Pós nanocristalinos de zircônia estabilizada com ítria ou escândia (YSZ ou ScSZ) entre 8 e 12 mol% foram sintetizados por meio dos métodos da poliacrilamida, dos precursores poliméricos e da precipitação simultânea de cátions. Os pós de partida foram analisados por difração de raios X (DRX), distribuição de tamanho de partículas por espalhamento laser, adsorção gasosa (BET), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), análise térmica simultânea, fluorescência de raios X (FRX), e espectroscopia de absorção óptica no infravermelho por refletância difusa (DRIFT). Os métodos de síntese por via úmida orgânica produziram pós nanocristalinos a partir de 550 °C, enquanto que o método da precipitação simultânea de cátions produziu pós amorfos que cristalizaram em torno de 450 °C com entalpias de cristalização -13,7 ± 0,6 kJ.mol-1 para 8YSZ e -11,7 ± 0,5 kJ.mol-1 para 12YSZ. Os valores de área de superfície específica obtidos para os pós sintetizados por meio dos métodos da poliacrilamida, dos precursores poliméricos e da precipitação (calcinados em ~ 650 °C) foram 27, 61 e 110 m2.g-1, respectivamente. Os pós obtidos pelo método da poliacrilamida apresentaram menor estado de aglomeração e maior quantidade de carbonato superficial relativamente ao pó obtido pelo método dos precursores poliméricos. A sinterização dos compactos de pós cerâmicos foi avaliada por meio da técnica de espectroscopia de impedância (EI) e dilatometria. Após sinterização, as cerâmicas foram analisadas por DRX, MEV e EI. Os resultados evidenciaram que os pós apresentaram elevada sinterabilidade, mas baixa densidade final por causa do estado de aglomeração dos pós. A adsorção de água à temperatura ambiente foi medida em um microcalorímetro Setaram Calvet e um sistema de dosagem Micromeritics. Foram feitos experimentos de calorimetria de solução por inserção de amostra em um calorímetro duplo tipo Calvet usando 3Na2O.4MoO3 como solvente. Estes experimentos, combinados com os de calorimetria de adsorção de água, permitiram determinar por meio de um ciclo termodinâmico, as entalpias de superfície para superfícies hidratadas e anidras. / Nanocrystalline yttria or scandia stabilized zirconia (YSZ, ScSZ) powders with fluorite-type structure were synthesized by the polyacrylamide, the polymeric precursor and the precipitation methods. Powders were characterized by X-ray diffraction (XRD), simultaneous (TG and DTA or DSC) thermal analysis, nitrogen adsorption analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and diffuse reflectance infrared Fourier transform absorption spectroscopy (DRIFT). The organic precursor methods produced nanocrystalline powders at approximately 550 °C and the precipitation method produced amorphous powders which crystallized at approximately 450 °C into a fluorite phase with crystallization enthalpies of -13.7 ± 0.6 kJ.mol-1 for 8YSZ and -11.7 ± 0.5 kJ.mol-1 for 12YSZ. The measured surface area of powders after calcination at 650 - 800 °C were 27 m2.g-1, 61 m2.g-1 and 110 m2.g-1 for the polyacrylamide, the polymeric precursor and the precipitation methods, respectively. The sintering process of the pressed ceramic powders was evaluated by direct impedance spectroscopy (IS) measurements and by dilatometry. Thereafter, the sintered pellets were analyzed by XRD, SEM and IS. The sintering studies show that the powders prepared by the chemical route have high sinterability; however, they do not sinter to high density as a result of dense aggregates in the initial powders. The heats of water adsorption at room temperature were measured on samples using a Setaram Calvet microcalorimeter and a Micromeritics gas dosing system. Drop solution calorimetry experiments were performed in a custom made Calvet twin calorimeter using sodium molybdate 3Na2O.4MoO3 solvent. These experiments, combined with water adsorption calorimetry, allowed for deriving, through a thermodynamic cycle, the surface enthalpies for hydrous and anhydrous surfaces.

