Nanotechnology enabled synthesis of various shapes and morphologies of conventional materials. Nanotubes, nanoparticles, quantum dots and nanowires are the new form of materials. Especially nanowires have gotten great attention due to their unique physical, chemical and optical properties. Superior properties of nanowires are based on their high surface area and two quantum confinement directions. Silver is one of the most conductive metals and it has the highest thermal conductivity. Due to excellent properties of bulk silver its nanostructures especially silver nanowires have been widely studied. Silver nanowires have been demonstrated to be used in optical polarizers, photonic crystals, surface enhanced Raman spectroscopy and recently transparent and conducting electodes. Hence, production of silver nanowires through a cost-effective and well controlled method could make important contributions to these and other unprecedented. So far, many different methods have been explored for the synthesis of silver nanowires. Vapor-liquid-solid (VLS) technique, hard template techniques such as porous anodic alumina synthesis and soft template techniques such as DNA based synthesis and polyol process are some silver nanowire synthesis methods. Among these methods, solution based polyol process is the most feasible one in terms of cost, yield and simplicity. In this thesis, polyol process, which is a novel and solution based method enabling the synthesis of silver nanowires with precise length and diameter control, is investigated. A detailed parametric study resulting in a full control over the resultant nanowire morphology is provided. The parameters affecting the structure have been determined as temperature, injection rate, poly(vinylpyrrolidone):silver nitrate (PVP:AgNO3) molar ratio, sodium chloride (NaCl) amount and stirring rate. The results show that polyol process method could replace the conventional silver nanowire fabrication methods. It was shown that specific nanowire lengths and diameters for any application can be obtained simply by adjusting the parameters of the process.

Drug discovery is reliant on new developments in natural product chemistry as well as advances in chemical synthesis. The interconnectivity and interdependence of natural and synthetic investigation in drug discovery is evident. The chemical exploration reported herein elaborates the relationship between natural product chemistry and chemical synthesis. Of particular interest are chemicals from organisms residing in less accessible environments, particularly Antarctica and endophytic microbial communities. Degradation via reductive ozonolysis of palmerolide A, a macrocyclic polyketide isolated from the Antarctic tunicate Synoicum adareanum, and subsequent synthetic preparation of the resulting polyols (1,2,6-hexanetriol and 1,2,3,6-hexanetetraol) led to a revision in the absolute configuration of the bioactive natural product (7R, 10R, 11R to 7S, 10S, 11S). A partial synthesis of palmerolide A (C3-14) was completed using Grubb’s 2nd generation catalyst to couple fragments formed using the previously developed methodology from the degradation study. Isolation of indole-pyrimidine containing alkaloids meridianins A, B, C, and E from the Antarctic tunicate Synoicum sp. prompted a synthetic investigation of psammopemmin A, a related alkaloid from the Antarctic sponge Psammopemma sp. resulting in reassignment of the structure of psammopemmin A to that of meridianin A. Both meridianin A and psammopemmin A were synthesized through a Suzuki coupling of the same 4-indolol nucleophile to the apposite pyrimidine electrophile. Several synthetic 3-pyrimidylindole analogs were also prepared and investigated for central nervous system, antimalarial, and cytotoxic activity. Chemical investigation of extracts from mangrove fungal endophytes that displayed antimalarial properties in vitro resulted in the isolation of several potent but cytotoxic and cytostatic compounds: cytochalasin D, roridin E, and 12,13-deoxyroridin E.

