O desenho planar para as células a Combustível de Óxido Sólido (SOFC) é melhor do que o tubular devido a sua maior densidade de corrente e menor custo de fabricação. No entanto, o projeto de SOFC planar requer selantes para evitar o vazamento de combustível e a mistura de gases em altas temperaturas. Os vidros e os vitrocerâmicos têm demonstrado serem os mais adequados por apresentarem boa compatibilidade com outros componentes da célula nas temperaturas de trabalho das SOFCs (700-1000°C). No presente estudo, uma série de composições pertencentes ao sistema BaO-Al2O3-SiO2 (BAS) com a adição de B2O3 foram sintetizados tomando as proporções apropriadas de cada óxido constituinte. Propôs-se melhorar este sistema utilizando-se formadores e teores relevantes de modificadores estruturais, de forma a compatibilizar tanto o desempenho térmico por meio do coeficiente de expansão térmica (CET) como a compatibilidade química com os demais componentes da célula. A originalidade deste estudo está na busca destas características em regiões de composições ainda não exploradas, localizadas dentro do triangulo de compatibilidade BS-B2S-BAS2 na região rica em bário do sistema ternário. Entre estes vidros sintetizados quatro composições (BAS-4, BAS-5, BAS-6 e BAS-7) foram escolhidas porque são as mais adequadas às solicitações termomecânicas exigidas para um material vítreo atuar como selante em SOFC. / The design for planar cells Fuel Solid Oxide (SOFC) is better than the tubular due to its higher current density and lower manufacturing cost. However, the design of planar SOFC requires sealant to prevent leakage of fuel and the mixture of gases at high temperatures. Glasses and glass-ceramics have proven to be the most suitable because they have good compatibility with the other components of the cell at working temperature (700-1000°C). In the present study, a series of compositions belonging to the BaO-Al2O3-SiO2 (BAS) system with the addition of B2O3 were synthesized having the appropriate proportions of each component oxide. It was proposed to improve this system using relevant levels of formers and structural modifiers oxides, in order to match both the thermal performance of thermal expansion coefficient (TEC) and chemical compatibility with other components of the cell. The originality of this study is to search for these characteristics in regions of compositions not yet explored, located inside the compatibility triangle BS-B2S-BAS2 at the barium rich part of the ternary diagram. Among the synthesized glasses four batch compositions (BAS-4, BAS-5, 6-BAS, BAS-7) were chosen because best matched the thermo-mechanical required for a glassy material to act as SOFCs sealant.

Os materiais à base de céria (CeO2) e zircônia (ZrO2) estão presentes em diversas aplicações tecnológicas, destacando-se como anodo de células de combustível de óxido sólido (SOFC) e em catálise, tanto para a produção de hidrogênio, como na automotiva (Three-Way Catalysis). A solução sólida ZrxCe1-xO2- é de especial interesse, pois apresenta melhor estabilidade térmica e maior capacidade de armazenamento de oxigênio (OSC), quando comparada com os óxidos não dopados. Os materiais mesoporosos (poros de 2 a 50 nm) possuem elevada área superficial e permeabilidade a gases, características estas importantes para o desempenho das SOFCs e dos processos de catálise. Neste trabalho, zircônia-céria (Zr0,1Ce0,9O2-) mesoporosa foi sintetizada pelo processo sol-gel, utilizando, como precursores, os cloretos inorgânicos (ZrCl4 e CeCl3.7H2O), o copolímero em bloco P123 (PEO20PPO70PEO20) como direcionador de estrutura e o TIPB (tri-isopropil-benzeno) como agente dilatador. A solução passou por tratamento hidrotérmico durante 48h a 80°C, com posterior calcinação a 400°C para a remoção do polímero, resultando no óxido cristalizado. Na análise foram utilizadas as técnicas: difração de raios X em alto ângulo (XRD), espalhamento de raios X a baixo ângulo (SAXS), isotermas de adsorção de nitrogênio (NAI) e microscopia eletrônica de varredura e transmissão (SEM e TEM). Os resultados mostraram que o material possui elevada área superficial (110m2/g), mesoporos de várias dimensões, atingindo valores médios em torno de 30 nm, fase majoritariamente cúbica Fm3m e, em menor proporção, tetragonal P42/nmc. As micrografias revelaram que o óxido está totalmente