Synthesis and properties of multiblock copoly(arylene ether)s containing superacid groups for fuel cell membranes

Abstract

A series of block copoly(arylene ether)s containing pendant superacid groups were synthesized, and their properties were investigated for fuel cell applications. Two series of telechelic oligomers, iodo-substituted oligo(arylene ether ketone)s and oligo(arylene ether sulfone)s, were synthesized. The degree of oligomerization and the end groups were controlled by changing the feed ratio of the monomers. The nucleophilic substitution polymerization of the two oligomers provided iodo-substituted precursor block copolymers. The iodo groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The high degree of perfluorosulfonation (up to 83%) was achieved by optimizing the reaction conditions. Tough and bendable membranes were prepared by solution casting. The ionomer membranes exhib-ited characteristic hydrophilic/hydrophobic phase separation with large hydrophilic clusters (ca. 10 nm), which were different from that of our previous random copolymers with similar molecular structure. The block copolymer structure was found to be effective in improving the proton-conducting behavior of the superacid-modified poly(arylene ether) ionomer membranes without increasing the ion exchange capacity (IEC). The highest proton conductivity was 0.13 S/cm at 80 C, 90% relative humidity, for the block copolymer ionomer membrane with IEC ¼ 1.29 mequiv/g. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: [452][453][454][455][456][457][458][459][460][461][462][463][464] 2011

Perfluorosulfonyl Imide versus Perfluorosulfonic Acid Ionomers in Proton‐Exchange Membrane Fuel Cells at Low Relative Humidity

“…Recently, increasing the acidity of the functional moiety has emerged as a plausible approach to favor proton transport, and significantly higher proton conductivities were reported as compared to those of directly sulfonated aromatic ionomers . The enhanced conductivity was attributed to (i) the higher acidity of the acidic side chains (p K a ≈−6 in perfluorosulfonic acid and p K a ≈−1 in aryl sulfonic acid) inducing higher ability to dissociate proton at low relative humidity (RH); and (ii) the presence of a flexible hydrophobic spacer between the backbone and the acidic function, favoring nano‐phase separated microstructures with well interconnected ionic clusters .…”

“…[7][8][9][10] Recently,i ncreasing the acidity of the functional moiety has emerged as ap lausible approach to favor proton transport, and significantly higher proton conductivities were reported as compared to those of directly sulfonated aromatic ionomers. [11][12][13][14][15][16] The enhanced conductivity was attributed to (i)the highera cidity of the acidic side chains (pK a %À6i np erfluorosulfonica cid and pK a %À1i na ryl sulfonica cid) [17] inducing higher ability to dissociate protona tl ow relative humidity (RH);a nd (ii)the presence of af lexible hydrophobic spacer between the backbonea nd the acidic function, favoring nanophase separated microstructures with well interconnected ionic clusters. [18,19] As ac onsequence, aromatici onomers obtained by combining multiblock structure with perfluorosulfonic acid sidechains with optimized chemical structurea nd membrane manufacturing condition showedi mproved fuel cell performance andd urability as compared to those of Nafion.…”

Synthesis of partially fluorinated poly(arylene ether sulfone) multiblock copolymers bearing perfluorosulfonic functions

“…Consequently, a variety of synthesis strategies aiming at increasing the acidity of the ionic function or/and at improving the membrane morphology has been explored to optimize the conductivity of aromatic ionomers. Regarding the search for increased acidity, aromatic ionomers bearing aryl sulfonimide acid or alkyl perfluoro alkyl sulfonic acid side chains instead of aryl sulfonic acid were recently proposed. The poly(arylene ether)s containing pendant PFSA groups showed more phase‐separated morphology and higher proton conductivity than those of the poly(arylene ether)s with main chain grafted sulfonic acid groups.…”

Proton Conductivity in Doped Aluminum Phosphonate Sponges

“…[5][6][7] Although initial results showed effectively that such solvents could be immobilized onto polymer backbones, the low concentration of functional groups led to rather low proton conductivity values. [8][9][10][11][12][13] Unfortunately, these membranes tend to swell in cases of high ion-exchange capacity, which compromised their mechanical stability.…”