Highly Durable Fluorinated High Oxygen Permeability Ionomers for Proton Exchange Membrane Fuel Cells

For proton exchange membrane fuel cells to be cost-competitive in light- and heavy-duty vehicle applications, their Pt content in the catalyst layers needs to be lowered. However, lowering the Pt content results in voltage losses due to high local oxygen transport resistances at the ionomer-Pt interface. It is therefore crucial to use ionomers that have higher oxygen permeability than Nafion. In this work, novel high oxygen permeability ionomers (HOPIs) are presented, with up to five times higher oxygen permeability than Nafion, synthesized by copolymerization of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) with perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE). PDD is the source of higher permeability due to its open ring structure, while PFSVE provides ionic conductivity. Optimization of PDD content and equivalent weight enables increased fuel cell performance, mainly at high current densities, where HOPIs can achieve power densities >1.25 W cm(-2) and exceed the 0.8 A cm(-2) U.S. Department of Energy durability target by losing only 4.5 mV, which is over six times less than 30 mV. The interactions between HOPI and SO3- groups with a PtCo/C catalyst are also elucidated here at a fundamental level.

Automated summary

In order to make proton exchange membrane fuel cells cost-competitive in vehicle applications, the Pt content in the catalyst layers needs to be reduced. This paper presents novel ionomers with significantly higher oxygen permeability than traditional materials. By optimizing the composition and quality of the materials, fuel cell performance is improved and can exceed the durability targets set by the U.S. Department of Energy.