The electrolyte-catalyst interface in the cathodes of polymer electrolyte fuel cells (PEFCs) has a significant impact on the utilization, performance, and durability of fuel cell systems. The ionomer plays a critical role in providing a facile proton conduction pathway from the membrane to the Pt-based catalyst and creating an acidic local environment for the oxygen reduction reaction with high specific activity. However, the commonly used perfluorosulfonic acid (PFSAs) ionomers also negatively impact performance by hindering oxygen transport and partial poisoning of the catalyst by the anionic acid groups. There is a growing consensus that the densification of the PFSA ionomers at the Pt-alloy catalyst greatly increases the local oxygen transport resistance relative to permeation through bulk PFSA films. To address this issue, new high oxygen permeability ionomers (HOPIs) that resist the densification are being developed. This presentation will present our development of membrane electrode assemblies (MEAs) with HOPI in the cathode. The results include a model-based analysis, ink and coating optimization, and experimental fuel cell and transport characterization. The results highlight the significant increase in voltage efficiency and maximum power density when fabricating cathodes with HOPI as well as the significant positive impact on performance durability.This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.