La pile à combustible Solid Oxide Fuel Cell (PAC-SOFC) est un système de production d’énergie « propre » qui permet de convertir de l’hydrogène en énergie électrique en ne rejetant que de l’eau. Une nouvelle configuration appelée « monochambre » semble être particulièrement attrayante compte tenu de ces nombreux avantages sur la configuration bi-chambre classique : simplification de fabrication, baisse de la température de fonctionnement, utilisation d’hydrocarbures comme combustible… La mise en place d’un tel système implique le développement de nouveaux matériaux d’électrodes satisfaisants à de nouveaux critères. L’évaluation en condition réaliste de 7 matériaux de cathode potentiels par diverses caractérisations structurale, texturale et catalytique à mis en évidence la difficulté de développer un matériau possédant toutes les caractéristiques requises. Ainsi, un matériau présentant le meilleur compromis est proposé. Une bibliothèque de 15 catalyseurs supportés (3 métaux et 5 supports différents) a ensuite été développée. Ces catalyseurs, ayant pour but d’être intégrés dans l’anode de la pile pour réaliser le reformage d’hydrocarbures, ont été évalués selon une approche combinatoire en condition réaliste (présence d’hydrocarbure, d’eau, de dioxyde de carbone), ce qui a permis de sélectionner les catalyseurs imprégnés de platine, plus robuste notamment en présence d’eau. Finalement, le couplage de la spectroscopie d’impédance avec la chromatographie en phase gaz a permis d’évaluer le comportement électrochimique d’une nouvelle architecture anodique comportant un catalyseur issu de la bibliothèque. Les tests ont montré que l’ajout d’un catalyseur est bénéfique pour la diminution des résistances de polarisation anodiques par production localisée d’hydrogène à partir d’hydrocarbure. / Solid Oxide Fuel Cell is a device for “clean” electricity production from chemical energy. The new configuration called “single-chamber” seems to be very attractive with several advantages over bi-chamber conventional configuration: easier manufacturing, lowering of working temperature, possible use of hydrocarbons as fuel… Such configuration involves the development of new electrode materials satisfying new requirements. The evaluation of 7 potential cathode materials through several characterizations has shown that a compromise has to be found since one material does not exhibit all the requested features. A library of 15 supported catalysts (3 metals and 5 supports) was developed. These catalysts, aimed at be located inside the anodic cermet, were evaluated through a combinatorial approach in realistic condition (presence of hydrocarbon, water, carbon dioxide). Platinum-based catalysts are found the most robust, especially in presence of water. Finally, innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise a new anodic architecture with an enclosed Pt-based catalyst previously evaluated. Tests revealed the beneficial effect of the catalyst insertion over anodic polarisation resistance by hydrogen production from hydrocarbon.

Planare keramische Hochtemperaturbrennstoffzellen liefern aufgrund ihres hohen Wirkungsgrades sowie einer hohen Variabilität geeigneter Brennstoffe einen wertvollen Beitrag zur ressourcenschonenden Stromproduktion. Für einen sicheren Betrieb dieser Brennstoffzellen sind hermetisch dichte und elektrisch isolierende Dichtungen unabdingbar. Aufgrund ihrer chemischen Stabilität sowie der Anpassung relevanter Fügeeigenschaften wie Viskosität und thermischem Ausdehnungsverhalten eignen sich insbesondere teilkristalline Glaslote als Dichtungs- und Fügewerkstoffe für diese Aufgabe. Für einen zuverlässigen Langzeitbetrieb von Brennstoffzellensystemen ist neben der Anpassung der Fügeparameter ein umfassendes Verständnis der Alterungsprozesse von Glasloten im Fügeverbund unter Betriebsbedingungen hinsichtlich Gasdichtheit und elektrischem Iso-lationsvermögen von entscheidender Bedeutung. In grundlegenden Untersuchungen zeigt diese Arbeit auf, welche vielschichtigen Degradationsprozesse in teilkristallinen Glasloten unter simulierten Einsatzbedingungen ablau-fen. Durch geeignete Versuchsabläufe gelang es, diese Einflüsse hinsichtlich ihrer Auswirkungen auf Degradationsprozesse zu separieren und zu bewerten. Die daraus gewonnenen Erkenntnisse flossen in eine Glaslotentwicklung ein, mit der die Degradationsstabilität