nano-cristalizado, com os poros tipo fendas e uma mesoporosidade secundária com distribuição de tamanhos menor e mais estreita. Quatro amostras foram sintetizadas com diferentes razões em massa TIPB/P123 (0, 1, 2 e 4), de forma que foi possível verificar um aumento na dimensão dos poros devido à inclusão do dilatador. As demais propriedades estruturais e morfológicas mantiveram-se inalteradas entre todas as amostras, mesmo com diferentes quantidades de TIPB. / The ceria (CeO2) and zirconia (ZrO2) based materials are present in several technological applications, mainly as Solid Oxide Fuel Cells (SOFC) anodes and catalysts, for hydrogen production and automotive converter (Three-Way Catalysis). The solid solution ZrxCe1-xO2- has attracted special attention, since it shows better thermal stability and higher oxygen storage capacity (OSC), if compared to the non-doped oxides. The mesoporous materials (pores of 2 to 50 nm) show high surface area and gas permeability, important properties for SOFCs and catalysts efficiency. In this work, mesoporous ceria-zirconia (Zr0,1Ce0,9O2-) was synthesized by a sol-gel route using inorganic chlorides (ZrCl4 e CeCl3.7H2O) as precursors, block copolymer P123 (PEO20PPO70PEO20) as template and TIPB (tri-isopropyl-benzene) as swelling agent. The solution was submitted to hydrothermal treatment for 48h at 80°C and calcined at 400°C to remove the template, resulting in the crystallized oxide. The characterization was performed by X-ray diffraction at high angles (XRD), small angle X-ray scattering (SAXS), nitrogen adsorption isotherms (NAI) and transmission and scanning electron microscopy (TEM and SEM). The results showed that the material has high surface area (110m2/g), a wide pore size distribution with mean values around 30 nm, predominant cubic phase Fm3m and, in less quantity, tetragonal P42/nmc. The micrographs revealed that the oxide is totally nano-crystallized, having pores with slit shape and a secondary smaller mesoporosity with a narrow size distribution. Four samples were produced with different TIPB/P123 mass rate (0, 1, 2, 4), therefore was possible to verify the pore size expansion due to the swelling addition. The structural and morphological properties remained unchanged, even with different quantities of TIPB.

O desenvolvimento de novos materiais cerâmicos condutores de prótons é tecnologicamente importante devido às suas aplicações como eletrólitos em células a combustível de óxido sólido (SOFCs), dispositivos eletroquímicos fontes de energia limpa e renovável. Entre os desafios encontrados na aplicação nessas células de novos óxidos cerâmicos prótoncondutores está a alta resistividade de seus contornos de grão, que bloqueiam eletricamente a corrente de defeitos protônicos. Esse fato torna relevantes as pesquisas sobre a natureza desse fenômeno de bloqueio e sua relação com as características próton-condutivas do material. Nesta dissertação, investigamos as propriedades do sistema não estequiométrico Ba3Ca1,18Nb1,82O9-δ, juntamente com os compostos Ba3Ca1,18Nb1,52R0,3O9-δ (R = Y, Gd, Sm, Nd). Pós cristalinos dessas composições foram sintetizados via reação em estado sólido e utilizados na fabricação de cerâmicas. Os materiais foram caracterizados do ponto de vista estrutural, microestrutural, vibracional e elétrico, utilizando diversas técnicas físicas e correlacionado as características de cada composição às suas propriedades condutivas. Experimentos de difração de raios X e cálculos de fator de estrutura revelaram o aparecimento de ordenamento estrutural na estrutura perovskita de todos os sistemas sintetizados, sendo a intensidade de reflexões características utilizada como parâmetro de ordenamento. A microestrutura das cerâmicas foi otimizada em função do tempo de sinterização e as amostras finais obtidas apresentaram baixa porosidade. A caracterização vibracional das cerâmicas via espectroscopia Raman corrobora o resultado do ordenamento obtido via difração, além de indicar a presença ou preenchimento de vacâncias de oxigênio na rede cristalina dos materiais. Análises vibracionais também permitiram o estudo da acumulação de defeitos na borda das amostras cerâmicas e de sua estabilidade química, sendo tais diretamente correlacionadas à dopagem feita no material. O estudo de propriedades elétricas por espectroscopia de impedância aliado a modelagens por