Solid oxide fuel cell (SOFC) systems have the potential to provide highly efficient power generation systems capable of utilizing readily available hydrocarbons. It is hoped that these systems will be capable of replacing some of the conventional power systems and act to reduce overall emissions and increase energy efficiency. SOFC technology faces many challenges such as high cost, lifetime uncertainties, and long startup times; and these challenges have prevented SOFC technology from being widely adopted. Established methods for providing SOFC stack thermal management are either very costly, work against system design goals, or are unreliable. If SOFC thermal management needs could be reduced, it is possible that SOFC cost and lifetime could be improved. It is thought that promotion of thermal radiation within a SOFC stack may add thermal control which will reduce the need for stack thermal management. Radiation may be promoted by decreasing the length: hydraulic diameter ratio of cathode flow channels and by increasing the manifold size to create a larger stack radiation enclosure. Full thermal tests of a SOFC stack are difficult and expensive, and due to this simulations of a SOFC are widely used to analyze stack thermal behavior. In this work, a model of a SOFC “unit cell” is adjusted to represent modern SOFC stacks. The proposed methods for radiation promotion are tested with simulations using this model, and conclusions of radiation promotion in SOFC stacks are provided. Additionally, radiative properties of commonly used materials are obtained through experiments, and future work for reducing stack reliance on active thermal management is proposed.

Deposition of Sm0.5Sr0.5CoO3 (SSC) films on Gd-doped ceria (GDC) substrates by electrostatic assisted ultrasonic spray pyrolysis (EAUSP) was demonstrated in this study. The XRD results indicate that crystalline phase with perovskite structure was obtained in the calcined films. SEM observations indicate that applied voltage and deposition temperature have profound effects on the film morphology in EAUSP method. Stronger applied voltage results in the smoother film while higher deposition temperature results in rougher film. A unique thick porous film with column structure is obtained for the first time by EAUSP method using a deposition temperature of 400 oC, an applied voltage of 10 kV and a deposition time of 600 seconds. The growth mechanism of the unique porous thick film is also discussed in this study. The area specific resistance (ASR) values of SSC cathode with this unique porous columnar structure are comparable to that obtained by conventional sample preparation routes. For example, an ASR value of 0.204 £[¡Ecm2 at 600 oC is obtained in this work. Electrostatic spray deposition (ESD) method was also employed to deposit SSC films as cathode on GDC substrates in this study. Crystalline SSC with perovskite structure was obtained in the calcined films. Deposition parameters including deposition temperature, precursor flow rate and deposition time were systematically varied to obtain the SSC films with various morphologies. The best film structure for high electrochemical performance is a porous reticular structure obtained under a precursor solution flow rate of 2.0 ml/hr and a deposition temperature of 350 oC. The growth mechanism of this reticular structure is established based on the examination of film evolution in a series of films obtained with different deposition times. The minimum ASR value of the porous reticular SSC cathode fabricated by ESD is 0.09 £[¡Ecm2 at 600 oC. SSC nano-wires were successfully synthesized by electro-spinning method. The diameter of calcined nano-wires ranges from 40 to 90 nm. The TEM results indicate that the calcined (800oC/2hr) SSC nano-wires are polycrystalline with an orthorhombic perovskite structure. SSC nano-fibers were then obtained from the SSC nano-wires through an ultrasonic vibration of 15 minutes. Electrodes of SSC nano-fiber on GDC substrate were then prepared by slurry printing method. The ASR values of SSC nano-fiber electrodes are extremely low and the minimum ASR value is 0.06 £[¡Ecm2 at 600 oC.