teilkristalliner Glaslote unter den gegebenen Einsatzbedingungen deutlich erhöht werden konnte. Besondere Berücksichtigung fand hierbei der Einfluss der Glaszusammensetzung auf Degradationsprozesse im Verbund mit den metallischen Fügepartnern sowie die Porenbildung in gesinterten glaskeramischen Gefügen unter brennstoffzellentypischen Betriebsbedingungen. Im Gesamtergebnis zeigt die vorliegende Arbeit, dass zur Erfüllung von Fügeaufgaben neben der Anpassung intrinsischer Glasloteigenschaften auch das langfristige Verhalten teilkristalliner Glaslote im Fügeverbund Berücksichtigung finden muss.:Einleitung Grundlagen von Brennstoffzellen Funktionsweise von Brennstoffzellen Einteilung von Brennstoffzellen Unterteilung keramischer Hochtemperaturbrennstoffzellen Planare Hochtemperaturbrennstoffzellen Aufbau und Werkstoffe Dichtungen für planare Hochtemperaturbrennstoffzellen Glimmerdichtungen Aktiv- und Reaktivlotdichtungen Glaslotdichtungen Verbunddichtungen Glaslotdichtungen in planaren Hochtemperaturbrennstoffzellen Eigenschaften von Glas und Glaskeramik Fügen keramischer Brennstoffzellenstapel mit Glasloten Degradation von Glasloten in SOFCs Stand der Technik – Literatur Motivation dieser Arbeit Material und Methoden Verwendetes Glaslotsystem Metallsubstrate Erhitzungsmikroskopie Dilatometrie Röntgenographische Phasenanalyse Qualitative Heißgasextraktion Chemische Analysen Ermittlung des elektrischen Widerstandes Versuchsaufbau kompakter Glasproben Versuchsaufbau für Auslagerung unter dualer Atmosphäre Ermittlung der Heliumleckrate Gefügeanalyse Ergebnisse und Diskussion Charakterisierung des Standardglaslotes S01 Auslagerung bei Verwendung inerter Elektroden an Luft Spannungsfreie Auslagerung zwischen Goldsubstraten Spannungsfreie Auslagerung zwischen Crofer 22 APU- und Gold-Substraten Auslagerung unter elektrischer Spannung, Kombination A: beide Elektroden aus Gold Auslagerung unter elektrischer Spannung, Kombination B: Anode Gold, Kathode Crofer 22 APU Auslagerung unter elektrischer Spannung, Kombination C: Anode Crofer 22 APU, Kathode Gold Auslagerung unter elektrischer Spannung, Kombination D: beide Elektroden aus Crofer 22 APU Auslagerungen unter relevanten Betriebsbedingungen Charakterisierung des Ausgangszustand des Gefüges Auslagerung unter dualer Atmosphäre ohne elektrische Spannung Auslagerung unter dualer Atmosphäre mit elektrischer Spannung Auswirkungen verzögerter elektrischer Spannung Beschleunigte Degradation durch erhöhte elektrische Spannung Langzeitauslagerungen unter dualer Atmosphäre Glaslotentwicklung für keramische Brennstoffzellen Mechanismen von Porenbildung im Glaslot Glaslote mit erhöhter Stabilität gegenüber Blasenbildung Erhöhung der Stabilität gegenüber metallischen Fügepartnern Untersuchung von Fügeeigenschaften ausgewählter Glaslote Auslagerungen neu entwickelter Glaszusammensetzungen Degradationsverhalten modifizierter ZnO-haltiger Glaslote Degradationsverhalten ZnO-freier Glaslote Zusammenfassung Ausblick Anhang Abkürzungen, Formelzeichen und Einheiten Abbildungsverzeichnis Tabellenverzeichnis Literaturverzeichnis

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Solid Oxide Fuel Cells are fuel cells that operate at high temperatures usually in the range of 600oC to 1000oC and employ solid ceramics as the electrolyte. In Solid Oxide Fuel Cells oxygen ions (O2- ) are the ionic charge carriers. Solid Oxide Fuel Cells are known for their higher electrical efficiency of about 50-60% [1] compared to other types of fuel cells and are considered very suitable in stationary power generation applications. It is very important to study the effects of different parameters on the performance of Solid Oxide Fuel Cells and for this purpose the experimental or numerical simulation method can be adopted as the research method of choice. Numerical simulation involves constructing a mathematical model of the Solid Oxide Fuel Cell and use of specifically designed software programs that allows the user to manipulate the model to evaluate the system performance under various configurations and in real time. A model is only usable when it is validated with experimental results. Once it is validated, numerical simulation can give accurate, consistent and efficient results. Modeling allows testing and development of new materials, fuels, geometries, operating conditions without disrupting