O grafeno, material com duas dimensões (2D), formado por átomos de carbono hibridizados em sp2, tem atraído muita atenção da comunidade científica devido às propriedades elétricas, térmicas e mecânicas excepcionais que este material apresenta. Nanopartículas (NPs) de metais e de óxidos metálicos têm sido incorporadas sobre a estrutura do grafeno com o objetivo de obter materiais compósitos. Este trabalho teve por objetivo principal desenvolver uma nova rota para a preparação de compósitos de grafeno/NPs metálicas e de óxidos metálicos pelo método do poliol modificado, em etapa única. O óxido de grafeno (GO) foi sintetizado pelo método Hummers modificado e reduzido e esfoliado pelo processo pioliol modificado para obtenção do grafeno. Ajustou-se a metodologia proposta para que o GO obtido pudesse ser utilizado diretamente no meio reacional do processo poliol sem a necessidade de secagem e redispersão. Foram testadas diversas condições de síntese do grafeno variando-se a presença e tipo de surfactante, o solvente e diferentes condições de aquecimento. As variações de síntese permitiram observar que a presença do surfactante oleilamina aumenta a capacidade redutora do sistema e inibe a formação de outras estruturas de carbono além do grafeno e taxas de aquecimento menores favorecem a formação de grafeno em detrimento destas outras estruturas, enquanto patamares de temperatura intermediários levam à formação dessas estruturas secundárias de carbono. As sínteses foram também adaptadas para a obtenção de compósitos de grafeno/NPs de FePt e Fe3O4. Estas sínteses foram realizadas de duas maneiras: com os precursores metálicos e o GO presentes no balão desde o início da síntese e com os precursores metálicos presentes no balão desde o início da síntese e hot injection do GO. Para os compósitos, as sínteses realizadas em benzil éter (BE) favoreceram a formação de partículas. Para os compósitos de grafeno/NPs de Fe3O4, observou-se que a quantidade de precursor de Fe é crucial para a formação das NPs. Os resultados indicaram que a metodologia empregada foi muito eficiente para produção de grafeno e de compósitos de grafeno/NPs em etapa única e o processo poliol se mostrou muito versátil, de maneira que os resultados obtidos indicam que é possível obter compósitos de grafeno com qualquer sistema de NPs que venham a ser sintetizadas pelo processo poliol, apenas pelo ajuste das condições de síntese, em etapa única. / Graphene, a two dimensional material, composed only by sp2 hybridized carbon atoms, have attracted much attention of the scientific comunity due to the exceptional electrical, thermal and mechanical properties this material presents. Metallic and metal oxide nanoparticles (NPs) have been incorporated over graphene structure in order to obtain composite materials. The main goal of this work was to develop a new synthetic route to obtain graphene and metallic and metal oxide NPs composites, in one step. Graphene oxide (GO) was sinthesized by the modified Hummers method and exfoliated and reduced by the modified polyol process to obtain graphene. The proposed methodology was adjusted for the obtained GO to be used directly in the polyol process reactional means, not being necessary to dry and to redisperse the material. Several synthesis conditions were tested to obtain graphene, varying the presence of the surfactant and its type, solvent and heating rates. The synthesis diversity let us observe that the presence of oleylamine improved the reducing capacity of the system and it inhibited other carbon structures formation besides graphene. Also, smaller heating rates favor graphene formation to the detriment of these other structures, whereas intermediate temperature plateaus lead to the formation of carbon secondary structures. The synthesis were also adapted in order to obtain graphene/NPs of FePt and Fe3O4 composites. These synthesis were performed in two ways: both metallic precursors and GO present in the flask since the begining of the synthesys and only methalic precursors present in the flask since the begining of the synthsys, with a GO hot injection. Regarding the composites, synthesis performed in benzyl ether (BE) favor the particles formation. And specifically on the graphene/NPs of Fe3O4 composites, it was observed that Fe precursor quantity is decisive on the NPs formation. The results indicated that the employed methodology was very efficient to produce graphene and graphene/NPs composites in one step. And the polyol process proved to be very versatile, thereby the obtained results indicate it\'s possible to obtain graphene/NPs composites, in one step, with any NPs system that can be synthesized by the polyol process, only by adjusting the synthesis condition.

