Guerrero-Gutiérrez, Edward M. A.

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    Sulfonated fluoroblock copolymer membranes for direct methanol fuel cell applications
    (2014) Guerrero-Gutiérrez, Edward M. A.; Suleiman-Rosado, David; College of Engineering; Padovani, Agnes M.; Saliceti Piazza, Lorenzo; Estévez, Antonio; Department of Chemical Engineering; Ríos Guillet, Robert
    This investigation studied the transport properties of several fluorinated sulfonated membranes for direct methanol fuel cell applications. First, Nafion® membranes were processed with supercritical fluid (SCF) CO2 and their resulting nanostructure was cross-linked with inorganic materials. Nafion® membranes were exposed to SCF CO2 and a counter ion solution using two different approaches: first, it was processed with SCF CO2, and then exchanged using six different counter ions: Al+3, Fe+3, Ca+2, Ba+2, Cu+2 and K+1. The second method performed the counter ion substitution first, followed by the SCF CO2 processing. Results showed that the incorporation of counter ions into Nafion® influences the ionic domains uniquely for each cation or their combination studied, but also influences the crystallinity, the morphology, and the water swelling properties, which are very important in the transport of protons through the membrane. The processing order (SCF processing vs. counter ion substitution) shows that although the magnitude of the methanol permeability and proton conductivity are affected, the trends are primarily limited by the nature of the counter ion and not by the order of the process. Nafion® membranes were also processed with SCF CO2 and then exchanged using a combination of three different counter ions: Fe+3, Ca+2 and K+1 . In addition, the transport properties of ionic membranes composed of a sulfonated poly(styrene-isobutylene-styrene) (SIBS SO3) with novel fluoropolymers based on poly(styrene) (PS), poly(2,2,3,4,4,4-hexafluorobutyl methacrylate) (PHFBM), poly(4-fluorostyrene), poly(2,3,4,5,6-pentafluorostyrene) (P5FS) and poly(isobutylene) (PIB) were evaluated. Homopolymer, bi, tri and tetra fluoroblock copolymers were synthesized by Atom Transfer Radical Polymerization (ATRP); however, PIB was polymerized by cationic polymerization. Different initiators were employed: two fluoroinitiators, obtained from the esterification of 2-(perfluoroalkyl) ethanol or, octafluoro 4-4’-biphenol; the third initiator evaluated was 1-bromoethyl benzene. The esterified initiators have a significant impact on the thermal stability of PS, PHFBM and the diblock copolymers. The proton conductivity and methanol permeability of SIBS SO3 blend membranes was limited by the nature of the initiator and the interaction of the polymer with the sulfonic group. The proton conductivity of SIBS SO3 blend membrane was limited by the chemical and fluoropolymer composition, the blend morphology and the interaction of the fluoropolymer with the sulfonic group.