Highly sulfonated multiblock copoly(ether sulfone)s for fuel cell membranes

Abstract

Highly sulfonated multiblock copoly(ether sulfone)s applicable to proton electrolyte fuel cells (PEFCs) were synthesized by the coupling reaction of corresponding hydroxyl‐ terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender, followed by postsulfonation with concentrated sulfuric acid. Their molecular weights were reasonably high as determined by viscosity measurement (ηinh = 0.72–1.58 dL/g). It was also confirmed that postsulfonation selectively took place in hydrophilic segments to yield highly sulfonated multiblock copolymers (IEC = 1.90–2.75 mequiv/g). The resulting polymers gave transparent, flexible, and tough membranes by solution casting. The 4b membrane, as a representative sample, demonstrated good mechanical strength in the dry state regardless of high IEC value (2.75 mequiv/g). The 4a–c membranes with higher IEC values (IEC = 2.75–2.79 mequiv/g) maintained high water uptake (13.7–17.7 wt %) at 50% RH and it was still high (7.4–8.5 wt %) at 30% RH. Proton conductivity of all membranes at 80 °C and 95% RH was higher than that of Nafion 117. Furthermore, the 4a membrane showed high proton conductivity, comparable with Nafion 117 in the range of 50–95% RH, and maintained high proton conductivity (2.3 × 10−3 S/cm) even at 30% RH. Finally, the surface morphology of the membrane was investigated by tapping mode atomic force microscopy, which showed well‐connected hydrophilic domains that could work as proton transportation channel. This phase separation and the high water uptake behavior probably contributed to high and effective proton conduction in a wide range of relative humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2757–2764, 2010

A new class of highly-conducting polymer electrolyte membranes: Aromatic ABA triblock copolymers

“…Other samples showed a similar tendency, which was in accordance with the behavior reported for multiblock sulfonated copolymers. [19][20][21][22] However, unlike the previously reported random or multiblock copolymers, [3] in which higher temperature induced excessive swelling, the temperature had less of an influence on the water uptake and dimensional swelling of 3 membranes, as shown in especially when compared with other copolymer systems at this temperature difference. [3,48,49] Although each sulfonic acid group was solvated by about 26 water molecules, at reduced relative humidity and elevated temperature, a similar but higher water uptake tendency compared with Nafion 112 was observed (Figure 7a).…”

“…These strategies have included changes in the acidity and the position of sulfonic acid groups, and the control of membrane morphologies. [6,[12][13][14] More recently, densely sulfonated [15][16][17][18] or sequenced hydrophilic -hydrophobic multiblock copolymers have been explored for this purpose, [19][20][21][22] but relatively little research on this class of copolymers has been done and the precise control of nanoscale morphology of multiblock copolymers may be limited due to block polydispersity. [23] Therefore, a remaining challenge in the materials science of membranes lies in the molecular design of proton-conducting nanochannels with optimized properties similar to the well-known perfluorinated polyelectrolytes.…”

A clustered sulfonated poly(ether sulfone) based on a new fluorene-based bisphenol monomer

“…One of the effective strategies is the design of multiblock PEMs based on hydrophilic and hydrophobic oligomers. [21][22][23][24][25][26][27][28] The sequential block structure of 45 these PEM promotes phase separation between hydrophilic and hydrophobic segments, resulting in much higher proton conductivity being achieved in a reduced humidity environment in comparison with random sulfonated copolymers. Some multiblock PEMs with long hydrophilic and hydrophobic block 50 segments exhibited clear lamellar morphology with wellconnected hydrophilic channels and proton conductivity comparable to that of Nafion 212 at low humidity.…”

“…Some multiblock PEMs with long hydrophilic and hydrophobic block 50 segments exhibited clear lamellar morphology with wellconnected hydrophilic channels and proton conductivity comparable to that of Nafion 212 at low humidity. [25][26][27] The synthetic route for these multiblock copolymers often requires a multi-step reaction, and it is not easy to control the length of 55 hydrophilic and hydrophobic block oligomers.…”

Sulfonated hydrocarbon membranes for medium-temperature and low-humidity proton exchange membrane fuel cells (PEMFCs)

“…Ueda and co-workers extended their multiblock copolymer structures to the concept of sulfonated hydrocarbon PEMs with high IEC [133]. In their study, using addi-tional post-sulfonation reaction with concentrated sulfuric acid to the multiblock copolymer structure in Fig.…”