Les travaux de recherche actuels menés dans le domaine des supercondensateurs s’orientent vers l’augmentation des densités d’énergie, notamment via le développement de supercondensateurs hybrides "oxydes de métaux de transition / carbones activés". Dans ce contexte, les présents travaux avaient pour objectif d’évaluer les propriétés d’oxydes de cobalt nanométriques en tant que matériaux d’électrode positive pour supercondensateur hybride.Ces oxydes de cobalt, de structure spinelle, sont préparés par précipitation de nitrate de cobalt en milieu basique (T < 90 °C). Ils possèdent une formule chimique du type HxLiyCo3-δO4•zH2O et présentent une bonne conductivité électronique grâce à la présence d’ions H+, Li+ et Co4+. Les analyses par DRX, ATG, RMN et les mesures de conductivité électroniques ont mis en évidence une réorganisation de la structure spinelle de ces matériaux sous l’effet d’un traitement thermique, conduisant à une augmentation du rapport Co4+/Co3+ ainsi qu’à une amélioration des propriétés de transport électrique. L’association d’une conductivité électronique élevée et d’une forte surface spécifique confère à ces oxydes des performances prometteuses en tant que matériaux d’électrode.L’étude des propriétés électrochimiques a montré la présence de deux modes de stockage des charges, l’un électrostatique (double couche électrochimique) et l’autre faradique via l’oxydation et la réduction du cobalt. Elle a également permis de déterminer la signature électrochimique de ces oxydes (capacité, fenêtre de potentiels), prérequis indispensable à leur intégration dans une cellule complète. Finalement, un supercondensateur hybride "oxyde de cobalt / carbone activé" a été assemblé et équilibré, donnant lieu à des performances attractives (61,6 F/g sur 1,60 V). / Investigations on supercapacitors are focusing on increasing energy densities, in particular with the development of hybrid supercapacitors "metal oxides / activated carbons". In this field, the present work aims at evaluating nanometric cobalt oxides as positive electrode material for hybrid supercapacitors.These oxides, with spinel structure, are synthesized by precipitation of cobalt nitrate in a basic medium (T < 90 °C). They exhibit formulae such as HxLiyCo3-δO4•zH2O and good electronic properties thanks to the presence of H+, Li+ and Co4+ ions. XRD, TGA, NMR analysis as well as electronic measurements have highlighted a structural reorganization of the spinel structure under thermal treatment, resulting in increase of the Co4+/Co3+ ratio and an enhancement of the electronic transport properties. The high electronic conductivity together with a huge specific surface area imparts these oxides promising performances as electrode material.The study of the electrochemical properties underlines two charge storage mechanisms, one electrostatic (electrochemical double layer) and the other one faradic through the oxidation and the reduction of cobalt. The electrochemical signature (capacity, potential window) of these oxides was also determined in order to develop a complete cell. Finally, a hybrid supercapacitor "cobalt oxide / activated carbon" was assembled and balanced, revealing attractive performances (61,6 F/g over 1,60 V).