Solid Oxide Fuel Cells (SOFCs) have been researched for operation on anaerobic digester (AD)-derived biogas at wastewater treatment plants (WWTPs). SOFCs can perform well on light hydrocarbon fuels and the use of AD-derived biogas provides an opportunity for biogas to be used as a renewable fuel. Tests were conducted at three levels of H2 dilution (using N2, Ar and CO2 as diluent gases, plus H2O) to examine the performance of tubular SOFCs. When gases that are inert in SOFC reactions are used there is a decrease in cell performance. When CO2 was used the decrease in cell performance was higher due to the reverse water-gas shift (WGS) reaction reducing the partial pressure of H2. A computer simulation was developed to predict SOFC system efficiency and GHG emissions. The simulation indicated that the system electrical efficiency is higher for a S/C ratio of 2 then a S/C ratio of 1 due to the increased partial pressure of H2 in the reformate. The reduction in GHG emissions is estimated to be approximately 2,400 tonnes CO2, 60 kg CH4 and 18 kg N2O, annually. Testing was conducted using a simulated biogas reformate mixture that was developed through a research initiative in which urban areas with populations over 150,000 in the United States and 50,000 in Canada were solicited to participate in a survey of biogas composition. The biogas reformate composition was determined to be 66.7% H2, 16.1% CO, 16.5% CO2 and 0.7% N2, which was then humidified to 2.3 and 20 mol% H2O. The reformate tests conducted at the higher humidification level yielded a better performance than those at the lower humidification because the WGS reaction produced more H2 when additional H2O was provided. It was concluded that WWTP AD-derived biogas, when cleaned effectively to remove H2S, Si compounds, halides and other contaminants, could be reformed to provide a clean, renewable fuel for SOFCs. Biogas/SOFC systems could provide electricity and heat to WWTPs, as well as reduce GHG emissions, thus reducing their energy costs and environmental impact. / Thesis (Master, Civil Engineering) -- Queen's University, 2012-08-31 15:38:28.122

One of the major trends of development of solid oxide fuel cells is to reduce the operating temperature from the high temperature range (>950°C) and intermediate temperature range (750-850°C) to the low temperature range (450-650°C). Development of low temperature oxygen ion conducting electrolytes is focused on single-phase materials including Bi2O3 and CeO2-based oxides. These materials have high ion conductivity at the low temperature range, but they are unstable in reducing environments and they are also electronic conductors. In the present research, three types of multiphase materials, Ce0.887Y0.113O1.9435 (CYO)-ZrO2, CYO- yttria-stabilized zirconia (YSZ), and CuO-CYO were investigated. We found that the conductivity of multiphase electrolyte CuO-CYO with a mass ratio of 1:3 is at least 4 times greater than that of CYO and 10 times greater than that of YSZ, the most commonly used material, obtained in the present experiments at 600°C. The enhancement of conductivity in multiphase materials correlates with the level of mismatch between the two phases. Large mismatches in terms of valance and structure result in high vacancy density and hence high oxygen ion conductivity at grain boundaries. This study demonstrates that synthesis of multiphase ceramic materials is a feasible new avenue for development of oxygen ion electrolyte material for low temperature SOFCs.

One of the major technical challenges towards a viable H2S//Air SOFC is to identify and develop anode materials that are electronically conductive, chemically and electrochemically stable, and catalytically active when exposed to H2S-rich environments. The corrosive nature of H2S renders most traditional state-of-the-art SOFC anode materials (Ni, Pt, Ag) useless for long-term cell performance even at very low sulfur concentrations. In my doctoral thesis work, a new class of perovskite-based anodes was developed for potential use in SOFCs operating with H2S and sulfur-containing fuels. Cermets from this family of materials have shown excellent chemical stability and electrochemical performance at typical SOFC operating conditions. As an added benefit, they appear to preferentially oxidize H2S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements obtained using various H2S-H2-N2 fuel mixtures. Cell power output values were among the highest reported in the literature and showed no significant deterioration during 48-hour testing periods. Impedance measurements indicated overall cell resistances decreased with increasing temperature and H2S content of the fuel. This behavior is starkly different from that of contemporary SOFC anodes, where the presence of H2S usually increases overall polarization resistance and ultimately destroys the cell. Results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC power systems.