Philosophiae Doctor - PhD / Direct methanol fuel cells (DMFCs) are attractive power sources as they offer high conversion efficiencies with low or no pollution. One of the major advantages DMFCs has over PEMFCs is that methanol is a liquid and can be easily stored where in the case for PEMFCs storing hydrogen requires high pressures and low temperatures. However, several challenging factors especially the sluggish oxygen reduction reaction (ORR) and the high cost of Pt catalysts, prolong their commercialization. With the aim to search for more active, less expensive more active ORR catalysts and methanol tolerant catalysts than pure Pt, this dissertation focuses on the development of low loading Pt electrocatalyst and the understanding of their physical and electrochemical properties. Pt-Sn/C electrocatalsyts have been synthesized by a modified polyol reduction method. The effect of temperature, pH, water, sonication and addition of carbon form were studied before a standard polyol method was established. From XRD patterns, the Pt-Sn/C peaks shifted slightly to lower 2Ө angles when compared with commercial Pt/C catalyst, suggesting that Sn is alloying with Pt. Based on HRTEM data, the Pt-Sn/C nanoparticles showed small particle sizes well-dispersed onto the carbon support with a narrow particle distribution. The particle sizes of the different as-prepared catalysts were found to be between 2-5 nm. The Pt-Sn/C HA Slurry pH3 catalysts was found to be the best asprepared catalyst and was subjected to heat-treatment in a reducing atmosphere at 250-600 °C which led to agglomeration yielding nanoparticles of between 5-10 nm. The Methanol Oxidation Reaction (MOR) on the as-prepared Pt-Sn/C HA Slurry pH3 catalyst appeared at lower currents (+7.11 mA at 860 mV vs. NHE) compared to the commercial Pt/C (+8.25 mA at +860 mV vs. NHE) suggesting that the Pt-Sn/C catalyst has „methanol tolerance capabilities‟. Pt-Sn/C HA Slurry pH3 and Pt-Sn/C 250 °C catalysts showed better activity towards the ORR than commercial Pt/C with specific and mass activities higher than Pt/C at +0.85 V vs NHE. The Tafel slopes of Pt-Sn/C HA Slurry pH3 catalyst was -62 and -122 mV dec-1 for the low and high current regions respectively and suggests that the ORR mechanism is similar to that of commercial Pt/C indicating that the ORR kinetics was not negatively influenced by the addition of tin. It was found that the electrochemical oxidation reduction reaction follows first order kinetics of a multi-electronic (n=4ē) charge transfer process producing water. All the Pt-Sn/C catalysts showed resistance towards MOR and it was found for the heat-treated catalysts that an increase in temperature resulted in an increase in methanol tolerance. The synthesized Pt-Sn/C HA Slurry pH3 catalysts were also tested in a fuel cell environment. Electrodes were prepared by either spraying on Toray carbon paper with the Asymtek machine or by VI spraying directly on the membrane with a hand spray gun the catalysts coated membrane (CCM) technique. Polarization curves obtained in DMFC with CCM showed superior performance than electrode prepared by spraying on the carbon paper with the machine. In our study, the Pt-Sn/C catalyst appears to be a promising methanol tolerant catalyst with activity towards the ORR in the DMFC.

L’étude de ce mémoire concerne l’élaboration d'un alliage alternatif sans plomb pour l’électronique de puissance, celui-ci sera utilisé à des fins de brasures. Les brasures actuelles sont composées d’alliages comportant du plombet sont peu résistantes en cas de travail à haute température. Ces systèmes seront progressivement éliminés, ils ne respectent plus la Directive Européenne sur l’environnement (RoHS) et les normes de santé publique en raison de la toxicité du plomb (cancérogène, mutagène, accumulation dans l’environnement …). Le travail a été réalisé avec l’alliage Ag-Sn, l’objectif principal de cette thèse a été d’élaborer le composé Ag3Sn, en raison de sa grande résistance thermique (température de fusion élevée de 480°C). Ses meilleures performances sont avantageuses pour les brasures situées dans des environnements difficiles comme l’aéronautique ou l’automobile. La première partie de ce manuscrit détaille la synthèse du composé Ag3Sn réalisée via la méthode polyol, une voie de chimie douce. Il s’agit d’une technique différente des techniques classiques, comme la voie métallurgique. La synthèse a été réalisée en plusieurs étapes et une méthode d’approches successives a été utilisée afin de déterminer les paramètres de synthèse optimums.Deux protocoles particuliers se détachent et ils permettent d’élaborer des phases résistantes à haute température. Lepremier permet d’élaborer une phase pure d' Ag3Sn, tandis que le second permet d’élaborer deux phases de solutionssolides. Les composés ont été