Spatiotemporal Behavior and Two-Phase Transport in Porous Electrodes of PEM Fuel Cells

Significant barriers that need to be resolved before proton exchange membrane (PEM) fuel cells may be commercialized are related to the electrode performance and the water management in electrodes. Recent experimental evidence1,2 and theoretical analysis3,4 suggest that water management is strongly influenced by transport phenomena at the interface between the electrode components. Phenomena such as the “eruptive water ejection”1,2 at the cathode gas diffusion layer (GDL)- channel interface, or the saturation discontinuity between adjacent electrode layers are driven by capillarity and ultimately control the amount of water residing in the fuel cell components.

The goal of this study is to analyze numerically the effect of the interfacial phenomena on the spatiotemporal behavior and the two-phase transport in PEM fuel cell cathode electrodes using three-dimensional, multiphase, multi-fluid computational fluid dynamics. The numerical analysis shows that the water dynamics in the electrode are strongly time-dependent, exhibiting rearrangements of streamlines and saturations as liquid water builds up in the diffusion media. Further, the liquid water streamlines and the local saturation inside the diffusion media change in time, depending strongly on the location and stage of formation of the pendant or sessile droplets which form, grow and detach at the cathode GDL – channel interface. We analyze diffusion media structural properties that affect the amount and the dynamics of the liquid water that resides in the electrode during operation. We also analyze parallel mechanisms of water transfer between catalyst layer pores and the ionomer during fuel cell operation.