

This chapter describes the theory and commonly used equations for modeling the fuel cell gas diffusion layer (GDL). The gas diffusion layer is between the catalyst layer and the bipolar plates. The catalyst, gas diffusion, and membrane layers are sandwiched between the flow field plates in a polymer electrolyte membrane (PEM) fuel cell. Physical description of the GDL, basics and modes of transport of modeling porous media, and types of models are discussed. GDLs provide electrical contact between electrodes and the bipolar plates and distribute reactants to the catalyst layers. They also allow reaction product water to exit the electrode surface and permit the passage of water between the electrodes and the flow channels. A GDL must be a good proton conductor, chemically stable, and able to withstand the temperatures and compression forces of the fuel cell stack. Common methods used to model porous media include modeling the gas and fluid through the pores and modeling the interaction of the gas/fluid with the solid porous media. Commonly used methods for modeling the GDL include Fick's law, Darcy's law, and the Stefan–Maxwell diffusion for the mass transport. Ohm's law is typically used for charge transport, and energy balances can be made on the system in order to obtain the most accurate flow rates, velocities, and pressure drops through the porous media layer.