caractérisés par DRX, par imagerie MEB-FEG et MET et par analyse thermogravimétrique.La seconde partie de ce travail est la consolidation de ce composé Ag3Sn par une technique de frittage particulière :le die-bonding, afin de réaliser la connexion entre la puce électronique et un susbtrat de cuivre recouvert d'argent.Une étape de dépôt des poudres sur le substrat a été nécessaire avant de réaliser la consolidation, elle a été réalisée selon différentes techniques : le spin-coating ou le dépôt par sérigraphie. Puis, les paramètres de frittage par die-bonding ont été affinés selon les techniques de dépôt. Enfin, des essais de cisaillement ont été réalisés sur certains échantillons. / The study of this memoir concerns the development of an alternative lead-free alloy for power electronics, which will be used for solders. Nowadays, current solders are composed of alloys containing lead, and aren't resistant at high work temperature. These systems will be phased out, because they no longer comply with the European RoHS Directive and public health standards due to the toxicity of lead (carcinogenic, mutagenic, accumulation in the environment, etc.). This work was carried out with the Ag-Sn alloy, and the main objective was to develop the elaboration of the Ag3Sn compound, due to its high thermal resistance (high melting point of 480°C). Its best performance is an advantage for solders located in difficult work environments such as aeronautics or automobile. First part of this thesis describes the synthesis of Ag3Sn compound with the polyol process, a soft-chemistry routine. It is different from the conventional techniques, like the metallurgical way. Polyol synthesis was realized by following several steps. A method of successive approaches wasdetermine optimum synthesis parameters. Two specific protocols stand out, and they allow the development of high-temperature resistant phases. The first one allows the elaboration of an Ag3Sn pure phase, an the second one allows the development of two compounds of solid solutions. The compounds were characterized by XRD, FEG-SEM, TEM and thermogravimetric analysis. The second part of this work is the consolidation of the Ag3Sn compound with a special sintering technique : the die-bonding, in order to realize the connexion between the electronic chip and the copper substrate coated silver. A first step of depositing powder on the substrate was necessary before carrying out the implementation. It was carried out with various techniques : spin-coating orthe serigraphy deposition. Then, sintering parameters were refined according to the deposition techniques. Finally, shear tests were performed on different samples

La demande en composés chiraux est en plein essor ces dernières années. Pour accéder à leur synthèse, la biocatalyse, couplée à l’irradiation pourrait être une méthode innovante. Il existe en effet de nombreux cas dans la littérature où l’utilisation de micro-onde semble avoir un effet activateur sur l’efficacité enzymatique.Cependant, l’effet de l’irradiation micro-onde est mal compris et controversé. Le but de cette thèse était d’étudier l’impact de l’irradiation micro-onde sur des lipases, immobilisées ou non, en étudiant différentes réactions modèles, allant de la résolution d’alcools secondaires linéaires simples à la résolution de polyols complexes, et alcools polyfonctionalisés, par comparaison entre chauffage sous irradiation micro-onde (en conditions drastiques ou non) au chauffage classique. L’étude de l’irradiation micro-onde sur la stabilité enzymatique et sur paramètres intrinsèques de l’enzyme après modification des paramètres réactionnels a permis de mettre en évidence un rôle indéniable de l’irradiation micro-onde sur l’efficacité des réactions enzymatiques. Il a été possible d’une part de diminuer de façon importante les temps réactionnels, comparé au chauffage traditionnel,et d’autre part de contrôler efficacement l’énantio préférence et la sélectivité de la lipase pour l’obtention de molécules d’intérêt. Par des procédés innovants, l’impact de la puissance d’irradiation a été montré comme hautement dépendant du modèle réactionnel étudié. En optimisant les conditions réactionnelles pour obtenir les meilleures sélectivités et activités enzymatique sous irradiation micro-onde, la synthèse de a-hydroxyamides chiraux et de polyols parfaitement résolus a pu être entreprise de façon rapide, propre, tout en respectant les principes de chimie verte. / Chiral molecules demand is booming in recent years. Biocatalyse under microwave irradiation is found to be an attractive way to synthesise these molecules. Indeed, in the literature, some cases show an activation effect on the enzymatic efficiency by microwave irradiation, compared to classical heating. However, the effect of microwave irradiation is not well understood and