circuitos equivalentes permitiu separar propriedades elétricas de grão e contorno de grão. O efeito de bloqueio elétrico dos contornos pôde ser observado nas cerâmicas estudadas e está correlacionado à condutividade do interior dos grãos, sendo tais resultados interpretados à luz do modelo de cargas espaciais. / The development of novel proton conducting ceramic materials is technologically important due to their application as electrolytes in solid oxide fuel cells (SOFC), electrochemical devices that constitute clean and renewable energy sources. Among the challenges faced when applying new oxide materials to fuel cells is the high resistivity of grain boundaries, which causes an electrical blocking effect of proton transport. This issue stimulates research on the nature of the blocking phenomenon and its relation to proton-conducting properties of the materials. In the present study, we investigate physical properties of the non-stoichiometric system Ba3Ca1,18Nb1,82O9-δ together with the compounds Ba3Ca1,18Nb1,52R0,3O9-δ (R = Y, Nd, Sm, Gd). Crystalline powders of all the chemical compositions were synthetized by a solidstate reaction and used to prepare ceramic samples. The materials were characterized in terms of their structural, microstructural, vibrational and electrical properties by the usage of various physical techniques, correlating characteristics of each composition to its proton-conduction properties. X-ray diffraction experiments combined with structure factor calculations revealed the presence of perovskite structural ordering in all the compounds, and the intensity of characteristic reflections was used as ordering parameter. Ceramic microstructure was optimized with respect to sintering time and the final samples achieved low porosity. Vibrational characterization by Raman spectroscopy supported the ordering result obtained by diffraction and indicated the presence or filling of oxygen vacancies in the materials crystal structures. Vibrational analysis also allowed the study of defect accumulation near the ceramic samples edges and their chemical stability, which are directly related to material doping. Electrical studies by impedance spectroscopy together with equivalent circuit modeling allowed the separation of grain and grain boundary electrical properties. Blocking effect by the boundaries was observed on the considered samples and is correlated to conductivity on grain bulk. Blocking results are interpreted in the framework of a space charge model.

Dans le domaine des piles SOFC, un des principaux objectifs actuels est la réduction de latempérature de fonctionnement des cellules en deçà de 700°C, afin de garantir une plusgrande durabilité des systèmes électrochimiques et des matériaux de cellules. En outre, leprocédé d’élaboration d’une cellule complète comprend actuellement deux voire trois étapesde frittage; une seule opération de frittage pourrait conduire à une diminution conséquente ducoût de production de la cellule. Le but de ce travail de thèse est d’apporter une contribution àces deux problématiques en proposant un procédé d’élaboration d’une cellule de pile àcombustible SOFC en une seule opération dite de cofrittage et avec une sélection dematériaux à hautes performances électrochimiques.Cette thèse a été abordée selon trois thématiques principales : mécanique, microstructurale etélectrochimique.Après la caractérisation du comportement en frittage des matériaux retenus pour l’étude, uncycle de frittage conduisant à une microstructure d’électrolyte acceptable (porosité fermée) aété sélectionné. Le cofrittage a ensuite été étudié selon un aspect mécanique. Les phénomènesde courbure engendrés par le cofrittage ont été expliquées à l’aide d’une modélisationanalytique et confrontées à des observations in situ. Le travail s’est ensuite orienté dans uneapproche microstructurale avec l’optimisation de la microstructure de la cathode en utilisantune modélisation numérique basée sur la méthode des éléments discrets. Les composants de lacellule complète ont finalement été caractérisés par spectroscopie d’impédanceélectrochimique afin d’optimiser leurs performances. Enfin, une cellule complète exempt defissure a été réalisée par cofrittage et ses performances électrochimiques ont été estimées. / In the field of SOFCs, a major objective is the reduction of the cell operating