An important challenge for PEMFC is stability and durability of the membrane separator. In this dissertation, we applied both experimental and modeling methods to investigate the chemical durability of PFSA membranes for fuel-cell applications. Degradation data were collected after Fenton's tests and the membrane samples were analyzed by XPS after Fenton's test; FTIR was also invoked to validate the XPS results. The effects of Fe2+ concentration and temperature on membrane degradation were discussed. The experimental results provide evidence of chemical attack of the CF2 backbone. Since the level of H2O2 was found to be key to membrane degradation, we designed a novel spectrophotometric method to quantitatively determine H2O2 concentration in a fuel cell by using a multilayer MEA. In addition, a model for H2O2 formation, transport, and reaction in PEMFCs is established for the first time to validate experimental data and study formation mechanism. The humidity effect on membrane degradation was studied by collecting vent water during the tests. The membrane conductivities and mechanical properties were measured by ex-situ high-throughput instruments. FTIR was applied to study both the formation of new groups and the relative abundance of existing groups in the degraded membrane. The thermal stability of degraded membranes was determined by TGA. The cross section of a degraded MEA sample was imaged with SEM to investigate the mechanical structure change. The effect of temperature on membrane degradation was also investigated. XPS spectra were collected from both anode and cathode sides of fuel-cell membrane to compare the effect of temperature on each side. Atomic analysis was performed to study the impact of temperature on both backbone decomposition and side group degradation. A multilayer MEA was used to study the effects of location and thickness on membrane degradation. An improved kinetic model of membrane degradation was built to simulate the experimental data. Finally, an attempt to mitigate membrane degradation by using peroxide decomposition reagent was performed. OCV curves were recorded during two fuel-cell durability tests with and without the addition of this additive. Both FER and TER were compared. Recommendations for the improvement of peroxide decomposition additive were suggested.

Durability of carbon-supported platinum nanoparticle is one of the limiting factors for PEM fuel cell commercial applications. In our research work, we applied both experimental and mathematical simulative tools to study the mechanisms of Pt/C catalyst degradation. An accelerated catalyst degradation protocol by cycling the cathode potential in a square-wave profile was applied to study the losses of cell performances, catalyst ORR activity, and Pt active surface areas. Post-mortem analyses of cathode Pt particle size by X-ray diffraction and platinum distributions in CCMs by SEM/EDS were also conducted. Increased cell temperature and relative humidity was found to accelerate the cathode catalyst degradation. High membrane water contents or abundant water/ionic channels within the polymer electrolyte were believed to accelerate Pt ion transport and cathode degradation. After degradation tests, significant amount of Pt loss into the membrane forming a Pt "band" was observed through cathode platinum dissolution and chemical reduction of soluble Pt ions by permeated hydrogen from the anode. Platinum deposition was confirmed at a location where the permeated hydrogen and oxygen had the complete catalytic combustion over the deposited Pt clusters/particles as the catalyst. A cathode degradation model was built including the processes of platinum oxidation, dissolution/replating, diffusion of Pt ions and Pt band formation in electrolyte. A simplified bi-modal particle size distribution was applied with equal numbers of small and large type particles uniformly distributed in the cathode initially. Processes of Pt mass exchange between two types of particles were demonstrated to cause the overall particle growth. This was due to the particle size effect that platinum dissolution from the small type particles and replating of Pt ions onto the large particles was favored. Parametric study found the increased upper cycling potential was the dominated factor to accelerate the catalyst degradation. Also high frequency of potential cycle and low surface oxide coverage accelerated the degradation rate. Pt dissolution and oxidation processes in perchloric acid were preliminary investigated, and both chemical and electrochemical processes of oxidation and dissolution were believed to be involved under closed-circuit fuel cell conditions with oxygen presence at cathode.

Thesis (Ph. D.)--Ohio State University, 2008.

Made available in DSpace on 2014-10-09T12:28:39Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:29Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les piles à combustibles sont une alternative à l’utilisation de ressources fossiles. Cependant, l’énergie qu’elles produisent reste chère et les procédés de fabrication actuels ne sont pas adaptés à des productions à grande échelle. Une piles de type PEMFC (Proton Exchange Membrane Fuel Cell) essont un système constitué de cinq couches dans lequel la membrane et les deux couches de diffusion peuvent être considértestées comme support d’impression et les deux couches actives peuvent être imprimées par des procédés continus.Ce travail démontrea la pertinence du procédé d’impression appelé flexographiquee dans la fabrication de composants de PEMFC. La flexographieCe procédé offre permet de produire de grandes surfaces de production avec peu de perte de matière fonctionnelle. Malgré la faible imprimabilité des supports choisis, elle permit la fabrication des couches actives aux performances similaires à celles fabriquéesites par procédés conventionnels ont pu être réalisées grâce à la flexogaphie. / In a context of fossil fuel shortage and hydrocarbon emission reduction, fuel cells are a promising solution for energy production. However, the cost of the energy they produce remains too expensive to be competitive and the conventional manufacturing processes used limit the scaling up of the production. The core of Proton Exchange Membrane Fuel Cells (PEMFCs) is a stack composed of five constituents, in which the proton exchange membrane and the two gas diffusion layers have potential for being can be considered as used a a printing substrates, and the two catalyst layers can be printed by continuous printing processes.This work demonstrated the relevance of the printing process called flexography for manufacturing fuel cell components. It offers allows larger production with low waste of expensive elements. Despite of the poor printability of the both chosen substrates, the achieved catalyst layers printed by flexography reached similar electrochemical properties than those made by conventional processes.

