Effects of GDL wettability and water droplet size on the water removal from a PEMFC electrode by lattice Boltzmann method

Due to their important features such as low operating temperature, high power density, and ease of scale up, proton exchange membrane fuel cells (PEMFCs) expect a promising future. However, some technical barriers such as water flooding of electrodes exist in the path of their widespread commercialization. To mitigate water flooding, fundamental understanding of water droplet dynamic behavior in a PEMFC electrode is necessary. Generally, two mechanisms of inertial ejection and evaporation can be considered for water removal from the gas diffusion layer (GDL) of a PEMFC electrode. Inertial ejection mechanism (ejection of droplet to the channel by the inertial force of gas flow) is influenced by several parameters such as inertial, interfacial, viscous and gravitational forces and also GDL microstructure. On the other hand, evaporation mechanism is influenced by several parameters such as GDL thermal condition and wettability and also droplet size. All this said, water droplet removal from a PEMFC GDL is a complicated process which needs more fundamental research to be deeply understood. In the present study, the role of two effective parameters, GDL wettability (affecting both removal mechanism) and water droplet size (affecting evaporation mechanism), is investigated simultaneously by several 3D LB simulations. The results show that the inertial ejection mechanism may face with difficulties when GDL is not hydrophobic enough or the droplet size is not small enough.

Keywords:

multiphase flow , proton exchange membrane fuel cell , gas diffusion layer , wettability , water droplet dynamic behavior , lattice Boltzmann method