temperaturebelow 700°C, in order to ensure greater durability of electrochemical systems and cellmaterials. In addition, the fabrication process of a complete cell currently includes two orthree stages of sintering. Thus one sintering process could lead to a consequent decrease in theproduction cost of the cell. The purpose of this thesis is to contribute to these two issues byproposing a method for manufacturing a SOFC fuel cell in a single operation called cofiringand with a selection of high electrochemical performance materials.This thesis is addressed in three main areas: mechanical, microstructural and electrochemical.After sintering behavior characterization of the selected materials, a sintering cycle leading toan acceptable electrolyte microstructure (closed porosity) was selected. The cofiring was thenapproached by a mechanical aspect. The curvature Phenomena caused by of cofiring wereexplained using an analytical model and compared with in situ observations. The work is thencontinued with a microstructural approach. The optimization of the cathode microstructurewas done using a numerical modeling based on the discrete element method. Cell componentswere finally characterized by electrochemical impedance spectroscopy to optimize theirperformances. Finally, a free crack complete cell was obtained by co-sintering process and herelectrochemical performance was estimated.

L'objectif de la thèse était d'étudier la faisabilité d'un couplage thermique entre un réservoir d'hydrure métallique et une source externe de chaleur. L'évolution des propriétés de composites à base d'hydrure de magnésium (MgH2) a été étudiée en fonction du nombre de cycles d'hydruration. On observe une très bonne stabilité de la capacité massique d'absorption sur le long terme (600 cycles réalisés). Les premiers cycles sont néanmoins marqués par une évolution importante de la microstructure qui dépend de la proportion et/ou de la nature de l'additif utilisé lors de la mécano-synthèse des poudre d'hydrure. Cette évolution est associée à une augmentation de la conductivité thermique, mais également à une légère dégradation des cinétiques intrinsèques de réaction ainsi qu'à une expansion volumique des composites. Nos mesures montrent que l'amplitude des contraintes mécaniques engendrées sur les parois d'un réservoir se stabilisent après une cinquantaine de cycles. Un réservoir contenant 10 kg de MgH2, et capable de stocker 6500 Nl d'hydrogène en 35 minutes a ensuite été développé au laboratoire. L'énergie des réactions d'absorption et de désorption est échangée avec une source externe de chaleur via un fluide caloporteur. Ce système permet de représenter l'intégration thermique d'un réservoir d'hydrure dans un système de cogénération. Un modèle numérique a été développé afin de mieux appréhender le comportement de ce réservoir. Des essais de couplage entre un réservoir de taille plus modeste et une pile à combustible haute température (SOFC) développant une puissance électrique de 1 kW ont également été réalisés au Politecnico di Torino. / The main target of the thesis was to study the thermal integration of a magnesium hydride (MgH2) tank with an external heat source. At first, the evolution of material properties upon cycling were investigated. A large microstructural evolution was observed during the first cycles which impacts on kinetics of reaction and thermal conductivity. An expansion of the composites is also observed. Quantity and/or nature of the additives used during material preparation was identified as an important parameter controlling this phenomenon. Our measures show that mechanical strains on the tank wall due to this expension are stable after 40 hydrogenation cycles. A large number of cycles was applied to these composites which exhibits a very high stability upon cycling. A large scale magnesium hydride tank (10 kg MgH2) storing 6500 Nl of hydrogen in 35 minutes was developed and tested. The energy of reaction is exchanged with an external heat source by a heat transfer fluid. This installation allows to simulate the integration of a magnesium hydride tank into a co-generation system. A numerical model was developed in order to better understand and predict the behavior of this tank. A thermal integration test of the MgH2 with a high temperature fuel cell (SOFC) was performed at Politecnico di Torino.

