Porous Carbon Fiber Flow Fields for Heavy-Duty Polymer Electrolyte Fuel Cell (PEFC) Applications

Abstract

The US Department of Energy (DOE) interim (2030) targets for polymer electrolyte fuel cells (PEFCs) in heavy duty vehicle applications accentuate reduced system cost (US $80/kW), increased peak efficiency (68%), and longer system lifetime (25,000 hrs) [1]. The bipolar plate in a PEFC has to serve several functions such as uniform reactant distribution with minimum pressure loss, efficient product water removal, and maintain high electronic and thermal conductivity. Multiple studies [e.g., 2-4] describe novel materials and engineered designs potentially meet these performance and durability requirements; however, cost is the limiting factor in most cases. For example, the cost of a state-of-the art stainless steel (SS 316L) plate, already approaching minimum feasible plate thickness, is estimated to be (US $3.5/kWnet), which is 17% higher than current DOE target [1]. Thus, low-cost substrate alternatives are required to reduce the cost and facilitate commercialization in heavy-duty applications. One such alternative is a novel PEFC architecture [5] utilizing a laminated structure consisting of flat thin metal foils that separate flow fields with channels formed into the porous gas diffusion layer (GDL). This architecture enables the use of much thinner metal plates compared to stamped ones, reducing the overall system mass and cost. The current study explores the performance of a wide aspect ratio (200 mm x 30 mm) PEFC test fixture with porous carbon fiber flow field compared to conventional solid flow field over a wide range of operating conditions. The wide aspect ratio and channel/rib dimensions for both the porous and the conventional solid flow field are chosen to provide a reasonable pressure loss relevant to heavy-duty PEFC stack application. This new architecture is expected to enable comparable system performance while reducing plate weight and cost.