Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

abstract: Proton exchange membrane fuel cells (PEMFCs) run on pure hydrogen and oxygen (or air), producing electricity, water, and some heat. This makes PEMFC an attractive option for clean power generation. PEMFCs also operate at low temperature which makes them quick to start up and easy to handle. PEMFCs have several important limitations which must be overcome before commercial viability can be achieved. Active areas of research into making them commercially viable include reducing the cost, size and weight of fuel cells while also increasing their durability and performance. A growing and important part of this research involves the computer modeling of fuel cells. High quality computer modeling and simulation of fuel cells can help speed up the discovery of optimized fuel cell components. Computer modeling can also help improve fundamental understanding of the mechanisms and reactions that take place within the fuel cell. The work presented in this thesis describes a procedure for utilizing computer modeling to create high quality fuel cell simulations using Ansys Fluent 12.1. Methods for creating computer aided design (CAD) models of fuel cells are discussed. Detailed simulation parameters are described and emphasis is placed on establishing convergence criteria which are essential for producing consistent results. A mesh sensitivity study of the catalyst and membrane layers is presented showing the importance of adhering to strictly defined convergence criteria. A study of iteration sensitivity of the simulation at low and high current densities is performed which demonstrates the variance in the rate of convergence and the absolute difference between solution values derived at low numbers of iterations and high numbers of iterations. / Dissertation/Thesis / M.S.Tech Chemistry 2011

abstract: With a recent shift to a more environmentally conscious society, low-carbon and non-carbon producing energy production methods are being investigated and applied all over the world. Of these methods, fuel cells show great potential for clean energy production. A fuel cell is an electrochemical energy conversion device which directly converts chemical energy into electrical energy. Proton exchange membrane fuel cells (PEMFCs) are a highly researched energy source for automotive and stationary power applications. In order to produce the power required to meet Department of Energy requirements, platinum (Pt) must be used as a catalyst material in PEMFCs. Platinum, however, is very expensive and extensive research is being conducted to develop ways to reduce the amount of platinum used in PEMFCs. In the current study, three catalyst synthesis techniques were investigated and evaluated on their effectiveness to produce platinum-on copper (Pt@Cu) core-shell nanocatalyst on multi-walled carbon nanotube (MWCNT) support material. These three methods were direct deposition method, two-phase surfactant method, and single-phase surfactant method, in which direct deposition did not use a surfactant for particle size control and the surfactant methods did. The catalyst materials synthesized were evaluated by visual inspection and fuel cell performance. Samples which produced high fuel cell power output were evaluated using transmission electron microscopy (TEM) imaging. After evaluation, it was concluded that the direct deposition technique was effective in synthesizing Pt@Cu core-shell nanocatalyst on MWCNTs support when a rinsing process was used before adding platinum. The peak power density achieved by the rinsed core-shell catalyst was 618 mW.cm-2 , 13 percent greater than that of commercial platinum-carbon (Pt/C) catalyst. Transmission electron microscopy imaging revealed the core-shell catalyst contained Pt shells and platinum-copper alloy cores. Rinsing with deionized (DI) water was shown to be a crucial step in core-shell catalyst deposition as it reduced the number of platinum colloids on the carbon nanotube surface. After evaluation, it was concluded that the two-phase surfactant and single-phase surfactant synthesis methods were not effective at producing core-shell nanocatalyst with the parameters investigated. / Dissertation/Thesis / M.S.Tech Technology 2012

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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