Organic coatings are extensively used as protective coatings in several industries including the automotive and aircraft industries. The last few years have witnessed an increased interest in improving not only the mechanical properties but also the corrosion protection properties of organic coatings. Among the currently investigated methods of improving the performance of organic coatings is the incorporation of additives in the organic paint matrix. Vapor grown carbon nanofibers (VGCNFs) are a class of carbon fibers that are produced by catalytic dehydrogenation of a hydrocarbon at high temperatures. Depending on the method of synthesis and the post-treatment processes, the diameter of the VGCNFs is normally in the 10-300 nm range. The small size, light weight, high aspect ratio, and unique physical, thermal, mechanical, and electrical properties of VGCNF make it an ideal reinforcing filler in polymer matrix nanocomposites to enhance the mechanical properties of the pure polymeric material in high performance applications in several industries such as the automotive, aircraft, battery, sensors, catalysis, electronics, and sports industries. The main objective of the current investigation was to study the corrosion protection offered by the incorporation of VGCNFs into a commercial alkyd paint matrix applied to the surface of mild steel coupons. The corrosion protection was investigated by immersing samples in air saturated 3% NaCl solution (artificial seawater). The samples were studied by electrochemical impedance spectroscopy (EIS) along with other measurements, including electrochemical (open circuit potential, cyclic voltammetry), chemical (salt spray test), electrical conductivity, and surface analysis (SEM, AFM, optical profilometry, and nanoindentation). The study involved the investigation of the effect of the weight percent (wt %) of the VGCNF as well as the coating film thickness on the corrosion protection performance of the coated steel samples when exposed to the corrosive electrolyte. By way of contrast, the EIS behavior of steel coupons coated with a paint coating incorporating different weight percents of powdered silicon carbide (SiC) particles was also studied. The EIS spectra were used to calculated and graph several corrosion parameters for the investigated systems. At the end, the studied coatings were ranked in order of their anticorrosive properties.

Dans ce travail de thèse, deux objectifs ont été fixés. Le premier a été de mieux comprendre le mécanisme très complexe qui est en jeu dans les accumulateurs Li/S. Pour cela, les modifications structurales du matériau actif ont été observées in operando et ont permis de valider un modèle clair concernant les réactions de transformations de phases qui contrôlent le lithium/soufre. La cristallisation d’une forme métastable du soufre (bêta-S8 monoclinique) en fin de recharge a ainsi été observée pour la première fois lors d’expériences au synchrotron de l’ESRF. La technique d’impédance électrochimique a également donné d’importantes informations sur les cinétiques deces réactions. Le deuxième objectif visait l’amélioration du système Li/S par l’optimisation des électrodes de soufre afin d’augmenter leurs performances mais également par la fabrication d’électrodes de Li2S efficaces permettant la transition vers le Li-ion/S, plus sécuritaire. / In this work two main aspects has been conducted in parallel. The first one was focused on betterunderstanding the very complex working mechanism of Li/S cell. Structural changes evolution ofactive material upon real time battery operation was explored, giving a clear answer on thesolid/liquid reaction evolution, which govern the electrochemistry of Li/S technology. Formationof another allotropic form of sulfur (monoclinic beta-S8) during recharging the battery have beenreported for the first time ever in Li/S community. Impedance technique applied to such systemprovided additional information concerning the kinetics of these reactions. Apart from that,another aspect targeted rather on improvements of already existing solutions (making better sulfurelectrodes, with significantly improved specific capacities) as well as development the alternativesolutions, i.e. fabrication and test of new Li2S-based positive electrodes, which could be apromising transition from classical Li/S cells into safer Li-ion/S batteries.