Actuellement, les supercondensateurs sont au centre de beaucoup de recherches. Ils offrent une solution potentielle pour le stockage réversible de l´énergie que ce soit pour le domaine spatial, aéronautique ou encore le transport (véhicules hybrides). Un axe de recherche important, visant à augmenter les densités d'énergie et de puissance, est consacré aux systèmes oxydes de métaux de transition /charbon actif (C) asymétriques. Les systèmes à base de RuO2 présentent les capacités les plus élevées, supérieures à 700 F/g, mais leur coût et leur toxicité limitent leur application aux petits appareils électroniques. Des oxydes moins coûteux tels que les oxydes de cobalt (notamment Co3O4), MnO2, V2O5, Fe3O4, NiO, Ni(OH)2, ainsi que des polymères conducteurs électroniques, ont été étudiés de manière approfondie au cours des dernières décennies jusqu’à être utilisés, pour certains, dans des dispositifs commerciaux. Mais aucun système n’a été aussi étudié que le C / MnO2. En effet, il a été démontré que ce dernier est particulièrement intéressant car il peut fonctionner dans des milieux aqueux à des tensions pouvant aller jusqu’à 2V tout en gardant une bonne stabilité électrochimique durant le vieillissement. Néanmoins, les performances du système, en particulier en termes de densité de puissance, sont limitées à cause de la mauvaise conductivité électronique du MnO2. Il est possible de surmonter ce problème en ajoutant à l’oxyde de manganèse, des matériaux conducteurs à base de carbone (noir de carbone, nanotubes de carbone…) ou encore, en développant des stratégies de greffage ou de décoration plus élaborées. La combinaison d’oxydes avec des espèces carbonées est très largement rapportée dans la littérature alors que le mélange d’oxydes de différente nature l’est beaucoup moins. Nous proposons dans ce projet de synthétiser et de développer des matériaux originaux améliorant, par un effet synergique, les propriétés intéressantes du manganèse, du cobalt et de l'oxyde / hydroxyde de nickel. Les inconvénients de chaque composant étant compensés par les bonnes propriétés complémentaires des autres. Nous cherchons à réunir en un seul matériau (ou composite), le bon comportement pseudocapacitif du manganèse, la bonne conductivité électronique associée aux oxydes de cobalt, la grande capacité de l'hydroxyde de nickel ainsi que les propriétés de conduction du carbone. Ce projet de doctorat vise à concevoir et à fabriquer de nouvelles classes d'électrodes composites hybrides basées sur des assemblages de graphène (pour la capacitance renforcée à double couche) et d'oxydes poreux de métaux de transition (pour une capacité faradique supplémentaire due à de multiples processus rédox réversibles). Les avantages combinés du graphène et des oxydes de métaux de transition permettront aux supercondensateurs à haute densité d'énergie de travailler dans des électrolytes aqueux respectueux de l'environnement ce qui est, aujourd’hui, un besoin reconnu. / Supercapacitors are the focus of much research at the present time. They offer a potential solution for reversible energy storage in the fields of space, aircrafts or transportation (hybrid vehicles). An important research line, aiming at increasing both energy and power densities, is devoted to asymmetric transition metal oxides / activated carbon (C) systems. RuO2-based devices exhibit the highest capacitance, more than 700 F/g, but their cost limits the applications to small electronic devices. Less expensive oxides such as cobalt oxides (especially Co3O4), MnO2, V2O5, Fe3O4, NiO, Ni(OH)2, as well as electrically conducting polymers, have been extensively studied in the past decades, or used in commercial devices; they EACH exhibit each drawbacks and advantages with regard to applications. But no system has been investigated as much as the C/MnO2 one, which is particularly interesting because it can work in aqueous media at tensions up to 2 V, and high stability in ageing has been demonstrated. Nevertheless, the performances of the system, especially in terms of power density, are limited by the poor electronic conductivity of MnO2. This problem is usually solved by simply mixing conductive carbon materials (carbon black, CNTs…) with MnO2 or by developing more elaborated grafting or decoration strategies. The combination of oxide and carbonaceous species is widely reported in the literature, whereas combining oxides with different natures is less frequently encountered. We propose in this project to synthesize and develop original materials enhancing, through a synergistic effect, the interesting properties of manganese, cobalt