Bearing Acid Groups Research Articles

Enhanced thermo-oxidative stability of sulfophenylated poly(ether sulfone)s

Monophenylated poly(ether sulfone)s (Ph-PES) and diphenylated poly(ether sulfone)s (DiPh-PES), were synthesized as starting materials for the preparation of sulfonated polymers with well-defined chemical structure. Mild post-polymerization sulfonation conditions led to sulfonated Ph-PES (Ph-SPES) bearing acid groups on both the pendant phenyl group and the backbone, and sulfonated DiPh-PES (DiPh-SPES) bearing acid groups only on the two pendant phenyl groups. Both series of polymers had excellent mechanical properties, high glass transition temperatures, good thermal and oxidative stability, as well as good dimensional stability. It is interesting to note that exclusively pendant-phenyl-sulfonated (bis-sulfophenylated) DiPh-SPES copolymers possessed obviously better thermal and oxidative stability compared with the corresponding pendant-phenyl-sulfonated/main-chain-sulfonated Ph-SPES copolymers. The methanol permeability values of the membranes were in the range of 7.0 × 10 −7–9.4 × 10 −8 cm 2/s at 30 °C, which is several times lower than that of Nafion 117. DiPh-SPES-50 and Ph-SPES-40 also exhibited high proton conductivity (approximately 0.13 S/cm at 100 °C).

Synthesis and properties of polyimides bearing acid groups on long pendant aliphatic chains

AbstractA series of novel polyimide electrolytes having long pendant sulfo‐ or phosphoalkoxy groups were synthesized for fuel‐cell applications. Sulfodecyloxy‐, phosphodecyloxy‐, and sulfophenoxydodecyloxy‐substituted benzidine monomers were synthesized from dihydroxybenzidine. These monomers were copolymerized with naphthalene tetracarboxylic dianhydride and fluorenylidene dianiline to give the corresponding polyimides. A flexible, ductile, and self‐standing membrane was obtained via casting from the polyimide solution. Because the acid groups were on long pendant side chains and away from the main chains, the polyimide membrane showed improved oxidative and hydrolytic stability in comparison with the polyimides with sulfonic acid groups on the main chains or on the short side chains. High thermal stability (no glass‐transition temperature and a decomposition temperature > 200 °C) was also obtained. The polyimide membrane displayed high proton conductivity of 10−1 S cm−1 at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3995–4005, 2006

Development of porous silicon-based miniature fuel cells

Nowadays the rise in portable electronics requires energy sources compatible with the environmental constraints. We demonstrate, in this paper, how microfabrication techniques allow the development of low-cost miniature fuel cells fully integrated on silicon. Contrary to usual proton-conducting membranes made of ionomers ensuring the proton conductivity of proton-exchange membrane fuel cells (PEMFCs), we present here another way to proceed. It consists in the chemical grafting of molecules bearing acid groups on the pore walls of a porous silicon membrane to mimic the structure of an ionomer, such as Nafion®. We obtain an inorganic, dimensionally stable, proton-conducting membrane with many optimizable parameters such as the pore size and the pore structure of the membrane or the nature of the grafted molecules. Moreover, the use of a silicon substrate offers advantages of serial and parallel integration, the possibility of encapsulation by wafer bonding and gas feed and electrical contacts may be included into the membrane etching process, thanks to simple KOH wet etching processes and metal sputtering.