Ces travaux portent sur la recherche de matériaux alternatifs d’électrolyte ou d’électrodes de piles à combustible à oxyde solide. Une méthodologie basée sur la composition de l’oxyborate La26O27(BO3)8, développé à l’IMN, a permis de mettre en évidence deux matériaux prometteurs : Ba3Ti3O6(BO3)2 et K3Sb4O10(BO3). La synthèse de poudres de Ba3Ti3O6(BO3)2 et de phases substituées sur les sites du Ba ou du Ti ont été réalisés par voie solide à 950 °C. Les mesures de conductivité ont été effectuées par EIS sur des échantillons denses (compacité ≥ 90 %). Sous air, la conductivité est purement anionique et dépasse 10-4 S.cm-1 à 700 °C. Elle augmente pour les composés substitués par un élément de valence supérieure, et inversement. Sous atmosphère hydrogénée, une forte augmentation de conductivité est observée (x 200), liée à l’apparition d’une contribution électronique. Une étude couplant DRX, XPS et ATG montre que cette contribution est due à une réduction de 5 % du Ti4+ en Ti3+ et que cette réaction est réversible. Les calculs DFT ont permis de déterminer les énergies de formation et de migration des défauts dans le matériau. L’oxyborate K3Sb4O10(BO3) a été obtenu sous forme de monocristaux et de poudre. Une étude approfondie de la densification a été nécessaire afin d’obtenir des échantillons denses (compacité ≈ 90 %), en utilisant un broyage planétaire et/ou une aide au frittage. La conductivité du matériau sous air est de l’ordre de 10-3 S.cm-1 à 700 °C. Ces travaux mettent en évidence pour la première fois des niveaux de conductivité (ioniques et/ou électroniques) importants dans les oxyborates. Cette approche peut être appliquée à la recherche de matériaux alternatifs pour SOFC. / This work focuses on the search for alternative electrolyte or electrodes materials for solid oxide fuel cells. A methodology based on the composition of the La26O27(BO3)8 oxyborate, developed at the IMN, revealed two promising materials: Ba3Ti3O6(BO3)2 and K3Sb4O10(BO3). Syntheses of powders of Ba3Ti3O6(BO3)2 and substituted phases on the Ba or Ti atomic site were carried out by solid state reaction at 950 °C. Conductivity measurements were carried out by electrochemical impedance spectroscopy on dense samples (relative density ≥ 90 %). Under air, the conductivity is purely anionic and exceeds 10-4 S.cm-1 at 700 °C. Conductivity increases for compounds substituted with a supervalent element, and vice versa. In a hydrogen containing atmosphere, a large increase of conductivity is observed (x 200), linked to the appearance of an electronic contribution. A study combining XRD, XPS and TGA shows that this contribution is due to the reduction of 5 % of the Ti4+ in Ti3+ and that this reaction is reversible. DFT calculations allowed to determine the formation energies and the migration barriers of the defects in the material. K3Sb4O10(BO3) oxyborate was obtained as single crystals and powder. A thorough study of the densification of the material was necessary in order to obtain dense samples (relative density ≈ 90 %), using ball milling and/or sintering aid. The conductivity of the material in air is about 10-3 S.cm-1 at 700 °C. This work highlights significant conductivity levels (ionic and/or electronic) observed for the first time in oxyborates. This approach can be applied to find alternative materials for SOFC.

The aim of this thesis is to propose the design process and considerations to be employed in the fabrication of a high-volumetric-power-density intermediate temperature solid oxide fuel cell (IT-SOFC), as well as the necessary characterization and analysis techniques for such a device. A novel hexagonal honeycomb design will be proposed with functionally graded electrodes and an alternative electrolyte – a previously unexplored configuration based on attained research. The potential use of CFD software to investigate mass and heat transport properties of an SOFC having such a design shall be discussed, as well as the utility of experimental methods such as the generation of a polarization curve and the use of SEM to characterize electrochemical performance and microstructure, respectively. Fabrication methods shall also be evaluated, and it will be shown that the proposed design is not only feasible but meets the goal of designing an SOFC with a power density of 2 W/cm3 operating at or below 650 C.