controversial. The aim of his PhD was to study the impact of the microwave irradiation on some lipases, immobilized or not. Different model reactions were studied from secondary linear alcohol resolution, to the resolution of more complex polyols or polyfunctionalized secondary alcohols comparing the microwave heating (in drastic conditions or not) to the classical heating. Studying the enzymatic stability and intrinsic parameters after modifying the reaction parameters, we observed a clearly microwave effect on the efficiency of the enzymatic resolutions. Using microwave heating, it could be possible to decrease, in an important way, the reaction time, compared to the classical heating and to control the énantiopréférence of the lipase to efficiently obtain chiral product. Trough innovative processes, the impact of the irradiation has been studied and it depends on the model reaction.Optimizing the conditions to obtain the best enzyme selectivities and activities under microwave irradiation, we could synthesise chiral a-hydroxyamides and polyols, in a rapid, clean way, respecting the principles of green chemistry.

Le marché des dispositifs optoélectroniques (écrans, capteurs tactiles, cellules solaires…) transparents flexibles est en pleine expansion. Traditionnellement l’oxyde d’indium-étain (ITO) est utilisé comme électrode transparente, mais son importante fragilité mécanique couplée à une disponibilité future incertaine de l’indium (matériau classé comme critique par la commission européenne) nécessite de trouver des alternatives. Les nanofils métalliques, notamment à base d’argent, font partie des développements les plus avancés avec des performances optoélectroniques excellentes, ainsi qu’une mise en œuvre simple et des techniques d’impression bas coût compatibles avec les substrats flexibles. A l’aube d’une utilisation massive probable de ce nanomatériau, des questionnements émergent quant à leur toxicité potentielle, notamment en raison de leur facteur de forme rappelant celui de l’amiante. Ces travaux de thèse se déclinent selon trois axes : synthèse, propriétés et toxicité. L’optimisation du procédé polyol pour la synthèse des nanofils d’argent a conduit au contrôle indépendant des dimensions (diamètre et longueur). La détermination des performances optoélectroniques a permis un adressage précis des performances visées, en identifiant les morphologies adaptées à chaque domaine d’application. Le contact cutané et l’inhalation ayant été identifiés comme les principales voies d’exposition des nanofils d’argent durant leur mise en œuvre, des études de toxicité sur des fibroblastes et macrophages ont été réalisées. Ceci a permis l’identification de mécanismes biologiques différents selon la morphologie des nanofils mais également selon le type cellulaire. Ces nanofils apparaissent peu toxiques, notamment en comparaison à d’autres nanomatériaux connus. Cette approche dite « safer by design » permet in fine d’orienter la sélection des meilleurs nanofils en fonction de l’application ciblée. / The market for flexible transparent optoelectronic devices (displays, touch screens, solar cells, etc.) is expanding rapidly. Traditionally indium tin oxide (ITO) is used as a transparent conductive layer material, but its high mechanical fragility coupled with an uncertain future availability of indium (material classified as critical by the European Commission) requires alternatives material to be found. Metal nanowires, especially silver-based, are among the most advanced developments with excellent optoelectronic performances, as well as simple processing and printing techniques compatible with flexible substrates. At the dawn of a probable massive use of this nanomaterial, questions are emerging regarding to their potential toxicity, in particular because of their shape factor reminiscent of that of asbestos. This thesis is based on three axes: synthesis, properties and toxicity. The optimization of the polyol process for the synthesis of silver nanowires led to the independent control of dimensions (diameter and length). The determination of the optoelectronic performances allowed to determine the targeted performances, by identifying the morphologies adapted to each field of application. Since dermal contact and inhalation were identified as the main routes of exposure for silver nanowires during their implementation, toxicity studies on fibroblasts and macrophages were conducted. This allowed the identification of different biological mechanisms according to nanowire morphology but also according to cell type. These nanowires appear to have a low toxicity, especially when compared to other known nanomaterials. This "safer by design" approach makes possible to orient the selection of the safer nanowires according to the required performances of targeted application.

