(642a) The Importance of Polymer Electrolytes in Fuel Cell Electrodes in Meeting Performance and Durability Targets

This presentation will cover recent advances in the understanding of the impact of the polymer electrolyte binder (i.e., ionomer) on the performance and durability of polymer electrolyte fuel cells that are positioned to replace internal combustion engines in transportation applications, including medium and heavy-duty vehicles. Ionomer is critical for proton current conduction through the porous catalyst layers as well as providing an acidic environment at the catalyst interface. However, there is a recent consensus that there are several negative impacts of 5-10 nm thick ionomer coatings on platinum-based catalyst, including increased oxygen transport resistance and anionic poisoning of the catalyst by the ionomer’s acidic groups. The origin of the increased oxygen transport resistance due to the ionomer will be covered, including the effects of diffusion, solubility, and polymer chain rearrangement and densification at interfaces. The second part of the presentation will focus on recent advances in polymer electrolytes for the electrode, including alternatives to perfluorosulfonic acids (PFSA), multi-acid sidechains, short side chains, and ionomer modifications to prevent densification to increase oxygen transport. This last method of advancing ionomers is commonly referred to as high oxygen permeability ionomer (HOPI). Similarly, the use of tuned solubility to increase the apparent oxygen reduction reaction activity and increase efficiency will be discussed. The approaches for improving catalyst performance by displacing the Pt catalyst from the ionomer to reduce anionic poisoning will also be discussed. Finally, the impact that these polymer electrolyte advancements can have on durability will covered.