O desenvolvimento de novos materiais cerâmicos condutores de prótons é tecnologicamente importante devido às suas aplicações como eletrólitos em células a combustível de óxido sólido (SOFCs), dispositivos eletroquímicos fontes de energia limpa e renovável. Entre os desafios encontrados na aplicação nessas células de novos óxidos cerâmicos prótoncondutores está a alta resistividade de seus contornos de grão, que bloqueiam eletricamente a corrente de defeitos protônicos. Esse fato torna relevantes as pesquisas sobre a natureza desse fenômeno de bloqueio e sua relação com as características próton-condutivas do material. Nesta dissertação, investigamos as propriedades do sistema não estequiométrico Ba3Ca1,18Nb1,82O9-δ, juntamente com os compostos Ba3Ca1,18Nb1,52R0,3O9-δ (R = Y, Gd, Sm, Nd). Pós cristalinos dessas composições foram sintetizados via reação em estado sólido e utilizados na fabricação de cerâmicas. Os materiais foram caracterizados do ponto de vista estrutural, microestrutural, vibracional e elétrico, utilizando diversas técnicas físicas e correlacionado as características de cada composição às suas propriedades condutivas. Experimentos de difração de raios X e cálculos de fator de estrutura revelaram o aparecimento de ordenamento estrutural na estrutura perovskita de todos os sistemas sintetizados, sendo a intensidade de reflexões características utilizada como parâmetro de ordenamento. A microestrutura das cerâmicas foi otimizada em função do tempo de sinterização e as amostras finais obtidas apresentaram baixa porosidade. A caracterização vibracional das cerâmicas via espectroscopia Raman corrobora o resultado do ordenamento obtido via difração, além de indicar a presença ou preenchimento de vacâncias de oxigênio na rede cristalina dos materiais. Análises vibracionais também permitiram o estudo da acumulação de defeitos na borda das amostras cerâmicas e de sua estabilidade química, sendo tais diretamente correlacionadas à dopagem feita no material. O estudo de propriedades elétricas por espectroscopia de impedância aliado a modelagens por circuitos equivalentes permitiu separar propriedades elétricas de grão e contorno de grão. O efeito de bloqueio elétrico dos contornos pôde ser observado nas cerâmicas estudadas e está correlacionado à condutividade do interior dos grãos, sendo tais resultados interpretados à luz do modelo de cargas espaciais. / The development of novel proton conducting ceramic materials is technologically important due to their application as electrolytes in solid oxide fuel cells (SOFC), electrochemical devices that constitute clean and renewable energy sources. Among the challenges faced when applying new oxide materials to fuel cells is the high resistivity of grain boundaries, which causes an electrical blocking effect of proton transport. This issue stimulates research on the nature of the blocking phenomenon and its relation to proton-conducting properties of the materials. In the present study, we investigate physical properties of the non-stoichiometric system Ba3Ca1,18Nb1,82O9-δ together with the compounds Ba3Ca1,18Nb1,52R0,3O9-δ (R = Y, Nd, Sm, Gd). Crystalline powders of all the chemical compositions were synthetized by a solidstate reaction and used to prepare ceramic samples. The materials were characterized in terms of their structural, microstructural, vibrational and electrical properties by the usage of various physical techniques, correlating characteristics of each composition to its proton-conduction properties. X-ray diffraction experiments combined with structure factor calculations revealed the presence of perovskite structural ordering in all the compounds, and the intensity of characteristic reflections was used as ordering parameter. Ceramic microstructure was optimized with respect to sintering time and the final samples achieved low porosity. Vibrational characterization by Raman spectroscopy supported the ordering result obtained by diffraction and indicated the presence or filling of oxygen vacancies in the materials crystal structures. Vibrational analysis also allowed the study of defect accumulation near the ceramic samples edges and their chemical stability, which are directly related to material doping. Electrical studies by impedance spectroscopy together with equivalent circuit modeling allowed the separation of grain and grain boundary electrical properties. Blocking effect by the boundaries was observed on the considered samples and is correlated to conductivity on grain bulk. Blocking results are interpreted in the framework of a space charge model.