Les électrodes transparentes sont les composants indispensables de nombreux dispositifsoptoélectroniques commerciaux (cellules solaires, écrans plats, écrans tactiles ou encorediodes électroluminescentes). Elles sont constituées le plus souvent d’oxyde d’indium etd'étain (ITO). Les électrodes à base d'ITO sont produites par un procédé relativementcoûteux et sont très fragiles à la contrainte mécanique, ce qui limite leur utilisation au seinde dispositifs optoélectroniques flexibles. Des matériaux alternatifs, sans indium, à base deréseaux de nano-fils d’argent, font actuellement l'objet d'un grand nombre de recherches.Ces réseaux à base de nanostructures métalliques ont des propriétés opto-électroniquescomparables voire supérieures à celles de l’ITO. Ils sont adaptables à des substrats flexibleset sont compatibles avec les procédés de dépôt « roll to roll ». L'objectif de cette thèse estd'explorer de nouvelles voies de synthèse et de modification de surface de nanofils d'argentpour développer des électrodes transparentes plus performantes. De nouvelles nanostructuresmétalliques, différentes de celles commercialisées, ont été élaborées : (i) des fils d’argentultra-longs (ii) des fils d’argent présentant une architecture inhabituelle i.e avec desramifications. Des paramètres clés du procédé polyol ont été modifiés pour élaborer les filsà facteur de forme très élevé. Ils ont permis d'accroître les performancesrésistance/transparence des dispositifs conventionnels. Des nano-fils d’argent de forme « Y» ou « V » ont également été synthétisés en soumettant le milieu de croissance à des ultrasons.Ces nanostructures devraient permettre de limiter les problèmes de conduction quiapparaissent, à l'heure actuelle, au niveau des contacts entre les fils dans les dispositifsnanostructurés. Par ailleurs, des réseaux de fils d'argent modifiés en surface avec de l'acide11-mercaptoundecanoïque (MuA) ont été élaborés. Ils constituent une solution trèsintéressante pour améliorer la stabilité chimique des réseaux métalliques. Le MuA limite l'oxydation de surface du métal et permet aux électrodes de conserver leurs transparence etconductivité initiales. / Transparent electrodes are a necessary component in a number of devices such as solar cells,flat panel displays, touch screens and light emitting diodes. The most commonly usedtransparent conductor, indium tin oxide (ITO), is expensive and brittle, the latter propertymaking it inappropriate for up-and-coming flexible devices. Films consisting of randomnetworks of solution-synthesized silver nanowires have emerged as a promising alternative toITO. They have transparency and conductivity values better than competing new technologies(e.g. carbon nanotubes films, graphene, conductive polymers, etc.) and comparable to ITO.Furthermore, these silver nanowire films are cheap, flexible, and compatible with roll-to-rolldeposition techniques. The main objectives of this PhD work are to improve the properties ofsilver nanowire electrodes and to study and solve issues that are currently hindering their usein commercial devices. Specifically, I studied the important areas of electrode conductivity andstability. To increase the conductivity of nanowire electrodes, two silver nanostructuresdifferent from what is commercially available were synthesized i) ultra-long nanowires and (ii)branched nanowires. Regarding (i), by using 1.2-propanediol as the medium rather than thetypical ethylene glycol in the polyol synthesis process, as well as the molecular weight of PVP,the temperature of the process, or the concentration of silver nitrate, we obtained silvernanowires with an aspect ratio between their lengths and diameters of 1050. Among all theultra-long silver nanowires elaborated in polyol process reported in the literature, they have themaximum