Abstract : The objectives of this work were to prepare and characterize films of benzylic amide macrocycles and rotaxanes obtained by functionalisation of an acidterminated self-assembled monolayer (SAM) on gold, and thus to probe the aptitude of these surfaces for applications in the field of the nanotechnologies. We initially studied the self-assembled monolayer of 11-mercaptoundecanoic acid and focused on its composition, structure and organization. We show that the molecules of alcanethiol are oriented with the acid group pointing out from the surface. The film is highly ordered with defect density below 0.2%. We investigated the functionalisation process with the covalently bound Mac-OH macrocycle, with the physisorbed Mac-pyridine macrocycle and with the naphtalimide rotaxane. The latter is also anchored to the SAM through a non-covalent interaction. We focused on the comprehension of both quantitative as qualitative characteristics of the films, such as the degree of functionalisation, their stability with respect to external constraints, their order and homogeneity, their structure and their orientation. By combining techniques such as X-ray photoemission spectroscopy, infrared reflection-absorption spectroscopy, atomic force microscopy, electrochemical and contact angle measurements, we demonstrated that the films of macrocycles reach a high degree of functionalisation. The layers are homogeneous and a preferential orientation of the macrocycle molecules with the plan of the ring tilted with respect to the surface and with the alkyl chains pointing-out from the films is observed. In addition, we studied the possibility of using the macrocycle films for molecular recognition, employing the Fc-Gly-Gly molecule as a model target. Through similar experiments and analysis, films of naphtalimide rotaxane were proven to give a good functionalisation of SAM. The molecule adsorbs with a preferential orientation of the linear axis parallel to the surface and the macrocycle unit normal to it. We characterized the fluorescent properties of the molecule due to the naphtalimide group and showed that when adsorbed on a gold substrate the presence of the self-assembled monolayer prevents total quenching. <br> Résumé : Les objectifs de ce travail étaient de caractériser des films de macrocycles et de rotaxanes de type amide benzylique obtenus par la fonctionnalisation de monocouches auto-assemblées d'alcanethiols, ayant un groupe acide terminal, sur une surface d'or, et ainsi de mettre en évidence certaines des potentialités de ces surfaces en vue d'applications éventuelles dans le domaine des nanotechnologies. Nous avons d'abord étudié la monocouche auto-assemblée de l'acide 11-mercaptoundecanoïque et particulièrement les aspects tels que la composition, la structure et l'organisation du film et nous avons mis en évidence que les molécules d'alcanethiol sont orientées dans le film avec le groupe acide vers l'extérieur de la surface, de façon à pouvoir interagir avec les molécules à greffer, et que le degré d'ordre de la monocouche est très élevé, en montrant celle-ci une fraction de défauts inférieure au 0.2% de l'aire totale du film. L'étude de la fonctionnalisation successive avec le macrocycle Mac-OH, lié de façon covalente, et le macrocycle Mac-pyridine ainsi que la rotaxane naphtalimide, ancrés à travers une interaction non-covalente à la monocouche auto-assemblée, a porté une attention particulière à la compréhension d'aspects tels que le degré de recouvrement de la surface, la stabilité vis-à-vis de contraintes externes, l'ordre et l'homogénéité, ainsi que la structure des films et l'orientation des molécules. Grâce à la combinaison de techniques telles que l'XPS, l'IRAS, les techniques électrochimiques, les mesures d'angle de contact et l'AFM, nous avons mis en évidence que les films de macrocycle atteignent un recouvrement élevé et homogène de la monocouche autoassemblée et qu'une orientation des molécules de macrocycle, avec une inclinaison du plan de l'anneau par rapport à la surface et pointant leurs chaînes alkyles vers l'extérieure du film, est observée. Ensuite, nous avons abordé la possibilité d'impliquer les films de macrocycle en tant que récepteurs moléculaires d'une molécule modèle, la Fc-Gly-Gly. Par une caractérisation similaire, les films de la rotaxane naphtalimide ont montré d'atteindre un recouvrement élevé de la surface de la monocouche avec une orientation privilégiée des molécules avec l'axe parallèle et le macrocycle perpendiculaire à la surface pour pouvoir interagir, à travers les fonctions pyridine du macrocycle, avec la monocouche. De plus, nous avons caractérisé les propriétés fluorescentes de la molécule, résidantes dans son groupe naphtalimide, lorsqu'elle est adsorbée sur un substrat métallique, l'or, affectées par la présence de la monocouche auto-assemblée.

In this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines.

In this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines.

