Radiation Grafted Ion-Conducting Membranes: The Influence of Variations in Base Film Nanostructure

Abstract

The proton exchange membrane (PEM) is a key element of a polymer electrolyte fuel cell, and radiation-grafting is an attractive option for the synthesis of PEMs. Via a systematic investigation of a well-defined model material, sulfonated polystyrene grafted poly(ethylene-alt-tetrafluoroethylene), ETFE-g-PS(SA), we show that the performance and stability of radiation-grafted PEMs in fuel cells strongly depends on the microstructure of the underlying base polymer. The nanoscale structure of the base polymers, grafted films, and membranes is probed by small-angle scattering, and the nanoscale proton dynamics is probed by quasi-elastic neutron scattering. The results of these techniques correlated with fuel cell relevant propertiesincluding proton conductivity and water uptakeand fuel cell performance clearly indicate that differences in the arrangement of the crystalline phase in the otherwise chemically identical semicrystalline base films can have considerable impact, representing an essential aspect to consider in the development of proton exchange membranes prepared via preirradiation grafting.

Radiation-grafted anion-exchange membranes: the switch from low- to high-density polyethylene leads to remarkably enhanced fuel cell performance

“…This is a dramatic demonstration of the findings by Sproll et al related to the development of RG-proton-exchange membranes (RG-PEM), 12 who reported that conductivities, water uptakes, and resulting fuel cell (PEMFC) performances strongly depend on the micro-structure of the ETFE-base films used. The use of nominally identical base ETFE films (from two suppliers), differing only in microstructure, resulted in critical differences in the final membranes: larger crystalline sizes led to enhanced RG-PEM conductivities and durabilities of the resulting PEMFCs.…”

Scaling the Graft Length and Graft Density of Irradiation‐Grafted Copolymers

“…The corresponding characteristic distances are quite similar for both PEMs, which reflects that the swelling of the base film is due to the grafted polymer . This characteristic distance is, however, slightly larger for the L‐PEM (approx.…”

“…15 wt% with an average crystallite size of approx. 9 nm . To enhance scattering from the ionic groups located exclusively in the grafted domains, both PEMs were converted into the Cs‐salt form as outlined in ref .…”

“…34 and 32 nm for L and H, respectively; for comparison, the characteristic distance is approx. 25 nm in the base film) …”

SAXS Investigation on Morphological Change in Lamellar Structures During Propagation Steps of Graft‐Type Polymer Electrolyte Membranes for Fuel Cell Applications

“…This radiation technique allows us to introduce various functional grafted polymers directly bonded to the main chains of polymer substrates, while the inherent characteristics of the polymer substrates such as thermal stability, mechanical strength, and crystallinity are still retained. Morphology of the graft‐type PEMs prepared by the above radiation grafting technique has been intensively investigated using the small‐angle scattering methods with various matrix polymers of poly(tetrafluoroethylene) (PTFE), poly(ether ether ketone) (PEEK), poly(vinylidene fluoride) (PVDF), and poly(ethylene‐ co ‐tetrafluoroethylene) (ETFE) . Consequently, various general features have been well‐established as follows.…”