Distributed generation (defined as the production of power in small quantities at the point of use) has recently gained significant interest due to its benefits over a centralized approach. This thesis investigates the integration of a natural gas fed solid-oxide fuel cell (SOFC) and compressed air energy storage (CAES) technologies for distributed generation at the building-level scale. The SOFC/CAES system is also integrated with multiple vital sub-systems (including on-site solar panels) for the building to provide the heat, through an in-floor heating system, hot water, and power demanded by the building. This thesis investigates the models for the SOFC/CAES system, and implements them in a generic analysis tool providing a means for rapid analysis of a wide variety of case studies. The analysis tool determines the ability of the SOFC/CAES system to follow the power and heat loads demanded by the building, and evaluates its performance with an assortment of metrics, including efficiencies, CO2 emissions and grid-independence. The SOFC/CAES system was investigated for the new ExCEL building at McMaster University. It was found that the system was able to produce upwards 75% of the heat and hot water demand, and upwards of 94% of the power demand of the building. When compared to the current state-of-the-art natural gas based power producing technology and high efficiency furnace, the SOFC/CAES system reduces the CO2 emissions associated with the building by a minimum of 8.7% and a maximum of 26.95%. The cost of electricity for the system is significantly (21% to 150%) more costly than current market prices; however the SOFC/CAES system is the least costly of all other distributed generation technologies investigated for the case of the ExCEL building. / Thesis / Master of Applied Science (MASc)

O mundo moderno é extremamente dependente de combustíveis fósseis como fonte de energia primária e essa forte dependência leva a problemas políticos, econômicos e ambientais. Como possível solução a esses problemas tem-se as células combustíveis, pois são dispositivos que geram energia elétrica limpa diretamente de reações eletroquímicas produzindo, além da energia elétrica, apenas calor e água. Logo, percebe-se que essas células são fontes de energia confiáveis, renováveis e não poluentes, que contribuem para o desenvolvimento sustentável. Devido a isso, este trabalho teve como objetivo principal a síntese (por um método inédito) e a caracterização de materiais porosos a base de cromita de lantânio, LaxSr1-xCryFe1-y(Mn1-y)O3-?, para possível implementação como material de anodo e catodo de célula a combustível de óxido sólido (SOFC). Particularmente, estudos com anodos nos quais o transporte eletrônico é feito por materiais cerâmicos ao invés de metais são a área mais promissora na pesquisa recente. Além disso, materiais a base de manganita de lantânio dopadas com estrôncio são na atualidade os materiais mais usados na construção do catodo da SOFC. Nesta tese os materiais foram sintetizados pelo método sol-gel com agentes direcionador e dilatador de estrutura, resultando em materiais porosos em forma de esponja e com a estrutura perovskita, porém com fases espúrias. Foi estudada a influência do processamento de calcinação e de dopagem sobre as estruturas cristalográficas e porosas dos materiais. A maior temperatura de calcinação favoreceu a formação da estrutura perovskita com a retenção da fase romboédrica e reduziu a presença das fases espúrias, porém reduziu a porosidade, principalmente dos menores mesoporos, e a área superficial dos materiais. Por outro lado, ao dopar o sítio B os materiais com 75 %mol de La e calcinação a 1000 °C, observou-se a formação de um maior volume de mesoporos, ao mesmo tempo, que produziu uma maior quantidade de mesoporos menores e favoreceu a retenção da fase romboédrica da estrutura perovskita. Quanto ao comportamento eletrocatalítico, as células com eletrodos confeccionados a partir de La0,33Sr0,66Cr0,33Mn0,33O3-? apresentaram os melhores resultados tanto para anodo como para catodo entre as amostras avaliadas na tese. Além do mais, foram obtidos dois materiais, um cerâmico (La0,33Sr0,66Cr0,33Mn0,33O3-?) e um compósito cerâmico (La0,33Sr0,66Cr0,33Mn0,33O3-? + ZrO2 8%mol Y2O3) bons candidatos a catodo da SOFC. Esses materiais possuem uma composição química não encontrada na literatura para tal finalidade, ou seja, são inéditos. / The modern world is extremely dependent on fossil combustibles as primary source of energy and, this dependence brings political, economic and ambient problems. As a possible solution to these problems are the fuel cells, because they are devices that generate clean electric energy directly from electrochemical reactions, producing besides electric energy, heat and water. Therefore, these cells are reliable, renewable and non-pollutant sources, that contribute to the sustainable development. Related to it, this work had the main goal the synthesis (by a new method) and characterization of porous materials based on lanthanum chromite, LaxSr1-xCryFe1-y(Mn1-y)O3-?, for possible use as anode and cathode material of Solid Oxide Fuel Cell (SOFC). In particular, studies of anodes in which the electronic transport is performed by ceramic materials instead of metals are the most promising recent research area. Moreover, materials based on lanthanum manganite doped with strontium are now a days the more used materials for SOFC cathodes. In this thesis, the materials were synthesized by the sol-gel method with directing and swelling structure agents, resulting in porous sponge materials with perovskite structure, but having spurious phases. The influence of the calcination and doping of the materials upon the crystallographic and porous structures were studied. Higher calcination temperature favored the formation of the perovskite structure and reduced the presence of spurious phases, but reduced the porosity, mainly of smaller mesopores and the surface area. On the other hand, doping the B site in materials with 75 %mol of La and the calcination at 1000 oC produced a higher mesopore volume, a higher amount of small mesopores and favored the retention of the rhombohedral perovskite structure. Regarding the catalytic behavior, the cells with electrodes of La0,33Sr0,66Cr0,33Mn0,33O3-? presented the best results as anode and cathode among the evaluate samples. Moreover, two materials were obtained, a ceramic one, (La0,33Sr0,66Cr0,33Mn0,33O3-?) and a ceramic composite, (La0,33Sr0,66Cr0,33Mn0,33O3-? + ZrO2 8%mol Y2O3), good candidates as SOFC cathodes. These materials have a chemical composition, which were not reported in the literature for this application, being unique.