and nickel oxide/hydroxide, the drawbacks of each component being overbalanced by the good complementary properties of the other components. We aim at gathering in one single material (or composite), the good pseudocapacitive behavior of manganese, the good electronic conductivity associated to cobalt oxides, the high capacity of nickel hydroxide, as well as the enhanced conduction properties of carbon. The present PhD project aims at designing and manufacturing new classes of hybrid composite electrodes based on assemblies of graphene (for enhanced double layer capacitance) and porous transition metals oxides (for additional faradaic capacitance due to multiple reversible redox processes) directly applied on metallic current collectors. The combined advantages of graphene with those of transition metals oxides will enable supercapacitors with high energy density, working in environmentally friendly aqueous electrolytes, which are an acknowledged need. / A procura crescente de energia em setores distintos, como residencial, transporte e industrial, bem como a proliferação de fontes renováveis de produção de energia, exigem novos e mais eficientes dispositivos de armazenamento de energia. Consequentemente, tem-se observado um interesse crescente na produção e engenharia de materiais para armazenamento de energia. Muito dos esforços de R&D estão centrados no desenvolvimento de materiais nanoestruturados que possam responder aos requisitos da aplicação, tais como densidade de energia, densidade de potência e estabilidade face à ciclagem do dispositivo. Presentemente são muitos os materiais investigados como potenciais candidatos para elétrodos para dispositivos de armazenamento de energia por via eletroquímia, nomeadamente baterias, condensadores, pseudocondensadores ou supercondensadores. O objetivo do presente trabalho é produzir e estudar novos materiais com uma resposta eletroquímica intermédia entre um elétrodo típico de supercondensador e um elétrodo típico de bateria, também conhecidos como elétrodos híbridos. Por essa razão, selecionaram-se hidróxidos e óxidos de níquel e cobalto devido à sua elevada atividade eletroquímica e baixo custo. Estes materiais foram combinados com derivados de grafeno, que exibem alta condutividade e elevada área superficial ativa. Portanto, este trabalho foca a síntese e caracterização fisico química e eletroquímica de hidróxidos e óxidos de níquel-cobalto nanoestruturados e sua combinação com óxido de grafeno reduzido para aplicações de armazenamento de energia. A síntese foi efectuada por duas vias distintas: eletrodeposição e exfoliação. A eletrodeposição é usada para obter hidróxidos e óxidos de níquel-cobalto em combinação com óxido de grafeno reduzido. Os resultados evidenciam um efeito sinérgico quando o óxido de grafeno reduzido é combinado com o (hidr)óxido de níquel- cobalto, isto é, um aumento na capacidade, condutividade e estabilidade do compósito quando comparado com o (hidr)óxido de níquel-cobalto. Neste trabalho é dada especial atenção à espectroscopia de impedância eletroquímica que foi utilizada para avaliar os fenômenos que ocorrem durante a carga e descarga contínua e compreender os processos que ocorrem no material ativo e que resultam na sua degradação. O hidróxido de níquel-cobalto é também preparado por exfoliação, em meio aquoso, por meio da intercalação de lactato, enquanto o tetra-butilamónio é utilizado na exfoliação do óxido de níquel-cobalto. A resposta eletroquímica é avaliada em diferentes eletrólitos após reconstrução. Os resultados revelam a influência das espécies intercaladas durante o processo de exfoliação: quando a exfoliação é realizada para fins de armazenamento de energia, as espécies intercaladas e a força da interação com o material ativo devem ser consideradas de antemão para evitar o bloqueio superficial ou inibição da interação elétrodo-eletrólito. Os resultados mostraram que a exfoliação é uma rota promissora para aumentar a área de superfície ativa dos materiais, um parâmetro crítico no desempenho eletroquímico dos materiais dos eletrodos. Nesta dissertação é também estudado o mecanismo de carga-descarga do hidróxido de níquel-cobalto, que ainda não está completamente entendido. Assim, compreender esse mecanismo é um passo crítico para otimizar a morfologia e o desempenho do material e para projetar futuros dispositivos de armazenamento de energia. Para esclarecer os processos que ocorrem durante a carga, aplica-se o modelo de Mott-Schottky foi aplicado parade modo a avaliar a variação da conductividade do material e da sua capacidade na interface elétrodo-eletrólito. [...]

