Passive control of liquid water storage and distribution in a PEFC through flow-field design

Abstract

Liquid water stored in the diffusion media (DM) in a polymer electrolyte fuel cell (PEFC) can dramatically impact steady and transient performance, degradation, and heat transfer. In this study, seven different flow-field designs, with landing-to-channel (L:C) ratio from 1:3 to 2:1, were investigated at dry and fully humidified conditions, using neutron imaging. The results revealed the impact of flow-field geometry on stored liquid overhead is significant. In some cases, the stored water content in the cell can be nearly double that of another design, despite similar performances at low to medium current density. In general, a smaller L:C ratio reduces flooding losses and minimizes the stored water content. Additionally, the channel–DM interface plays a key role. For the same L:C ratio, a reduced number of channel–DM interfaces was shown to reduce flooding and stored liquid water content at steady state. This also suggests that using proper flow-field design can decrease the parasitic power consumption and the stored water content in the cell without any sacrifice from the cell performance. For dryer operating conditions, however, membrane dehydration becomes a dominant effect and a high landing-to-channel ratio flow-field is higher performing.