length. The synthesis developed is also cheap and the reaction time takes less than2h. Moreover, they have a high yield of 2 mg/ml. Electrodes with a sheet resistance of 5 Ω/Sqfor a transparency of 94% were obtained (with post thermal treatment applied). However, thispost-deposition anneal is shown to have a small influence on the decrease of the sheetresistance. It is thus not required to elaborate electrodes with good performance, which is veryadvantageous for the elaboration of electrodes on plastic substrates. Regarding (ii), “V-like shape” or “Y-like branched” nanowires were elaborated thanks to the input of ultrasonicirradiation during the polyol process. Unfortunately, their length being short (6 μm), theirinterest is limited to enhance the performance of transparent electrodes. In addition, structuralanalyses of both branched and unbranched nanowires revealed the nanostructures notmonocrystalline. Concerning the stabilities issues, the thermal stability of silver nanowireelectrodes coated with graphene was investigated. This coating allows a better homogeneity ofthe heat through the network, decreasing the number of hot spots and thus increasing thelifetime of the electrodes. The corrosion of silver nanowire and the resulting electrode resistanceincrease over time is a severe problem hindering their use in commercial devices. 11-mercaptoundecanoic acid (MuA) was identified as a promising passivation agent of silvernanowires. Lifetime testing showed that the electrode resistance increased more slowly (12%)than any other passivated electrodes reported in the literature. Furthermore, unlike many otherpassivation methods, the MuA molecule itself does not negatively affect the conductivity ortransparency of the electrode and is very inexpensive, all contributing to the commercialviability of the passivation method.

L'étude du mécanisme de la réaction d'oxydation de l'éthanol (EOR) a été réalisée sur des électrocatalyseurs bi- et tri-métalliques à base de Pt, Rh et SnO2 sur support carboné à l'aide de méthodes électrochimiques couplées (DEMS, in situ FTIR). Deux importantes problématiques de l'EOR ont été abordées: la déshydrogénation de la molécule d'éthanol et la cassure de sa liaison C-C.L'investigation de certains paramètres expérimentaux, comme l'épaisseur de la couche d'électrocatalyseur, a permis de démontrer q'une couche active épaisse conduit à une meilleure électrooxydation plus complète de l'éthanol en CO2, mais également que l'empoisonnement de l'électrocatalyseur par de très forts adsorbats advient dans l'épaisseur de couche active.Les performances de chaque électrocatalyseur ont été comparées entre elles et ont mis en évidence une meilleure sélectivité de l'EOR sur Pt-Rh-SnO2/C, ainsi que l'engendrement de courants plus élevés à bas potentiel à température ambiante. La tendance est amplifiée à température plus élevée (T = 60 °C). / The study of the ethanol oxidation reaction (EOR) mechanism was performed on carbon supported bi- and tri-metallic Pt-, Rh-, SnO2-based electrocatalysts via electrochemical coupled techniques (DEMS, in situ FTIR). Two of the most important issues related to the EOR have been broached: the dehydrogenation of the ethanol molecule and its C-C bond breaking.The investigation of some experimental parameters, such as the thickness of the electrocatalyst layer, enabled demonstrating the better complete ethanol electrooxidation into CO2 for large electrocatalysts layers, combined to the enhanced poisoning effect inside the catalyst layer by very strong adsorbates.The performances of each electrocatalyst were compared and evidenced an improved selectivity of the EOR on Pt-Rh-SnO2/C, as well as the generation of higher currents at low potential at room temperature. The tendency was amplified at elevated temperatures (T = 60 °C).

