Invited: Remaining Technical Challenges in R&D for Automotive PEM Fuel Cell System

Abstract

It is a consensus that the cost and durability of the hydrogen PEM fuel cell system are still significant challenges to overcome before fuel cell vehicles can compete in the market [1]. The US Department of Energy (DOE) sponsored fuel cell cost study estimates the 2012 cost of automotive fuel cell systems to be $51/kW, assuming high volume production [2]. This is more expensive than the DOE target of $40/kW even though the study uses an aggressively low platinum group metal (PGM) catalyst loading assumption. This means that a reduction of PGM loading by itself may not be sufficient. The USDRIVE Fuel Cell Tech Team Roadmap indicates that increasing the area specific power density is the most effective way to reduce cost, followed by reduction of platinum (Pt) loading in the fuel cell stack [1]. To find technical solutions, it is necessary to pursue not only engineering to develop incremental improvements, but also fundamental research to improve baseline performance. The remaining fundamental research can be focused on two areas: mass transport overpotential and catalyst mass activity. It is also important to obtain these technical solutions while providing for a durable system.The oxygen reduction reaction (ORR) overpotential at the cathode is significantly greater than the overpotential of the hydrogen oxidation reaction [3, 4]. Therefore, the oxygen concentration in the cathode is vital for the performance and operational robustness. Particularly, providing high oxygen concentration at high current density operation is critically important to enhance the area specific power density. However oxygen concentration at the cathode is locally lowered by unsatisfactory water management [5-7]. Thus, mass transport overpotential at high current density is the major barrier to achieving high power density with acceptable operational robustness. Experimental investigation of mass transport has been limited by an inability to resolve water saturation-dependent properties in the gas diffusion layer. An approach of computational fluid dynamics based Thermal Lattice Boltzmann Method has been taken to represent gas/liquid transport in the cathode [8]. Ford is working with the University of South Carolina in this area. A risk of this approach is the accuracy of the mathematical modeling which will provide direction for the advanced mass transport design. To mitigate it, ex-situ material characteristics and in-situ data will be pursued to validate the modeling. A novel analytical methodology has been developed to measure oxygen partial pressure in the flow field by using oxygen sensitive fluorophore molecules [9].Enhancing the catalyst mass activity for ORR is also imperative to achieve the cost target. The most important need in catalyst research is to improve performance and durability at the same time under automotive usage conditions. One of the approaches of catalyst development looks at morphology of catalyst and its support materials. A newly developed Pt two dimensional nanometer scale network structure on amorphous niobium oxide support shows high mass activity and durability at the same time [10].The technical outlook and research approaches for remaining technical challenges of automotive PEMFCs will be discussed at the ECS meeting.