In this thesis, the focus is on studying BaZrO3-BaCeO3 based proton conductors due to that they represent very promising proton conductors to be used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs). Here, dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics were selected as the major studied materials. These ceramics were prepared by different sintering methods and doping strategies. Based on achieved results, the thesis work can simply be divided into the following parts: 1) An improved synthesis method, which included a water-based milling procedure followed by a freeze-drying post-processing, was presented. A lowered calcination and sintering temperature for a Hf0.7Y0.3O2-δ (YSH) compound was achieved. The value of the relative density in this work was higher than previously reported data. It is also concluded that this improved method can be used for mass-production of ceramics. 2) As the solid-state reactive sintering (SSRS) represent a cost-effective sintering method, the sintering behaviors of proton conductors BaZrxCe0.8-xLn0.2O3-δ (x = 0.8, 0.5, 0.1; Ln = Y, Sm, Gd, Dy) during the SSRS process were investigated. According to the obtained results, it was found that the sintering temperature will decrease, when the Ce content increases from 0 (BZCLn802) to 0.3 (BZCLn532) and 0.7 (BZCLn172). Moreover, the radii of the dopant ions similar to the radii of Zr4+ or Ce4+ ions show a better sinterability. This means that it is possible to obtain dense ceramics at a lower temperature. Moreover, the conductivities of dense BZCLn532 ceramics were determined. The conductivity data indicate that dense BZCY532 ceramics are good candidates as either oxygen ion conductors or proton conductors used for ITSOFCs. 3) The effect of NiO on the sintering behaviors, morphologies and conductivities of BZCY532 based electrolytes were systematically investigated. According to the achieved results, it can be concluded that the dense BZCY532B ceramics (NiO was added during ball-milling before a powder mixture calcination) show an enhanced oxygen and proton conductivity. Also, that BZCY532A (NiO was added after a powder mixture calcination) and BZCY532N (No NiO was added in the whole preparation procedures) showed lower values. In addition, dense BZCY532B and BZCY532N ceramics showed only small electronic conductivities, when the testing temperature was lower than 800 ℃. However, the BZCY532A ceramics revealed an obvious electronic conduction, when they were tested in the range of 600 ℃ to 800 ℃. Therefore, it is preferable to add the NiO powder during the BZCY532 powder preparation, which can lower the sintering temperature and also increase the conductivity. 4) Dense BZCY532 ceramics were successfully prepared by using the Spark Plasma Sintering (SPS) method at a temperature of 1350 ℃ with a holding time of 5 min. It was found that a lower sintering temperature (&lt; 1400 ℃) and a very fast cooling rate (&gt; 200 ℃/min) are two key parameters to prepare dense BZCY532 ceramics. These results confirm that the SPS technique represents a feasible and cost-effective sintering method to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors. 5) Finally, a preliminary study for preparation of Ce0.8Sm0.2O2-δ (SDC) and BZCY532 basedcomposite electrolytes was carried out. The novel SDC-BZCY532 based composite electrolytes were prepared by using the powder mixing and co-sintering method. The sintering behaviors, morphologies and ionic conductivities of the composite electrolytes were investigated. The obtained results show that the composite electrolyte with a composition of 60SDC-40BZCY532 has the highest conductivity. In contrast, the composite electrolyte with a composition of 40SDC-60BZCY532 shows the lowest conductivity. In summary, the results show that BaZrO3-BaCeO3 based proton-conducting ceramic materials represent very promising materials for future ITSOFCs electrolyte applications. / <p>QC 20150423</p>

Ce travail de thèse est consacré à l’étude des nickelates La2-xPrxNiO4+δ, comme nouveaux matériauxde cathodes pour piles à combustible haute température, SOFC, et en particulier à la caractérisationde leur stabilité chimique et leur comportement en fonctionnement. En effet, du fait de leurpropriété de conduction mixte ionique et électronique, MIEC, les nickelates de structure typeK2NiF4, Ln2NiO4+δ (Ln = La, Pr, Nd), correspondant au terme n = 1 de la série de Ruddlesden-Popper (An+1MnO(3n+1)), sont des matériaux prometteurs pour des fonctionnements à températureintermédiaire, IT-SOFC (T < 800 °C). Compromis entre la stabilité chimique de La2NiO4+δ et lestrès bonnes performances électrochimiques de Pr2NiO4+δ, les phases La2-xPrxNiO4+δ, ont étésynthétisées et leurs propriétés physico-chimiques, de transport et électrochimiques ont étédéterminées. L’étude approfondie des caractéristiques des électrodes par spectroscopied’impédance en cellules symétriques a été réalisée à courant nul et sous polarisation anodique etcathodique sur des périodes d’un mois. De façon surprenante, même après la dissociation complètede Pr2NiO4+δ en PrNiO3-δ, Pr4Ni3O10+δ et Pr6O11, la résistance de polarisation ne montre pas dechangement significatif. L’étude de PrNiO3-δ et Pr4Ni3O10+δ, comme matériau de cathode pour pilesà combustible, démontre l’excellent comportement de la phase Pr4Ni3O10+δ et ceci en cellulesymétrique (Rp (Pr4Ni3O10+δ) = Rp (Pr2NiO4+δ) = 0.15 Ω.cm² à 600 ° C) et cellule complète (1.6W.cm-2 at 800 °C). / This PhD work is dedicated to stability and ageing studies of Praseodymium based nickelates ascathodes for Solid Oxide Fuel Cells (SOFCs). With this respect Ln2NiO4+δ (Ln=La, Pr or Nd)compounds with the K2NiF4 type structure act as alternative cathode materials for IT-SOFC due totheir mixed ionic and electronic conductivity (i.e. MIEC properties). Pr2NiO4+δ shows excellentelectrochemical properties at intermediate temperature (i.e. low polarization resistance Rp value, Rp= 0.03 Ω.cm² at 700 °C), while La2NiO4+δ exhibits higher chemical stability. So, the properties ofLa2-xPrxNiO4+δ nickelates were investigated with the aim to find best compromise between chemicalstability and electrochemical performances. After synthesis, the physical and chemical properties aswell as their transport and electrochemical properties have been determined. Measurements of thepolarization resistance of symmetrical half-cells have been carried out by impedance spectroscopy.Then, the chemical stability and the electrochemical performance of the materials have been studiedfor duration up to one month. As an interesting point, even after complete dissociation of Pr2NiO4+δinto PrNiO3-δ,Pr4Ni3O10+δ and Pr6O11, the polarization resistance does not show significant change.So finally, two new materials PrNiO3-δ and Pr4Ni3O10+δ were investigated as SOFCs cathodeshowing very promising results for Pr4Ni3O10+δ in symmetrical cell (Rp (Pr4Ni3O10+δ) = Rp(Pr2NiO4+δ) = 0.15 Ω.cm² à 600 ° C) and complete cell (1.6 W.cm-2 at 800 °C).

