Non-active area water mitigation in PEM fuel cells via bipolar plate surface energy modification

Abstract

The management of liquid water from either internal chemical reactions or externally humidified reactants is an important design consideration for proton exchange membrane (PEM) fuel cells because of the effects on both cell performance and durability. To achieve proper water management, significant effort has been devoted to developing new fuel cell materials, hardware designs, and appropriate stack operating conditions. However, water management in the region of the channel-to-manifold interfaces has received limited attention. This region covers the ends of the bipolar plate from where liquid water exits the active area to the entrance of the stack exhaust manifolds where excess reactant flows from individual cells are combined and leave the stack. For practical applications, there is a small driving force to expel liquid water in this region, especially in the anode flow field. Under severe operating conditions such as freezing temperatures, the buildup of water may cause a channel-scale blockage. In this study, hydrophilic and hydrophobic bipolar plate treatments were investigated to identify the effectiveness of water mitigation through ex-situ experiments performed using a dedicated freeze test rig. Water mitigation behavior with various locations of hydrophilic/hydrophobic coatings was characterized using measurements of differential pressure and gas flow rate. It was found that the hydrophilic coatings provide better performance, as water accumulation can be readily mitigated with less potential to cause full channel-scale blockages.