the existing system configuration. In addition, it is possible to measure internal variables which are experimentally difficult or impossible to measure and study the effects of different operating parameters on power generated, efficiency, current density, maximum temperatures reached, stresses caused by temperature gradients and effects of thermal expansion for electrolytes, electrodes and interconnects. iv Since Solid Oxide Fuel Cell simulation involves a large number of parameters and complicated equations, mostly Partial Differential Equations, the situation calls for a sophisticated simulation technique and hence a Finite Element Method (FEM) multiphysics approach will be employed. This can provide three-dimensional localized information inside the fuel cell. For this thesis, COMSOL Multiphysics® version 4.2a will be used for simulation purposes because it has a Batteries & Fuel Cells module, the ability to incorporate custom Partial Differential Equations and the ability to integrate with and utilize the capabilities of other tools like MATLAB ® , Pro/Engineer® , SolidWorks® . Fuel Cells can be modeled at the system or stack or cell or the electrode level. This thesis will study Solid Oxide Fuel Cell modeling at the cell level. Once the model can be validated against experimental data for the cell level, then modeling at higher levels can be accomplished in the future. Here the research focus is on Solid Oxide Fuel Cells that use hydrogen as the fuel. The study focuses on solid oxide fuel cells that use 3-layered, 4-layered and 6-layered electrolytes using pure YSZ or pure SCSZ or a combination of layers of YSZ and SCSZ. A major part of this research will be to compare SOFC performance of the different configurations of these electrolytes. The cathode and anode material used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively

The potential of Solid Oxide Fuel Cell Gas Turbine (SOFC/GT) hybrid systems for fuel flexibility makes this technology greatly attractive for system hybridization with various fuel processing units in advanced power generation systems and/or polygeneration plants. Such hybrid technologies open up the possibility and opportunities for improvement of system reliabilities and operabilities. However, SOFC/GT hybrid systems have not yet reached their full potential in term of capitalizing on the synergistic benefits of fuel cell and gas turbine cycles. Integrating fuel cells with gas turbine and other components for transient operations increases the risk for exposure to rapid and significant changes in process dynamics and performance, which are primarily associated with fuel cell thermal management and compressor surge. This can lead to severe fuel cell failure, shaft overspeed, and gas turbine damage. Sufficient dynamic control architectures should be made to mitigate undesirable dynamic behaviours and/or system constraint violations before this technology can be commercialized. But, adequate understanding about dynamic coupling interactions between system components in the hybrid configuration is essential. Considering this critical need for system identification of SOFC/GT hybrid in fuel flexible systems, this thesis investigates the dynamic performance of SOFC/GT hybrid technology in response to fuel composition changes. Hardware-based simulations, which combined actual equipment of direct-fired recuperated gas turbine system and simulated fuel cell subsystem, are used to experimentally investigate the impacts of fuel composition changes on the SOFC/GT hybrid system, reducing potentially large inaccuracies in the dynamic study. The impacts of fuel composition in a closed loop operation using turbine speed control were first studied for the purpose of simplicity. Quantification of safe operating conditions for dynamic operations associated with carbon deposition and compressor stall and surge was done prior to the execution of experimentation. With closed loop tests, the dynamic performance of SOFC/GT hybrid technology due to a transition in gas composition could be uniquely characterized, eliminating the interactive effects of other process variables and disturbances. However, for an extensive system analysis, open loop tests (without turbine speed control) were also conducted such that potential coupling impacts exhibited by the SOFC/GT hybrid during fuel transients could