Magister Scientiae - MSc / In this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines. / South Africa

This work investigates the correlation of structural and photovoltaic properties of dyes used in dye-sensitized solar cells. Experimental methods, including ultraviolet-visible spectroscopy, fluorescence spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy are employed to study optical and electrochemical properties of dye molecules. Computational methods, including density functional theory and time-dependent density functional theory, are used to validate and predict the optical and electronic properties of dye molecules, in their isolated state and once embedded into a working electrode device environment that comprises a dye...TiO2 interface. The results chapters begin with the presentation of a series of quinodimethene dyes that are experimentally validated for their photovoltaic application, and associated computational studies reveal that an inner structural factor - a phenyl ring rotation occurring during the optical excitation process - leads to the competitive photovoltaic device performance of these dyes. Carbazole-based dyes are then systematically studied by computation, especially considering charge transfer paths and binding modes of these dyes on a titania surface. The theoretical models for the basic building block of this chemical family of dyes, known as MK-44, successfully support and explain structural discoveries from X-ray diffraction and reflectometry that impact of their function. A benzothiadiazole-based dye, RK-1, is then systematically studied by both experimental and computational methods, and the results show that the π-bridge composed of thiophene, benzothiadiazole and benzene rings leads to excellent charge separation; and the rotation of these rings during the optical excitation process may well be consistent with the fluorescence spectrum. Finally, the well-known ruthenium-based dyes are theoretically studied to determine the properties of different ligands connected to the metal core of the complex. Conformations with different NCS ligands are calculated in terms of energy and explain well the corresponding results from X-ray diffraction. Acid-base properties of carboxyl groups connected to pyridine ligands in N3 and N749 are theoretically calculated based on thermodynamics and density functional theory. Implicit and explicit models are both adopted to predict these acid dissociative constant values, which are generally in a good agreement with the reported experimental data. The thesis concludes with conclusions and a future outlook.