L’objectif principal de ce travail est de produire des pièces massives nanostructurées à partir des nanomatériauxd’alliages anisotropes à base des éléments de transition 3d (Co et Ni). Afin d’utiliser ces nanomatériaux àl’échelle industrielle, nous avons extrapolé la méthode de synthèse de l’échelle du laboratoire (procédé polyol) àl’échelle pilote. Tout d’abord, nous avons montré qu’en variant les paramètres de synthèse à l’échelle delaboratoire, nous pouvons contrôler non seulement la morphologie mais aussi la taille et la distribution de tailledes nanoparticules. En effet, des sphères de diamètre 10 nm et des nanofils de longueur 260 nm et de diamètre 7nm ont été obtenus pour la stoechiométrie Co80Ni20. Les paramètres clés de cette étude sont la concentration dela soude, le taux de l'agent nucléant, la vitesse d’agitation et le champ magnétique externe appliqué. Le choix dusystème de mélange approprié pour une géométrie du réacteur donnée a également un rôle important dans lecontrôle et la maîtrise de la taille et la forme des nanofils. Avec une turbine Rushton à six pâles droites, nousavons obtenu des nanofils plus courts avec de plus petites têtes coniques et une forte coercitivité. Par ailleurs, larésolution numérique des équations de Navier-Stocks qui gouvernent le transport de matière et de la quantité demouvement dans un fluide agité a permis d’obtenir une corrélation entre les profils d’énergie turbulente dissipéeet la taille des nanoparticules mesurée expérimentalement. Les études magnétiques montrent que les propriétésmagnétiques des nanofils sont intimement liées à leur forme et à leur taille. La synthèse à grande échelle apermis de produire 25 grammes de nanofils de cobalt-nickel par batch. Grâce au procédé de frittage SPS, nousavons élaboré avec succès des matériaux massifs nanostructurés à partir de la poudre formée des nanofils. Alorsque les nanofils présentent des champs coercitifs élevés et des aimantations relativement faibles, les matériauxdenses consolidés par SPS possèdent les caractéristiques d’un ferromagnétisme doux (faible champ coercitif)mais une aimantation à saturation élevée proche de celle attendue. Des champs coercitifs meilleurs sont obtenusavec le matériau dense nanostructuré élaboré en présence d’un champ magnétique permanent. Ce champmagnétique a permis un meilleur alignement des nanofils au cours du frittage. Le comportement mécanique desmatériaux nanostructurés dépend essentiellement de la taille des grains. La dureté et la résistance mécaniqueaugmentent quand la taille des grains diminue conformément à la relation de Hall-Petch. / The main objective of this PhD work is to produce nanostructured bulk from anisotropic nanomaterials alloysbased on 3d transition elements (Co and Ni). For using these nanomaterials on an industrial scale, we haveextrapolated the synthesis method (polyol process) from laboratory scale to pilot scale. First, we showed that byvarying the parameters synthesis in laboratory scale we can control not only the morphology but also the size andthe size distribution of the nanoparticles. Indeed, spheres with diameter of 10 nm and nanowires with meanlength of 260 nm and a diameter of 7 nm were obtained for a stoichiometry Co80Ni20. The key parameters of thissynthesis are the concentration of the sodium hydroxide, the nucleation rate, the agitation and the appliedexternal magnetic field. The choice of suitable mixing system for a given geometry of the reactor also has animportant role for the control of the size and shape of the nanowires. When a six-bladed Rushton turbine wasused, shorter nanowires with unconventional small conical-shaped heads and a higher coercive field wereobtained, confirming a strong relationship between flow patterns and nanowire growth. Moreover, numericalresolution of Navier-Stocks equations that govern the transport of matter and quantity of movement in anagitated fluid allowed us to obtain a correlation between turbulent energy dissipation profiles and nanoparticlesize measured experimentally. Magnetic studies revealed a narrow relationship between the magnetic propertiesand the shape of nano-objects. The large-scale synthesis has produced 25 grams of cobalt-nickel nanowires perbatch. Thanks to the SPS sintering process, we have successfully elaborated nanostructured bulk materials.Whereas nanofils show high coercive field and low saturation magnetization, dense materials produced at hightemperatures behave as soft ferromagnetic materials (low coercivity) but show high saturation magnetizationvery close to that expected. The best coercivities are obtained with the bulk nanostructured material using SPSassisted by a permanent magnetic field. This magnetic field succeeded to align the nanowires during sintering.The mechanical behavior of the nanostructured materials depends mainly on the grain size. Hardness andmechanical resistance increase when the grain size decreases in agreement with the Hall-Petch relationship.