Modeling water transport at the interface between porous GDL and gas distributor of a PEM fuel cell cathode

Abstract

Operating vehicles with polymer electrolyte membrane (PEM) fuel cells is a promising technology for reducing traffic-related greenhouse gas emissions. In a PEM fuel cell, hydrogen and oxygen react producing water, electric energy, and heat. Oxygen is consumed on the cathode side of the cell, while the excess water must be removed to prevent the so-called flooding (blockage of the transport paths). A sophisticated water management is crucial for improved operating conditions of a PEM fuel cell. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents, where an intelligent use and drainage of the water buffer can be used to enhance the performance of the fuel cell. Pore-scale modeling of gas diffusion layers (GDLs) and the gas distributor has been established as a favorable technique to investigate the ongoing processes. A particular challenge is the investigation of the interface between the GDL and the gas distributor. Here, multi-phase flow in the porous material of the GDL is combined with the free flow in the gas distributor resulting in strong interaction. Different interface processes occur based on the pore-local structural properties, such as surface wettability and interaction with the gas flow in the gas distributor. At the interface between hydrophobic porous GDL and the hydrophilic side walls of the gas distributor, the fluids interact with the differently wetting surfaces. This results in complex pore-scale transport processes in the pores located at the interface. In the channels of the gas distributor, drops emerging from the porous domain at the interface have a strong influence on the exchange of mass, momentum, and energy between the two flow regimes. Additionally, we also consider transport processes of the gas phase between the GDL and the gas distributor, where no water breakthrough occurs.