Ce travail, qui associe analyse d'image, modélisation morphologique et calculs par transformées de Fourier, s'inscrit dans la thématique classique de l'homogénéisation de milieux hétérogènes, et dans le cadre notoirement problématique de l'optimisation multifonctionnelle de matériaux multiphasiques. Les matériaux qui font l'objet de cette thèse, collecteur de courant et anode, sont des éléments critiques des piles à combustibles (PAC). Ce dispositif convertit une énergie chimique en électricité grâce à l'oxydation d'un combustible, et ne rejette que de l'eau. Les PAC développées dans le cadre du projet européen Evolve sont d'un type nouveau, combinant des architectures préexistantes. Leur performance est déterminée par la conductivité ionique et électronique d'une part, par la perméabilité et les surfaces d'échange entre phases solides et pores d'autre part. Dans le cas d'un contraste de propriétés infini entre les phases (pores et solide, milieux isolant et conducteur), les propriétés effectives dépendent fortement de la répartition spatiale (morphologie) des phases en présence. On s'intéresse, dans un premier temps, à la segmentation, à la description et à la modélisation 3D de couches de piles à combustible, à partir d'images 2D acquises en microscopie électronique à balayage. Les microstructures sont segmentées puis caractérisées par des descripteurs morphologiques. On développe des modèles de milieux aléatoires 3D multiphasiques représentatifs des milieux réels. Ceux-ci reposent sur des modèles Booléens et de Gaussiennes seuillées et sont paramétrés par des caractéristiques géométriques simples du matériau (fractions volumiques, covariances, échelles caractéristiques). Ils sont validés visuellement et quantitativement, à l'aide de données morphologiques. Dans un second temps, on s'intéresse à la prédiction des propriétés de transport, à l'aide d'outils numériques par transformées de Fourier. Un algorithme amélioré, qui s'affranchit de l'effet de Gibbs est proposé en conductivité et la méthode de Wiegman (2007) est utilisée en perméabilité. La perméabilité de milieux booléens idéaux est calculée puis comparée à divers estimateurs analytiques. La borne de Berryman-Milton, connue précédemment dans le cadre du milieu Booléen de sphères, est calculée analytiquement pour un milieu Booléen de cylindres à l'aide d'une formule exacte pour le covariogramme de cylindres. Les propriétés de conductivité ionique et électronique de l'anode, et sa perméabilité, sont ensuite prédites à l'aide des modèles de milieux aléatoires précédemment développés et validés. La perméabilité, particulièrement sensible à la morphologie, est calculée pour divers paramètres du modèle, dont les surfaces spécifiques entre phases solides et pores. Plusieurs matériaux virtuels aux propriétés améliorées sont proposés. / This work, which combines image analysis, Fourier methods and morphological models, focuses on the prediction and optimization of the transport properties of fuel cell materials in the classical framework of the homogenization of random media. The materials under study are critical layers found in fuel cells.These devices produce clean electrical energy (and water) from chemical fuel oxidation.The materials studied here are novel types of fuel cells that combine several preexisting architectures. Their performance is determined by the ionic and electronic conductivity, on the one hand, and by permeability and specific surfaces exchange between the solid and porous phases. For materials with highly-contrasted properties (pores and solid, isolating and conducting media), the effective properties strongly depend on the spatial arrangement (morphology) of the various phases.Fuel cell layers are first described and modeled using 2D scanning electron microscopy images and image analysis.Microstructures are characterized by morphological descriptors and realistic random 3D media, based on Boolean and Gaussian fields, are developed to represent the materials. The latter are parametrized by simple geometrical characteristics including volume fractions and covariances.They are visually and quantitatively validated using morphological data.Second, the transport properties are predicted numerically using Fourier methods. In conductivity, a modified algorithm is proposed to suppress the Gibbs artifacts. For permeability, the scheme of Wiegman (2007) is used.The permeability of ideal Boolean models is computed and compared with various analytical estimates.The Berryman-Milton bound, previously known for the Boolean model of spheres, is computed for a Boolean model of flat cylinders, using an analytical expression for cylinder covariogramm. The ionic and electronic conductivity of anode layers, and their permeability are predicted using previously developed models. The permeability, which strongly depends on the morphology, is computed for various values of the models' parameters, including the specific surface area between solid and phases.Several virtual materials with improved properties are proposed.

