Poly(ether ether ketone) grafted with sulfoalkylamine as proton exchange membrane

A series of side-chain-type sulfonated poly(arylene ether ketone)s with high ion exchange capacity (IEC) values were prepared by polycondensation reaction of 4,4′-difluorobenzophenone with 2,2′-bis(3-amino-4-hydroxyphenyl) and bisphenol A, followed by post-grafting reaction using 1,4-butanesultone. For these obtained membranes, sulfoalkylamine functionalized poly(ether ether ketone) (SAm-PEEK)-0.8 with the highest IEC of 3.42 mequiv. g−1 displayed the highest proton conductivity of 0.11 S cm−1 at 25°C and 0.167 S cm−1 at 60°C, respectively. The morphology of these membranes was investigated by transmission electron microscope analysis. The result showed that these membranes exhibited well-connected hydrophilic channels due to their high IEC values and densely populated flexible acid side chains. Owing to their low methanol permeability and high selectivity, SAm-PEEK- x membranes are promising candidates for direct methanol fuel cell applications.

Synthesis, freestanding membrane formation, and properties of novel sulfonated hyperbranched polyimides

A novel six-membered ring hyperbranched polyimide (HBPI) has been synthesized by condensation polymerization of a difunctional monomer, 9,9-fluorenylidenebis(4,1-phenylene)bis(oxy)-4,4′-bis(1,8-naphthalic anhydride) (FBPNA), and a trifunctional monomer, tris(4-aminophenyl)amine (TAPA), at the molar ratio of FBPNA/TAPA = 1:1 in m-cresol at 180°C for 20 h. The resultant HBPI is further modified via end-capping reaction with 4-phenoxy-1,8-anhydride naphthalene (PNA). Post-sulfonation is performed in concentrated sulfuric acid at different temperatures (50, 60, and 70°C) for the pristine HBPI and 50°C for the PNA-modified polyimides to give various sulfonated HBPIs. Freestanding and tough membranes have been successfully fabricated by casting the polymer solutions containing a cross-linker, bisphenol A epoxy resin, at 80°C. The ion exchange capacities of the resultant membranes are in the range of 1.35–2.21 meq g−1 depending on the degree of chemical modification and the sulfonation conditions. Membrane properties such as water uptake, swelling ratio, proton conductivity, and radical oxidative stability are investigated.

High proton conductivity and low fuel crossover polymer electrolyte membranes derived from branched sulfonated poly(ether ether ketone)s and silica sulfonic acid nanoparticles

With the objective of improving water uptake and proton conductivity, silica sulfonic acid (SSA) nanoparticles were successfully prepared via the sulfonation of silica (SiO2) with sulfuryl chloride and a series of branched sulfonated poly(ether ether ketone) (BSPEEK)-based hybrid membranes with varying contents of SSA were fabricated by the solution-casting method as proton electrolyte materials. The hybrid membranes exhibited improved water uptake, excellent thermal stability, and enhanced mechanical strength. Compared with the methanol permeability, with the incorporation of SSA particles, the proton conductivity enhanced more significantly. The selectivity of the hybrid membranes increased with the increasing SSA contents, and the highest value was 8.2 × 105 S s cm−3, which was 2.6 times higher than that of Nafion 117. Therefore, these BSPEEK-SSA hybrid membranes could be considered as promising materials for direct methanol fuel cell applications.