Coupled effects of flow field geometry and diffusion media material structure on evaporative water removal from polymer electrolyte fuel cells

In this work, the coupled effects of flow field geometry and diffusion media (DM) material structure on evaporative water removal during gas purge are investigated with the ex-situ test methods developed in previous works [31] and [32]. Three different flow field structures with various land to channel width ratios (L/C) were utilized with paper and cloth-type DM to understand the impact of L/C and DM properties on evaporative water removal rate, water distribution in DM, purge efficiency, and irreducible saturation. In the capillary flow dominant regime, it was determined that evaporative water removal is not significantly affected by L/C or DM properties, and can be semi-empirically correlated with critical purge time. The cloth-type DM was found to be superior to paper-type to mitigate the in-plane impedance of the land on water removal. In addition to the ex-situ evaporative tests, neutron radiography was utilized to visualize the in-situ water removal behavior. Results validate a novel purge protocol suggested by the authors in a previous study to achieve a more efficient and durable gas purge that preserves membrane durability.