Cette thèse se positionne dans le domaine des batteries lithium-ion. Elle a pourobjectif de mieux comprendre le fonctionnement de l’électrode négative de graphiteen étudiant le processus de formation du film de passivation, couramment appeléSEI (Solid Electrolyte Interface) créé à l’interface avec l’électrolyte. Ce travail nousa conduit à proposer des modèles pouvant expliquer comment se forme la SEI et àidentifier les phénomènes qui entrent en jeu dans le fonctionnement de la batterie.La SEI résulte de la réaction entre l’électrode de graphite, les ions lithium et les moléculesorganiques de l’électrolyte qui survient lors du premier processus d’insertion.Elle est principalement composée des produits de décomposition de l’électrolyte etles ions lithium consommés ne sont plus échangeables. Elle est donc responsable dela capacité irréversible observée lors du premier cycle de formation, correspondantà la différence de capacité entre le processus d’insertion et le processus de désinsertion.Il est donc essentiel de mieux comprendre les paramètres qui l’influencentpour pouvoir ainsi la contrôler et limiter la perte irréversible de capacité. Les performancesen capacité de l’élément lithium-ion sont directement liées à cette valeurde capacité irréversible, elle doit être limitée afin de maximiser la quantité d’ionslithium échangée entre l’électrode négative et l’électrode positive. La stabilité dela SEI conditionne ensuite le comportement en cyclage de l’électrode au cours dutemps.Dans ce mémoire de thèse, nous avons choisi de caractériser le comportement del’électrode de graphite en faisant varier la nature de l’électrolyte et la taille desparticules de graphite tout en restant le plus proche possible du fonctionnementd’une vraie batterie. Au travers des techniques de caractérisations électrochimiques(cyclage galvanostatique, spectroscopie d’impédance) associées à des techniques decaractérisation de surface (spectroscopie de photoélectrons X, microscopie électroniqueà balayage), les résultats obtenus ont permis de proposer un nouveau modèlede formation de la SEI.Pour l’électrolyte, nous avons choisi de ne regarder que l’effet du solvant (le carbonatede propylène) et de l’additif (le carbonate de vinylène). Ces deux composésentrent dans la composition des électrolytes utilisés dans les éléments lithium-ioncommerciaux. Pour l’électrode de graphite, le choix des particules s’avère primordialpuisque chaque type de particules possède une chimie de surface spécifique (plans223basaux ou plans prismatiques) susceptible de réagir différemment vis-à-vis de l’électrolyte.Deux particules de graphite, de taille et de morphologie différentes, ont étéétudiées. Elles sont utilisées séparément en tant que matière active dans les électrodesnégatives des batteries lithium-ion. Notre spécificité est d’avoir préparé desélectrodes constituées par un mélange de ces deux particules et de les avoir ensuitecaractérisées en formation. L’application de conditions de fonctionnement différentescomme le régime de cyclage et la température d’essai ont mis en évidence les valeursidéales conduisant à minimiser la dégradation de l’électrolyte et à optimiser laqualité du film.Nous avons abouti, au travers de l’ensemble des méthodes de caractérisations misesen oeuvre, à une meilleure compréhension des mécanismes de formation du film depassivation permettant ainsi d’améliorer cette étape essentielle à la pérennité desperformances de l’électrode dans le temps. Ce travail a donc un réel impact auniveau industriel. Le modèle de formation proposé apporte un éclairage nouveau auprocessus de formation et peut permettre également d’aider en amont à la fabricationdes particules de graphite. / This work relates to the lithium ion battery field. The purpose of this study is tobetter understand the behavior of graphite electrodes by focusing on the formationof a passive layer named Solid Electolyte Interface (SEI) which is formed at thegraphite/electrolyte interface. This work has led us to put forward models whichcan explain the SEI formation and identify the reactions which take place in alithium ion battery.The SEI results from reactions between graphite electrode, lithium ions and organicmolecules from the electrolyte during the first charge of the lithium ion battery. It ismainly composed of decomposition products from the electrolyte. Consumed lithiumions can no longer be used in the next cycle. The SEI is therefore responsible for theirreversible capacity during the first formation cycle which is the charge loss betweenthe intercalation process and the deintercalation process. It is necessary to betterunderstand the impact of the formation conditions and other parameters in orderto control and limit the irreversible charge loss. Lithium ion battery performancesdepend on this irreversible capacity, this value has to be reduced in order to maximizethe amount of exchanged lithium ions between negative and positive electrodes. TheSEI stability will determine the electrode behavior upon cycling.In this thesis, we chose to study the graphite behavior by testing several electrolytecompositions and graphite particle sizes in electrochemical cells similar to areal battery. Electrochemical techniques (galvanostatic cycling and electrochemicalimpedance spectroscopy) and surface analyses (X-ray photoelectron spectroscopy,scanning electron microscopy) will be combined. These results helped us to developa new model of the SEI formation.For the electrolyte, we chose to study the effect of the solvent (propylene carbonate)and the additive (vinylene carbonate). Both components are commonly used inthe electrolyte for commercial lithium ion batteries. For the graphite electrode, thechoice of graphite particles is essential because each graphite family has its ownsurface chemistry (basal and prismatic surfaces) which can react in many wayswith the electrolyte. Two graphite particles, with specific sizes and morphologiesare studied. They are separately used as active materials for negative electrodes inlithium ion batteries. Our unique approach is to prepare graphite electrodes basedon a mix of both particles with various compositions and then test the electrode225performances. After testing several formation conditions such as the cycling rateand the temperature, we found the ideal formation conditions for minimizing theelectrolyte decomposition and optimizing the film quality.Finally, based on all the characterization methods, we came to a better understandingof the film formation process. In this way, we have improved this essentialpreliminary step which can now lead to more durable cycling performances overtime. This study can have a major impact on the industrial level. The formationmodel cast a new light on the formation process and can therefore help to makeefficient graphite electrodes.