This thesis describes applications of advanced multinuclear solid-state nuclear magnetic resonance (NMR) experiments to the characterisation of industrially-relevant catalyst materials. Experiments on γ-Al₂O₃ introduce the use of solid-state NMR spectroscopy for the investigation of disordered solids. The existence of Al(V) sites on the surface of this material is demonstrated, showing that removal of adsorbed H₂O may facilitate a rearrangement effect in γ-Al₂O₃ that promotes the formation of these Al environments. A range of aluminium oxide-based supported metal catalysts has been investigated. Studies of these systems by ¹H and ²⁷Al solid-state NMR spectroscopy indicate that a metal-support interaction (MSI) exists between surface cobalt oxide crystallites and the γ-Al₂O₃ support, and is strongest for materials containing small, well dispersed Co oxide crystallites. It is shown that the hygroscopic nature of γ-Al₂O₃ allows the extent of the MSI to be visualised by ¹H MAS NMR, by observing the extent of the proton-metal oxide interaction resulting from the presence of adventitious adsorbed H₂O. The surface/bulk chemistry of Co spinel aluminate materials is also investigated. ¹H, ²⁹Si, ²⁷Al and ¹⁷O solid-state NMR techniques are used to gain insight into the structural nature of silicated alumina catalysts. The combination of isotopic enrichment and dynamic nuclear polarisation (DNP) surface-enhanced NMR spectroscopy can provide a definitive and fully quantitative description of the surface structure of Si-γ-Al₂O₃ (1.5 wt% Si), and the role of adventitious surface water is highlighted. Analysis of silicated aluminas prepared by “sequential grafting” and “single shot” approaches shows that silica growth on γ-Al₂O₃ follows two distinct morphologies. ¹⁷O gas exchange enrichment is also shown to be successful in facilitating ¹⁷O solid-state NMR studies of these materials. It is demonstrated that double (²⁹Si and ¹⁷O) enrichment of Si-γ-Al₂O₃ (1.5 wt% Si) can facilitate access to ²⁹Si-¹⁷O 2D correlation experiments, even at low silica loading. An exploratory investigation of Ti-alumina model catalysts has also been carried out using ¹H, ²⁷Al and ¹⁷O solid-state NMR spectroscopy. These studies indicate that Ti-γ-Al₂O₃ and Ti-Al M50 may be structurally distinct materials.

Les travaux de cette thèse ont été consacrés à la synthèse de nanoparticules magnétiques d'oxyde de fer et d'oxyde de cobalt et de nanoparticules coeur-coquille constituées d'un coeur d'oxyde de fer recouvert d'oxyde de cobalt et à l'élaboration de nanomatériaux - composites nanostructures carbonées/nanoparticules d'oxyde métallique - pour des applications dans le domaine biomédical et celui de l'énergie. Pour la synthèse des NPs, la forme et la taille des NPs sont fortement dépendantes des conditions de réaction (nature des ligands, des solvants, température de réaction ... ) , ce qui affecte leurs propriétés magnétiques. De plus, des simulations ont montré que les chaînes de stéarate peuvent désorber plus facilement les atomes de fer que les atomes de cobalt et se libérer pour former des germes, ce qui pourrait expliquer le comportement distinctif entre les deux complexes. Ces nanoparticules magnétiques ont été synthétisées à l'intérieur de nanotubes de carbone en deux étapes aboutissant à des taux de remplissage très importants. Après fonctionnalisation, ces nanocomposites ont été introduits dans de cellules tumorales et ont été magnétiquement manipulées. Ils se sont révélés être très efficaces en tant qu'agents de contraste en IRM mais également dans le domaine de l'hyperthermie (activation sous éclairage dans le domaine de !'Infrarouge proche). Enfin, de nouveaux composites à partir de nanoparticules de Nb20 5 et de graphène (ou NTCs) ont été synthétisés et des résultat~prometteurs ont été obtenus dans des tests de batterie lithium-ion : leur utilisation en tant qu'anode a permis d'obtenir des capacités réversibles de 260 mAh/g. / This thesis was focused on the synthesis of magnetic nanoparticles of iron oxide and cobalt oxide and core-shell nanoparticles, consisting of a cobalt oxide coated iron oxide and on the development of composite nanomaterials - nanostructures carbon /metal oxide nanoparticles - for applications in the biomedical field and the energy. For the synthesis of NPs, the shape and size of NPs are dependent of the reaction conditions, which further affect their magnetic properties. Meanwhile, simulation showed that stearate chains can desorb more easily from iron atoms and release to form seeds than from cobalt atoms, which might explain distinctive behavior between the bath complexes. Regarding nanostructures carbon/metal oxide nanoparticles hybrid materials, the properties of the filled magnetic CNTs as heat mediator for photothermal ablation and as contrast agent for MRI were then evaluated and promising results have been obtained. Last, new composite materials (Nb205 nanoparticles/graphene or NTCs) were synthesized and promising results were obtaines in lithium battery tests : their use as anode allowed obtaining reversible capacities of 260 mAh/g.