A obtenção do Cermet de níquel-zircônia via moagem de alta energia (Mechanical Alloying MA) foi estudado visando a preparação de anodos de células a combustível de óxido sólido (SOFC). O níquel metálico foi adicionado em três concentrações: 30, 40 e 50% em volume. As operações de moagem foram conduzidas em moinho vibratório de alta energia do tipo SPEX. Estudou-se a influência do tempo de moagem, a eficiência de aditivos para controle do processo, tipo e geometria dos potes de moagem. A influência destas variáveis foram avaliadas através de análises de tamanho de partículas, determinação de área superficial e morfologia do material resultante. O uso de pote de teflon resultou em contaminação por carbono. Por outro lado, o uso de pote de aço aumenta a contaminação por impurezas metálicas. As diversas geometrias projetadas para os potes mostraram que potes com maiores raios de concordância (R.15) apresentaram melhor rendimento. Após a conformação e sinterização a 1300°C em atmosfera de argônio, as amostras apresentaram valores de densidade entre 60 a 80% da densidade teórica. As microestruturas observadas por microscopia eletrônica de varredura revelaram uma boa homogeneidade na distribuição de fases do Cermet. A técnica de moagem de alta energia apresentou-se como boa opção na fabricação de Cermet Ni-ZrO2. / The ZrO2 and metallic Ni Cermet obtained by Mechanical Alloying MA is studied in the present work with the objective to prepare solid oxide fuel cells anodes (SOFC). Metallic Ni is added under three different concentrations: 30, 40 and 50% volume. The millings were conducted in SPEX vibratory mill where the influence of milling time, process control additives efficiency, type and geometry of milling vessels were studied. The study of the influence of these variables was made under particle size analysis, surface area determination and resulting material morphology. The use of teflon vessel causes contamination by carbon. On the other side, steel vessel increases the contamination by metallic impurities. The several geometries projected and analyzed for the vessels showed that vessels with larger bottom radius (R.15) showed the best results. After conformation and sintering at 1300°C in argon atmosphere the samples reached densities between 60 and 80% of the theoretical density. Microstructures observed by scanning electron microscopy reveal good homogeneity in the Cermet phases distribution. The mechanical alloying technique was considered a good option to obtain Ni- ZrO2 Cermet.