be explored. Detailed characterization of SOFC/GT dynamic performance was performed to identify the interrelationship of each fuel cell variable in response to fuel composition dynamics and their contributions to operability of the system. As a result of lowering LHV content in the fuel feed, which involved a transition from coal-derived syngas to humidified methane composition in the SOFC anode, the system demonstrated a dramatic transient increase in fuel cell thermal effluent with a time scale of seconds, resulting from the conversion of fuel cell thermal energy storage into chemical energy. This transient was highly associated with the dynamics of solid and gas temperatures, heat flux, heat generation in the fuel cell due to perturbations in methane reforming, water-gas shifting, and electrochemical hydrogen oxidation. In turn, the dramatic changes in fuel cell thermal effluent resulting from the anode composition changes drove the turbine transients that caused significant cathode airflow fluctuations. This study revealed that the cathode air mass flow change was a major linking event during fuel composition changes in the SOFC/GT hybrid system. Both transients in cathode air mass flow and anode composition significantly affected the hybrid system performance. Due to significant coupling between fuel composition transitions and cathode air mass flow changes, thermal management of SOFC/GT hybrid systems might be challenging. Yet, it was suggested that modulating cathode air flow offered promise for effective dynamic control of SOFC/GT hybrid systems with fuel flexibility. / Thesis / Doctor of Philosophy (PhD)

The global electricity generation industry is very reliant on the use of fossil fuels, particularly natural gas and coal. However, it is quickly becoming a reality that the over-consumption of these resources will continue to lead to significant global damage via global warming, ecosystem destruction, and the depletion of these so-called non-renewable re-sources. To combat this issue, renewable sources such as wind, biofuels and solar are be-coming much more prevalent in the power generation industry, but significant economic, reliability and availability barriers to entry will prevent these sources from being major contributors to the power industry for decades. To this end, this thesis focuses on the design, operation, optimization and life cycle analysis of an integrated solid-oxide fuel (SOFC) cell power plant integrated with com-pressed air energy storage (CAES). This plant, fueled by either natural gas or coal, can make much more efficient use of their limited non-renewable fuel sources, and are capable of achieving nearly 100% carbon capture at the plant boundary. This plant is intended to serve as a more efficient and environmentally responsible alternative to current power generation methods while still exploiting remaining fossil fuels to their fullest extent. This thesis details the design, sizing and simulation of integrated SOFC/CAES plants in Aspen Plus so that full feasibility and techno-economic analyses may be performed, the results of which are then compared to the current state-of-the-art (SOTA) options. In order to compare the plants on an environmental level, full cradle-to-grave life-cycle analyses using the ReCiPe 2008 method are completed for each SOFC-based plant and all comparable SOTA options under a wide range of assumptions and plant configurations, such as the use of carbon capture strategies. Furthermore, detailed reduced-order dynamic models of the integrated SOFC/CAES plants are developed and simulated with a newly developed rolling-horizon optimization method to assess the load-following capabilities of the integrated plant. Real scaled demand data for the market of Ontario, Canada for the years 2013 and 2014 are used as the demand data for the simulations. This thesis takes strides in proving the feasibility of an integrated SOFC/CAES power plant for providing clean, efficient, reliable and cost-effective power using fossil fuels. The next steps for this project involve the development of a lab-scale pilot plant, which would be used to validate simulation results and provide an opportunity for the real-time application and assessment of the potential of this plant design. / Thesis / Doctor of Philosophy (PhD)

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