Dans les piles à combustible SOFC (Solid Oxide Fuel cell) de type monochambre (SC-SOFC), l’anode et la cathode, séparées par un électrolyte, sont situées dans une même chambre alimentée par un mélange de combustible et d’oxygène. L’électrolyte, n’ayant alors plus le rôle d’étanchéité entre les compartiments anodique et cathodique, peut être mis en forme par sérigraphie. Cependant, il est nécessaire d’avoir une barrière pour éviter la possible diffusion de l’hydrogène produit localement à l’anode vers la cathode, ce qui peut générer une chute de la tension. L’objectif de ce travail de thèse est de créer une barrière de diffusion localisée via la densification de la surface de l'électrolyte par un traitement laser. Le matériau sélectionné pour l’électrolyte est un oxyde mixte Ce0,9Gd0,1O1,95 (CGO) qui est déposé par sérigraphie sur une anode composite NiO-CGO. Deux types de lasers impulsionnels sont utilisés : un laser UV (λ = 248 nm) et un laser IR (λ = 1064 nm). Les caractérisations microstructurales réalisées ont permis de mettre en évidence les effets du traitement laser pour certaines combinaisons fluence – nombre de tirs, montrant un grossissement de grain de l’électrolyte ou bien des surfaces densifiées mais fissurées. Des modifications structurales et chimiques sur la surface ont été évaluées ainsi que la diffusion de gaz au travers des électrolytes modifiés tout comme leur conductivité électrique. Afin de mieux comprendre l'interaction laser-matière, une modélisation thermique a également été mise en œuvre. Finalement, les performances de piles SC-SOFC ont été améliorées pour les dispositifs présentant un grossissement de grain à la surface de l'électrolyte. / In single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are both exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte, but in the SC-SOFC configuration it does not play tightness role between compartments. For this reason, a porous electrolyte can be processed by screen printing. However, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode through the electrolyte that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte by a laser treatment. The material chosen for the electrolyte was cerium gadolinium oxide Ce0.9Gd0.1O1.95 (CGO) which is deposited by screen printing on a composite NiO-CGO anode. UV laser and IR laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Structural and chemical modifications on the surface were evaluated as well as the gas diffusion through the electrolytes and their electrical conductivity. In order to understand interaction between the laser and the material, thermal modelling was also developed. Finally, SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface, particularly, the power density has been enhanced by a factor 2.

O desenho planar para as células a Combustível de Óxido Sólido (SOFC) é melhor do que o tubular devido a sua maior densidade de corrente e menor custo de fabricação. No entanto, o projeto de SOFC planar requer selantes para evitar o vazamento de combustível e a mistura de gases em altas temperaturas. Os vidros e os vitrocerâmicos têm demonstrado serem os mais adequados por apresentarem boa compatibilidade com outros componentes da célula nas temperaturas de trabalho das SOFCs (700-1000°C). No presente estudo, uma série de composições pertencentes ao sistema BaO-Al2O3-SiO2 (BAS) com a adição de B2O3 foram sintetizados tomando as proporções apropriadas de cada óxido constituinte. Propôs-se melhorar este sistema utilizando-se formadores e teores relevantes de modificadores estruturais, de forma a compatibilizar tanto o desempenho térmico por meio do coeficiente de expansão térmica (CET) como a compatibilidade química com os demais componentes da célula. A originalidade deste estudo está na busca destas características em regiões de composições ainda não exploradas, localizadas dentro do triangulo de compatibilidade BS-B2S-BAS2 na região rica em bário do sistema ternário. Entre estes vidros sintetizados quatro composições (BAS-4, BAS-5, BAS-6 e BAS-7) foram escolhidas porque são as mais adequadas às solicitações termomecânicas exigidas para um material vítreo atuar como selante em SOFC. / The design for planar cells Fuel Solid Oxide (SOFC) is better than the tubular due to its higher current density and lower manufacturing cost. However, the design of planar SOFC requires sealant to prevent leakage of fuel and the mixture of gases at high temperatures. Glasses and glass-ceramics have proven to be the most suitable because they have good compatibility with the other components of the cell at working temperature (700-1000°C). In the present study, a series of compositions belonging to the BaO-Al2O3-SiO2 (BAS) system with the addition of B2O3 were synthesized having the appropriate proportions of each component oxide. It was proposed to improve this system using relevant levels of formers and structural modifiers oxides, in order to match both the thermal performance of thermal expansion coefficient (TEC) and chemical compatibility with other components of the cell. The originality of this study is to search for these characteristics in regions of compositions not yet explored, located inside the compatibility triangle BS-B2S-BAS2 at the barium rich part of the ternary diagram. Among the synthesized glasses four batch compositions (BAS-4, BAS-5, 6-BAS, BAS-7) were chosen because best matched the thermo-mechanical required for a glassy material to act as SOFCs sealant.

