A new interpretation of SAXS peaks in sulfonated poly(ether ether ketone) (sPEEK) membranes for fuel cells

Abstract

The structure of a commercial sulfonated poly(ether ether ketone) (sPEEK) membrane was analyzed by Small-Angle X-Ray Scattering (SAXS) for different water uptakes obtained after immersion in liquid water at various temperatures. For low membrane swelling, the SAXS profile displays only a wide-angle peak in the 0.2-0.3 Å(-1) region. As the membrane swells, two supplementary correlation peaks arise and shift towards small angles, which are the signature of a structural evolution of the membrane, whereas the wide angle peak remains stable. The SAXS spectra of sPEEK membranes can thus display three correlation peaks simultaneously. Therefore we propose a new interpretation of these SAXS spectra which conclude that the two small angle peaks are attributed to the so-called matrix and ionomer peaks and the wide-angle peak is ascribed to the mean separation distance between sulfonic acid groups grafted onto the polymer backbone. This peak attribution implies that the sPEEK nano-phase separation is triggered by an immersion in hot water (ionomer peak apparition). Our new peak attribution was confirmed by studying the impact of temperature, electron density contrast and ionic exchange capacity.

Polyelectrolyte microcapsules as ionic liquid reservoirs within ionomer membrane to confer high anhydrous proton conductivity

“…It was found that the addition of ILs shifted the scattering peak to a smaller value, and no peak could be observed in the range of 0.1e0.3 nm À1 . Similar results had been observed in other SPEEKbased membranes [34,37,38]. The reduction of q values was probably attributed to the enrichment of ILs within the hydrophilic clusters, which boarded the clusters and then formed interconnected channels.…”

Nanocomposite Based on Functionalized Gold Nanoparticles and Sulfonated Poly(ether ether ketone) Membranes: Synthesis and Characterization

“…This treatment, applied on the pristine sPEEK membrane, allows the production of a host sPEEK membrane with well-defined and swell hydrophilic domains, suitable for hosting the precursors [54]. By adding the strong reducing agent NaBH 4 to the reaction mixture, after 30 min of impregnation, a rapid color variation was observed, from yellow to brown, and the white translucent sPEEK membranes gained a brown color upon the sorption and reduction process, remaining unchanged upon rinsing.…”

SPEEK‐Tin dioxide proton conducting membranes: Effect of modifying agent of tin dioxide particles surface

“…The presence of the wide peak centered around 0.3 Å −1 has recently been unambiguously attributed to the mean separation distance between the sulfonic acid groups grafted onto the polymer backbone. [ 36 ] In our membranes such distance was around 2π/0.3 = 21 Å.…”

“…[ 36 ] This peak, well‐known as “ionomer peak” in the literature [ 9,36 – 39 ] originates from the spatial correlation distance (around 37 Å in our membranes) between hydrophilic SO 3 H − rich nanodomains (ionic clusters) full of water molecules, which are interconnected by hydrated sulfonated polymer channels, whereas the more hydrophobic nonsulfonated phase constitutes the polymer matrix. The second broad interference peak, so‐called “matrix peak” [ 36 ] was centered around 0.05 Å −1 in the pattern of the pristine SPEEK, which corresponds to a distance of 125 Å, associated to the average distance between polymer nanocrystals. The low spatial correlation between the crystallites, attested by the high broadness of the peak, suggests a low number of crystallites dispersed in the amorphous polymer matrix, which is consistent with the essentially amorphous character of the membrane.…”