The series of sulfonated poly(arylene ether ketone) (SPAEK) block copolymers with controlled F-oligomer length bearing pendant diphenyl unit were synthesized via a polycondensation reaction. Sulfonation was verified by H NMR analysis to introduce sulfonic acid group selectively and intensively on the pendant diphenyl unit of polymer backbones. The SPAEK membranes fabricated by the solution casting approach were very transparent and flexible with the thickness of ∼50 μm. These membranes with different F-oligomer lengths were investigated to the physiochemical properties such as water absorption, dimensional stability, ion exchange capacity, and proton conductivity. As a result, the SPAEK membranes (X4.8Y8.8, X7.5Y8.8, and X9.1Y8.8) in accordance to increasing the length of hydrophilic oligomer showed excellent proton conductivity in range of 131-154 mS cm compared to Nafion-115 (131 mS cm) at 90 °C under 100% relative humidity (RH). Among the SPAEK membranes, proton conductivity of SPAEK X9.1Y8.8 (140.7 mS cm) is higher than that of Nafion-115 (102 mS cm) at 90 °C under 80% RH. The atomic force microscopy image demonstrated that number of ion transport channels is increased with increase in the length of hydrophilic oligomer in the main chains, and the morphology is proved to be related to the proton conductivity. The synthesized SPAEK membrane exhibited a maximum power density of 324 mW cm, which is higher than that of Nafion-115 (291 mW cm) at 60 °C under 100% RH.

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Summary Organic‐inorganic composite membranes were prepared by introducing silicon dioxide (SiO2) or functionalized SiO2 (ƒ‐SiO2) with various particle sizes into sulfonated poly (arylene ether ketone) (SPAEK) containing pendant groups, and the membrane was manufactured via directly casting which is a cost‐competitive method. The structure and morphology of the composite membranes were confirmed by 1H NMR, FT‐IR, XRD, and FE‐SEM analysis which demonstrated that inorganic nanofillers were successfully introduced. The FE‐SEM surface images showed that SiO2 and ƒ‐SiO2 particles were very well dispersed within the membrane sheets. The water uptake and swelling ratio of the composite membranes including SiO2 or ƒ‐SiO2 almost did not change when compared with the pristine SPAEK membrane. All fabricated membranes demonstrated good thermal/dimensional stabilities, robust mechanical behavior, and excellent proton conductivity. In particular, the SPAEK/ƒ‐SiO2 composite membranes exhibited improved ionic conductivity compared with the pristine membrane at 70% relative humidity (RH) due to hydrogen bonding between ─SO3H groups of functionalized inorganic filler and polymer backbone. Furthermore, the maximum power density of SPAEK/ƒ‐SiO2 reached as high as 273.11 mW cm−2 at 60°C under 70% RH. Therefore, the composite membranes with ƒ‐SiO2 testify to great potential as polymer electrolyte membrane.

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We developed a series of heterocyclic quaternary ammonium-type poly(arylene ether) (PAE) random copolymers with moieties of sulfone, ketone, hexafluoroisopropyl, isopropyl, phenolphthalein, or phenylene to identify differences in the physicochemical properties of the AEM due to polymer backbone structure containing electron-withdrawing groups (EWGs) or electron-donating groups (EDGs). The 1-methyl pyrrolidine (PYR)-PAE membranes containing EDGs exhibited higher hydroxide conductivity compared with PYR-PAE membranes with EWGs due to more distinctly separated ion transport sites, which was confirmed through AFM phase images. The ionic conductivity of all prepared membranes was greater than 89% after an alkaline stability test for 700 h in 2 M KOH at 70 °C, PYR-PAE membranes with EDGs higher than that of EWGs revealed stronger alkaline stability. In particular, the PYR-PAE-PhPh membrane retained the highest alkaline stability of 96.9% due to the steric hindrance effect. In fuel cell operation, the PYR-PAE-PhPh membrane representing EDGs showed a higher power density (109 mW cm −2 ) than that of the PYR-PAE-BPHF membrane (89 mW cm −2 ) and commercial AEM (Fumion-FAA-3, 30 mW cm −2 ). On the basis of these results, we suggest that structural design of the backbone is a critical strategy to develop an AEM with remarkable electrochemical properties and alkaline stability for alkaline fuel cell applications.

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