The Impact of Thermal Conductivity and Diffusion Rates on Water Vapor Transport through Gas Diffusion Layers

Water management in a hydrogen polymer electrolyte membrane (PEM) fuel cell is critical for performance. The impact of thermal conductivity and water vapor diffusion coefficients in a gas diffusion layer (GDL) has been studied by a mathematical model. The fraction of product water that is removed in the vapour phase through the GDL as a function of GDL properties and operating conditions has been calculated and discussed. Furthermore, the current model enables identification of conditions when condensation occurs in each GDL component and calculation of temperature gradient across the interface between different layers, providing insight into the overall mechanism of water transport in a given cell design. Water transport mode and condensation conditions in the GDL components depend on the combination of water vapor diffusion coefficients and thermal conductivities of the GDL components. Different types of GDL and water removal scenarios have been identified and related to experimentally-determined GDL properties.