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Proton-Exchange Membrane Fuel Cells are an alternative source of electricity generation for automobiles and stationary power plants. With increasing concerns on environmental issues, recent research has focused on maximizing the efficiency and durability as well as minimizing the costs of fuel cells. One of the main areas of research is optimizing the structure of the cathode catalyst layer. The main driving force of this thesis was the effective visualization of nanostructure of the ionomer, which is responsible for proton conduction in the cathode catalyst layer. However, challenges regarding sample preparation and radiation damage still need to be well understood. Different sample preparation techniques of catalyst inks and catalyst coated membranes were used for Scanning and Transmission Electron Microscopy, such as freeze fracturing, ultramicrotomy and Focused Ion Beam. Comparisons of the microstructure and chemical differences of all components, especially the ionomer, prepared by ultramicrotomy and Focused Ion Beam, was done with Transmission Electron Microscopy and Scanning Transmission X-ray Microscopy applied to the same catalyst coated membrane sample. Detailed spectroscopic information regarding components in both specimens was compared with C 1s and F 1s near edge X-ray absorption spectra recorded in a Scanning Transmission X-ray Microscope. Focused Ion Beam causes extensive damage to the carbon support and ionomer but prepares thinner sections than ultramicrotomy. This work makes it possible to understand the limitations of each sample preparation and compositional analysis technique in order to later apply one of them to image the ionomer in the catalyst layer at the nanoscale, hopefully using tomography techniques. / Thesis / Master of Materials Science and Engineering (MMatSE)

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In this dissertation, novel approaches to PEMFC durability research are summarized. These efforts are significantly different from most other studies on durability in that rather than focusing on chemical degradation, more attention is given to the mechanical aspects of the PEMFC system. The tensile stress-strain behavior of Nafion® 117 (N117) and sulfonated poly(arylene ether sulfone) random copolymer (BPSH35) membranes is explored under ambient conditions, with respect to the effects of initial strain rate, counterion type, molecular weight and the presence of inorganic fillers. A three-dimensional "bundle-cluster" model is proposed to interpret the tensile observations, combining the concepts of elongated polymer aggregates, proton conduction channels as well as states of water. The rationale focuses on the polymer bundle rotation/interphase chain readjustment before yielding and polymer aggregates disentanglement/ reorientation after yielding. In addition, the influence of uniaxial loading on proton conductivity of N117 and BPSH35 membranes is investigated. When the membranes are stretched, their proton conductivities in the straining direction increase compared to the unstretched films, and then relax exponentially with time. The behavior is explained on the basis of the morphological variations of hydrophilic channels, accompanied by the rotation, orientation and disentanglement of the copolymer chains in the hydrophobic domains, as illustrated with the help of our bundle-cluster model. Finally, the long-term aging of hydrogen-air PEMFCs is examined with a cyclic current profile and under constant current conditions. The end-of-period diagnosis is performed for both MEAs at 100h aging intervals, including a series of cell polarization, impedance and electrochemical experiments. The results demonstrate that hydrogen crossover is the most significant result of degradation for the MEA under cyclic aging mode due to the formation of pinholes at approximately 500-600h, and mass transport limitations are the major degradation sources for constant current mode. A phenomenological mathematical model is set up to describe the PEMFC aging process under both cyclic and constant conditions. / Ph. D.

Poisoning of the catalyst seems to be one of the most serious problems preventing a widespread commercialization of fuel cell technology. This thesis focuses on the effect of CO poisoning and hydrogen dilution by nitrogen on performance of fuel cells with low platinum content. Catalysts were deposited by magnetron sputtering directly on membrane etched by plasma. Alloys with different platinum-ruthenium ratio were used to mitigate the CO poisoning. We found that presence of nitrogen has almost negligible effect on the fuel cell performance. On the other hand, CO, even in small concentrations, caused a significant drop in power density. PtRu with atomic ratio 2:1 and 1:1 showed the best CO tolerance.

Dealloying refers to the partial, selective dissolution of the less noble component(s) of a binary or ternary alloy precursor, resulting in a noble-rich, porous structure that has high surface area. Such surface structure is beneficial for fuel cells (FC) because FC uses platinum (Pt), a scarce metal, to catalyze the oxygen reduction reaction (ORR) at the cathode surface. In order to characterize the benefit of the dealloying process in FC ORR catalysts with the rotating disk electrode (RDE) technique, a high surface area catalyst support, namely 3M Co’s nanostructured thin film (NSTF), was incorporated into the RDE measurements. NSTF-coated glassy carbon (GC) disks were used in RDE experiments on a Pt/Pt1-xIrx (0.05 < x < 0.3) composition spread. ORR measurements using NSTF-coated GC disks measure the catalytic properties with the same morphology, composition and surface structure as would be found in a fuel cell. A series of Pt1-xCox and Pt1-xNix (0.5 < x < 0.8) dealloy catalyst precursor films were tested using NSTF-coated GC disks in RDE studies. The value of x in Pt1-xMx (M = Ni, Co) was selected to be high in order to examine the dealloying process. The catalyst films were examined by a RDE test protocol that tracked the surface enhancement factor (SEF) and ORR current densities over a large number of test cycles. The aim was to measure the catalytic performance of the Pt-M materials as dealloying took place. The SEF of the PtCo and PtNi materials increased rapidly at the beginning and reached a plateau as high as 50 cm2/cm2 while the specific ORR activities increased as the initial M content in the catalyst precursor increased. The impact of the dealloying process on morphology was examined by completely dealloying a Pt3Ni7 precursor, deposited on mirror-polished GC disks, at a constant potential. As the dealloying process continued, the SEF of the material increased from about 1 cm2/cm2 to > 30 cm2/cm2 and resulted in the formation of whisker-like structures.

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