Effect of material properties on evaporative water removal from polymer electrolyte fuel cell diffusion media

This work is devoted to delineating the fundamentals of evaporative water removal from diffusion media (DM) to achieve highly efficient and durable gas purge. Multiphase water transport from DM during gas purge is characterized by a balance of internal capillary liquid water flow and water vapor diffusion. In this study, DM with polytetrafluoroethylene (PTFE) content ranging from 0 to 20 wt%, and DM with three different geometric pore structures are utilized to understand this material property effect. It is found that overall evaporative water removal rate increases as PTFE content decreases and as the geometric pore structure changes from a two- to a more three-dimensional structure. This is due to the increase of wettability and porous space favorable for the water transport. The effect of phase-change-induced (PCI) flow and capillary flow on water removal is compared, and it is found that PCI flow is dominant at lower saturation of DM, whereas capillary flow is dominant at higher saturation. The results of this study build upon a previous study by the authors (Cho and Mench [17]), and are useful to understand the competing phenomena of water removal in PEFC DM. The ultimate goal of this work is to guide material design to achieve purge that preserves membrane durability with reduced shutdown power requirements.