Coordination complexes [M(O2CCH2OC2H4OMe)2] (M = Co, 4; M = Mn, 5) are accessible by the anion exchange reaction between the corresponding metal acetates [M(OAc)2(H2O)4] (M = Co, 1; M = Mn, 2) and the carboxylic acid HO2CCH2OC2H4OMe (3). IR spectroscopy confirms the chelating or μ-bridging binding mode of the carboxylato ligands to M(II). The molecular structure of 5 in the solid state confirms a distorted octahedral arrangement at Mn(II), setup by the two carboxylato ligands including their α-ether oxygen atoms, resulting in an overall two-dimensional coordination network. The thermal decomposition behavior of 4 and 5 was studied by TG-MS, revealing that decarboxylation occurs initially giving [M(CH2OC2H4OMe)2], which further decomposes by M–C, C–O and C–C bond cleavages. Complexes 4 and 5 were used as CCVD (combustion chemical vapour deposition) precursors for the deposition of Co3O4, crystalline Mn3O4 and amorphous Mn2O3 thin films on silicon and glass substrates. The deposition experiments were carried out using three different precursor solutions (0.4, 0.6 and 0.8 M) at 400 °C. Depending on the precursor concentration, particulated layers were obtained as evidenced by SEM. The layer thicknesses range from 32 to 170 nm. The rms roughness of the respective films was determined by AFM, displaying that the higher the precursor concentration, the rougher the Co3O4 surface is (17.4–43.8 nm), while the manganese oxide films are almost similar (6.2–9.8 nm).

No description available.

Perovskite based materials have great potentials for various energy applications and the search for new materials for uses in SOFCs has largely been concentrated to this class of compounds. In this search, we have studied perovskite phases in the system La2Co1+z(Ti1-xMgx)1-zO6, with 0  x 0.9 and z = 0.0, 0.2, 0.4, 0.6. Crystal structures were characterized by XRD and, for selected compositions, also by NPD and SAED. They exhibit with increasing x, as well as increasing z, a progressive increase in symmetry from monoclinic to orthorhombic to rhombohedral. The main focus in this work has been on the investigation of structure-property relations for compositions with 0.0 x 0.5 and z = 0. The nominal oxidation state of Co increases for these with increasing x, from Co2+ for x = 0 to Co3+ for x = 0.5. Magnetic measurements and XANES studies showed that the average spin state of Co changes linearly with increasing x, up to x = 0.5, in accordance with varying proportions of Co with two fixed oxidation states, i.e. Co2+ and Co3+. The data suggests that the Co3+ ions have an IS spin state or a mixture of LS and HS spin states for all compositions with nominally only Co2+ and Co3+ ions, possibly with the exception of the composition with x = 0.1, 0.2 and z = 0, for which the data indicate that the spin state might be HS. The XANES data indicate furthermore that for the perovskite phases with z = 0 and x &gt; 0.5, which in the absence of O atom vacancies contain formally Co4+, the highest oxidation state of Co is Co3+, implying that the substitution of Ti4+ by Mg2+ for x ³ 0.5 effects an oxidation of O2- ions rather than an oxidation of Co3+ ions. The thermal expansion was found to increase nearly linearly with increasing oxidation state of Co. This agrees well with findings in previous studies and is attributable to an increase in the ionic radius of Co3+ ions with increasing temperature, due to a thermal excitation from a LS to IS or LS/HS spin states. High temperature electronic conductivity measurements indicate that the electronic conductivity increases with an increase of both relative and absolute amount of Co3+. The latter can be attributed to an increase in the number of Co-O-Co connections. Additional high temperature magnetic measurements for selected samples, whose susceptibilities did not follow a Curie law behaviour up to room temperature, showed effective magnetic moments that did approach plateaus even at high temperatures (900 K). Interpretations of these data are, however, hindered by the samples losing oxygen during the applied heating-cooling cycle. The present study has shown that the investigated system is suitable for further studies, of more fundamental character, which could provide further insight of the structure-property relationships that depend on the oxidation state of Co. / Studies of cobalt based perovskites for cathode materials in solid oxide fuel cells.