Les piles à combustible Solid Oxide Fuel Cell sont des systèmes de production d’électricité. Une cellule élémentaire est un multicouche constitué de matériaux céramiques et de métal. Elles sont très sensibles aux contraintes mécaniques générées lors des cycles thermiques et d’oxydo-réduction, limitant leur durée de vie.Ce travail a porté sur la détermination expérimentale des contraintes résiduelles dans des cellules SOFC à anode support en fonction des sollicitations du système. Parallèlement à des mesures in-situ en température, une approche multi-échelles a été développée pour évaluer les hétérogénéités de contraintes dans l’électrolyte liées à la forte anisotropie élastique de la zircone yttriée qui le constitue. Différentes techniques ont été mise en œuvre afin de couvrir les 3 ordres de contraintes. Les mesures à l’échelle macroscopique ont été effectuées par diffraction de rayons X de laboratoire (méthode des sin²(Ψ)). La microdiffraction de rayonnement synchrotron en mode faisceau blanc et monochromatique a permis, après un important travail d’amélioration du protocole de mesure et d’analyse, de déterminer les tenseurs complets de contraintes et déformations grain à grain dans l’électrolyte. Les déformations intra-granulaires ont été évaluées par une technique d’EBSD.Les résultats obtenus ont permis d’analyser les mécanismes principaux qui régissent les évolutions de contraintes dans l’électrolyte. Des hétérogénéités de contraintes entre grains liées à leurs orientations cristallographiques ont été mises en évidence. Au-delà du problème des SOFC, les techniques mises en œuvre ouvrent la voie aux validations expérimentales des modèles mécaniques poly-cristallins. / The Solid Oxide Fuel Cells (SOFC) are high-performance electrochemical devices for energy conversion. A single cell is composed of layers made of different ceramic materials and metal. The mechanical integrity of the cell is a major issue during its lifetime. Damage of the cells is mainly due to the high operating temperature, the “redox” behavior of the anode and the brittleness of the involved materials. In this work, residual stresses in the electrolyte of a planar anode-supported SOFC have been experimentally measured for different treatments of the cell. In situ analysis at various temperatures has been performed. A multi-scale approach has been developed to study the expected strain-stress heterogeneities in the electrolyte due to the strong elastic anisotropy of the involved material (yttria-stabilized zirconia). Different techniques have been used to determinate stresses at the 3 different orders. Macroscopic stresses were studied using the Sin2 method on a laboratory X-ray goniometer. The complete strain and stress tensors of individual grains in the electrolyte have been determinate, after various improvements in the technique, by combining the diffraction of white and monochromatic micro beams produced by synchrotron source. Strain variation into grains has been evaluated using EBSD.This study has identified the main phenomena that control the stresses variation in the electrolyte layer. Stresses heterogeneities from grain to grain have been found and linked to the crystallographic orientation. Beyond SOFC’s considerations, the techniques that have been developed should permit an experimental validation of mechanical modeling to polycrystalline materials.