Highly Permeable Perfluorinated Sulfonic Acid Ionomers for Improved Electrochemical Devices: Insights into Structure-Property Relationships

Abstract

<p>Rapid improvements in polymer-electrolyte fuel-cell (PEFC) performance have been driven by the development of commercially available ion-conducting polymers (ionomers) that are employed as membranes and catalyst binders in membrane-electrode assemblies. Commercially available ionomers are based on a perfluorinated chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low gas permeability and high mechanical strength but introduces significant mass-transport losses in the electrodes. These transport losses currently limit PEFC performance, especially for low Pt loadings. In this study, we present a novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel backbone chemistry induces structural changes in the ionomer, restricting ionomer domain swelling under hydration while disrupting matrix crystallinity. These structural changes slightly reduce proton conductivity while significantly improving gas permeability. The performance implications of this tradeoff are assessed, which reveal the potential for substantial performance improvement by incorporation of highly permeable ionomers as the functional catalyst binder. These results underscore the significance of tailoring material chemistry to specific device requirements, where ionomer chemistry should be rationally designed to match the local transport requirements of the device architecture.</p>

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

“…153 Katzenberg et al showed that inserting a small ring into the ionomer backbone structure significantly improved its gas permeability because the modified ionomer restricted the expansion of the ionomer domain in the hydrated state while disrupting the matrix crystallinity. 176 2.4.3.2. Carbon Support.…”

Advancements in cathode catalyst and cathode layer design for proton exchange membrane fuel cells

“…They showed that a denser, water-depleting ionomer layer of 3 nm lies on top of the metal particles and leads to an activation barrier for oxygen diffusion from the gas phase to the active site. To minimize this diffusion barrier effect, Modestino and coworkers created a new group of porous, proton-conducting ionomers based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone structure enabling high oxygen permeability 64 . With a different approach, Yoshino et al presented an electrospinning method manufacturing CL with ionomer nanofibers 65 .…”

Investigation of Hydrogen Oxidation and Evolution Reactions at Porous Pt/C Electrodes in Nafion-Based Membrane Electrode Assemblies Using Impedance Spectroscopy and Distribution of Relaxation Times Analysis

“…79 Minimization of this resistance could be achieved through the use of a thinner membrane at the cost of higher gas crossover, or by the use of alternative membrane designs that improve the hydrophilicity or ion exchange capacity. 82 An improvement in the ionic conductivity of the membrane of 2x is sufficient to decrease the cell impedance by 40% at room temperature.…”