Chy-Ming Tang

Synthesis and characterization of polyaryl blend membranes having different composition, different covalent and/or ionical cross-linking density, and their application to DMFC☆

Abstract In this contribution, differentionomer blend membrane types which show high proton conductivity, thermal stability, and good direct methanol fuel cell (DMFC) performance, are presented: (1) Covalently cross-linked blend membranes from polyaryl sulfinates and polyaryl sulfonates where the sulfinate groups were crosslinked by alkylation with 1,4-diiodobutane; (2) ionically cross-linked blend membranes from polyaryl sulfonates and poly(het)aryl N bases; (3) covalent-ionically cross-linked blend membranes from polyaryl sulfinates, polyaryl sulfonates, and poly(het)aryl N bases; and (4) blend membranes which additionally contain an inorganic compound. The inorganic compound was mixed into the membrane. As aryl polymers, different poly(ethersulfone)s and different poly(etherketone)s have been used, as hetaryl N base, polybenzimidazole PBI Celazole® has been applied. The membrane characterization yielded the following results: (1) high proton conductivities of the membranes could be realized; (2) the TEM micrographs showed that phase-separated or homogeneous morphologies could be realized in the membranes; (3) the DMFC application of the membranes showed that the developed nonfluorinated ionomer membranes have a DMFC performance comparable to perfluorinated ionomer membranes, reaching peak power densities of around 0.25 W/cm 2 at 110°C. It was also found that the addition of SiO 2 powder dramatically reduced the MeOH permeability, but also led to a worse DMFC performance, probably caused by a worse contact membrane-electrode because of a rougher membrane surface caused by the inorganic compound.

Development and characterization of sulfonated-unmodiftied and sulfonated-aminated PSU Udel® blend membranes

Abstract In the presented work, PSU Udel® which is a chemically and thermally stable arylene main-chain polymer was modified via the metalation-sulfochlorination (-esterification,-sulfonamide formation) and the metalation/amination route. The aminated PSU was stepwise alkylated to yield PSU with (a) -secondary and (b) tertiary amino groups. PSU(SO 2 X) (XCl, OCH 3 , NHC 3 H 7 ) was hydrolysed with hot water or hot diluted sulfuric acid. From the modified polymers membranes were formed by blending the polymers as follows: (a) unmodified PSU/sulfochlorinated PSU; (b) PSU/PSU-SO 2 OCH 3 ; (c) PSU/PSU-SO 2 NHC 3 H 7 . At these blends only physical crosslinking between the polymers occurs by entanglement of the blend components. (d) Li-sulfonated PSU/aminated PSU (PSU-NH 2 ). (e) Li-sulfonated PSU/monomethylaminated PSU (PSU-NH(CH 3 ). (f) Li-sulfonated PSU/di-methylaminated PSU (PSU-N(CH 3 ) 2 ). At the blend membranes (d)–(f) specific interactions beween the polymer components occur by hydrogen bridges and - after acidic post-treatment (see below) -polysalt formation by proton transfer from the SO 3 H to the amino group. The PSU/nonionic sulfonic acid precursor membranes were subsequently hydrolyzed to yield PSU/PSU-SO 3 H blend membranes. It was observed that the membranes containing PSU-SO 2 NHC 3 H 7 could be hydrolyzed only to a small extent to the sulfonic acid under the applied hydrolysis conditions. The blend membranes (d)–(f) were post-treated in 10% HCl to obtain the H + form of the membranes. The ion-exchange capacity of the blends was adjusted by variation of the substitution degree of the modified polymers and by variation of the blend composition. The membrane-blends were characterized by impedance spectroscopy, thermogravimetry and by transmission and scanning electron microscopy. From the investigations it can be concluded that it is advantageous for the mechanical stability of the blends when there is not only entanglement between the polymeric chains of the blend components (as it is the case for the blend membranes (a)–(c)). The swelling degree of the acid-base blends (d)–(f) is lower than the swelling degree of the blends (a)–(c) at the same ion-exchange capacity, leading to better mechanical stability of the acid/base blend membranes (d)–(f).