Magister Scientiae - MSc (Chemistry) / The anode catalyst is one of the important parts of the direct alcohol fuel cell (DAFC); it is responsible for the alcohol oxidation reaction (AOR) takes place at the anode side. Pd has been reported to have good alcohol oxidation reactions and good stability in alkaline solution. Better stability and activity has been reported for Pd alloyed catalysts when compared to Pd. Choosing a suitable alcohol also has an effect on the activity and stability of the catalyst. This study investigates the best catalyst with better AOR and the best stability and also looks at the better alcohol to use between glycerol and ethanol for the five in-house catalysts (20% Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO on multi walled carbon nanotubes) using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectrometry (EIS) and chronoamperometry. HR-TEM and XRD techniques were used to determine the particle size and average particle size, respectively while EDS used to determine elemental composition and ICP was used to determine catalyst loading. It was observed from LSV that PdNiO was the most active catalyst for both ethanol and glycerol oxidation, and it was the most stable in ethanol while PdMn3O4 proved to be the most stable catalyst in glycerol observed using chronoamperometry. The best alcohol in this study was reported to be glycerol having given the highest current densities for all the inhouse catalysts compared to ethanol observed using LSV. From XRD and HR-TEM studies, particle sizes were in the range of 0.97 and 2.69 nm for XRD 3.44 and 7.20 nm for HR-TEM with a little agglomeration for PdMn3O4 and PdMn3O4NiO.

La synthèse et la caractérisation de nouvelles membranes à conduction protonique, pour pile à combustible à membrane échangeuse de proton, ont été réalisées. Une étude sur des molécules modèles a permis de mieux appréhender la stabilité thermique et électrochimique du polyéthersulfone sulfoné (S-PES). Des membranes à base de polyéthersulfone sulfoné greffés à l’octylamine (S-PESOS) et des membranes mixtes à base de S-PESOS et S-PES ont été caractérisées d’un point de vue physicochimique et électrochimique. L’effet de la réticulation chimique sur les propriétés des membranes a été évalué. Les membranes réticulées présentent des bonnes propriétés mécaniques, des conductivités ioniques et une stabilité chimique suffisantes pour être utilisées dans les piles à combustible à membrane échangeuse de proton. L’étude des propriétés de transport dans ces électrolytes acides a été approfondie en corrélant des mesures thermiques avec des mesures électrochimiques, thermodynamiques et les performances en pile. Mots clés: pile à combustible à membrane échangeuse de proton, conductivité ionique, taux de sulfonation, polyéthersulfone. / The synthesis and characterizations of new membranes with for proton exchange membrane fuel cell were carried out. Thermal and electrochemical stability of sulfonated polyethersulfone (S-PES) were studied. Sulfonated polyethersulfone grafted with octylamine (S-PESOS) membranes and binary S-PESOS and S-PES membranes were characterized from a physicochemical and electrochemical point of view. The effect of chemical cross-linking on the membrane properties was evaluated. The cross-linked membranes showed sufficient mechanical properties, ionic conductivities and chemical stability to be used as electrolyte in the proton exchange membrane fuel cell. The proton transport mechanisms, in this acid electrolyte, were deepened correlating thermal and electrochemical properties, thermodynamic measurements and fuel cells performances.

abstract: Current hybrid vehicle and/or Fuel Cell Vehicle (FCV) use both FC and an electric system. The sequence of the electric power train with the FC system is intended to achieve both better fuel economies than the conventional vehicles and higher performance. Current hybrids use regenerative braking technology, which converts the vehicles kinetic energy into electric energy instead of wasting it. A hybrid vehicle is much more fuel efficient than conventional Internal Combustion (IC) engine and has less environmental impact The new hybrid vehicle technology with it's advanced with configurations (i.e. Mechanical intricacy, advanced driving modes etc) inflict an intrusion with the existing Thermal Management System (TMS) of the conventional vehicles. This leaves for the opportunity for now thermal management issues which needed to be addressed. Till date, there has not been complete literature on thermal management issued of FC vehicles. The primary focus of this dissertation is on providing better cooling strategy for the advanced power trains. One of the cooling strategies discussed here is the thermo-electric modules. The 3D Thermal modeling of the FC stack utilizes a Finite Differencing heat approach method augmented with empirical boundary conditions is employed to develop 3D thermal model for the integration of thermoelectric modules with Proton Exchange Membrane fuel cell stack. Hardware-in-Loop was designed under pre-defined drive cycle to obtain fuel cell performance parameters along with anode and cathode gas flow-rates and surface temperatures. The FC model, combined experimental and finite differencing nodal net work simulation modeling approach which implemented heat generation across the stack to depict the chemical composition process. The structural and temporal temperature contours obtained from this model are in compliance with the actual recordings obtained from the infrared detector and thermocouples. The Thermography detectors were set-up through dual band thermography to neutralize the emissivity and to give several dynamic ranges to achieve accurate temperature measurements. The thermocouples network was installed to provide a reference signal. The model is harmonized with thermo-electric modules with a modeling strategy, which enables optimize better temporal profile across the stack. This study presents the improvement of a 3D thermal model for proton exchange membrane fuel cell stack along with the interfaced thermo-electric module. The model provided a virtual environment using a model-based design approach to assist the design engineers to manipulate the design correction earlier in the process and eliminate the need for costly and time consuming prototypes. / Dissertation/Thesis / Masters Thesis Technology 2014

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Made available in DSpace on 2014-10-09T12:26:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:32Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP