Date of Award
5-1-2016
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Gao, Yong
Abstract
A novel free radical-based substitution reaction was developed for grafting aromatic/heteroaromatic compounds to perfluorosulfonic acid polymers (PFSAs). Two proton-exchange membranes perfluorobenzoic acid (PFBA) and perfluorobenzenesulfonic acid (PFBSA)—were synthesized for proton-exchange membrane fuel cells via the free radical-based reaction. The physical properties, in-plane ionic conductivities and fuel cell performance of two membranes were investigated. They exhibited different electrochemical and physical properties, possibly due to the formation of unique dimerized/trimerized structure of –CO2H groups in the PFBA membrane. A free radical-based thermolytic reaction under a high temperature (180 oC)/pressure (1000 psi) condition in the presence of TFA and hydrogen peroxide is first demonstrated. A novel perfluorotetrafluoroaniline (PFTFAn) polymer was synthesized from PFSA and 2,3,5,6-tetrafluoroaniline in one step via the thermolytic reaction. After doping H2SO4 in the PFTFAn polymer, a new conjugated acid membrane (H2SO4-doped PFTFAn) was obtained. The H2SO4-doped PFTFAn membrane displayed better chemical stability and mechanical properties than NafionTM due to the removal of –SO3H groups. The second part of this thesis deals with fluoropolymer-based anion-exchange membranes. A new class of coordinated metal/perfluoropolymer type composite membranes were synthesized and characterized for anion-exchange membrane fuel cells (AEMFCs). A membrane comprised of perfluoro(phenyl-2,2’:6’,2”-terpyridine) polymer, ZrO(ClO4)2 nanoclusters, and 2,2’:6’,2”-terpyridine displayed the highest conductivity of 23.1 mS/cm at 60 oC. The chemical stability test of composite membrane showed no conductivity loss after refluxing in 7 M KOH solution at 120 oC for 2,200 h. A H+ coordinated cage-shape molecule with a benzyl group (Bn-proton cage) was designed and synthesized as a base-stable anion-exchange group. By employing the free radical-based reaction, Bn-proton cage was grafted to a fluoropolymer to yield a stable anion-conductive membrane under alkaline conditions. The third part of this thesis is our design, synthesis and test of ionic liquids for reversible SO2 absorption. Novel di-cationic ionic liquids (DILs) were designed and synthesized for SO2 absorption. DILs were found to have better SO2 absorption capabilities than mono-cationic ionic liquids (MILs). A chloride-based DIL comprised of two N-methylimidazolium cations and a PEG9 (HO-(CH2CH2O)9-H) chain could reversibly uptake 3.710 mole SO2 per mole DIL under ambient conditions. The anion, temperature and water impact on SO2 absorption in DILs was investigated. Although replacing chloride with triflate or tosylate groups led to a reduced SO2 absorption for the DILs, a high selectivity against CO2 was observed in CO2 absorption test.
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