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1
Nguyen, Ty, and ty nguyen@csiro au. "Preparation, Characterisation and Cell Testing of Gadolinium Doped Cerium Electrolyte Thin Films for Solid Oxide Fuel Cell Applications." RMIT University. Electrical and Computer Engineering, 2008. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20081030.110755.
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Solid Oxide Fuel Cells (SOFCs) are devices that directly convert chemical energy into electrical energy, without proceeding through a Carnot combustion cycle. These devices are based on the usage of solid oxide electrolytes operating at relatively elevated temperatures. Two major hurdles must be overcome in order to decrease the operating temperatures of practical SOFCs. The first relates to reducing ohmic losses within solid electrolytes. The second relates to the need for developing high performance electrodes since electrolyte reaction rates at both anode and cathode are affected detrimentally as operating temperatures fall. This PhD project has focussed on addressing the first hurdle in two innovative ways: 1. the implementation of solid electrolytes with higher ionic conductivity than zirconia, 2. the development of very thin film electrolytes as thick as 5Ým. Several thin films with novel electrode-electrolyte structures were fabricated and evaluated in order to demonstrate the viability of low temperature SOFC operations. Development of such thin films was innovative and challenging to achieve. The approach taken in this work involved fabricating a dense and thin gadolinia doped ceria (10GDC - Gd 10wt%, Ce 90wt%) oxide electrolyte. 10GDC is an electrolyte exhibiting higher conductivities than conventional materials during low temperature operations. A research contribution of this PhD was the demonstration of the deposition of 10GDC thin films using RF magnetron sputtering for the first time. 10GDC thin film electrolytes with thickness in a range between 0.1 to 5Ým were fabricated on 10 yttrium stabilised zirconium (10YSZ) substrates by using a RF magnetron sputterer. The primary parameters controlling 10GDC thin film deposition using this method were explored in order to identify optimal conditions. The fabricated films were subsequently analysed for their morphology, composition and stoichiometry using a variety of methods, including Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray Spectrometry (EDS), optical microscopy, X-ray Photoelectron Spectroscopy (XPS), and X-ray Diffraction (XRD). A preliminary test was conducted in order to examine the function of 10GDC thin film electrolytes together with the cathode and anode substrates at intermediate temperatures (700oC). A complete planar single cell was designed and assembled for this purpose. However, when fully assembled and tested, the cell failed to generate any voltage or current. Consequently, the remainder of the PhD work was focused on systematically exploring the factors contributing to the assembled fuel cell failure. As fabrication failure analysis is seldom reported in the scientific literature, this analysis represents a significant scientific contribution. This analysis proceeded in a series of steps that involved several different methods, including SEM, red dye analysis, surface morphology and cross section analysis of the cell. It was found that pinholes and cracks were present during the fuel cell operating test. Cathode delamination was also found to have occurred during the test operation. This was determined to be due to thermal expansion mismatch between the cathode substrate and the 10GDC electrolyte thin film. A series of suggestions for future research are presented in the conclusion of this work.
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Yung, Hoi, and 容海. "Synthesis and structure optimization of gadolinium doped ceria-platinum composite for intermediate temperature solid oxide fuel cellcathode." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48199266.
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Solid oxide fuel cells (SOFC), owing to its high operating temperatures, have many advantages over other types of fuel cells. Its commercialization, however, relies greatly on its costs and long term durability. By reducing the operating temperature to the intermediate temperature range, the costs for the balance of plant would be significantly reduced. The greatest contribution to cell over-potential at this temperature range is the oxygen reduction at cathode; hence development of a cathode material with low specific resistance and durability would have direct impact on the commercialization of SOFC.
Composite cathode is a common strategy used by many to improve cathode performance. This was done conventionally by random mixing of cathode material with a better ionic conductor such as the electrolyte material. Impregnation or infiltration is often used to improve interconnectivity among individual phases in the composite, In this study, fabrication of a composite cathode with two phases - gadolinium doped ceria (GDC) and platinum attempted, forming two inter-locked networks each with a channel dimension in the nanometer range by hard templating and chemical vapor infiltration (CVI) both for the first time to the best of my knowledge. It was found that surface layer of these materials play a very important role in the performance and structural stability. Another set of composite cathode was fabricated by packing commercially available GDC with carbon pore-former following by impregnation with Pt/Ag-Pt alloy. By introducing small amount of silver (6wt%), area specific resistance of 0.94cm2 and 0.16cm2 were observed at 550C and 660C, respectively during impedance spectroscopy in symmetrical cell arrangement. Silver was proposed to provide greater effective surface area for surface exchange and extending the triple phase boundary. Platinum was also suggested to provide a surface where silver wetting is possible stabilizing morphology of silver in the GDC scaffold.
Platinum is not a practical choice of electrode material due to its costs and lower performance, it was chosen to demonstrate the strategy of vapor phase infiltration in fabricating SOFC composite cathode. However, the technique of CVI demonstrated can potentially be applied to other cathode candidate materials.published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy
3
Dougherty, Troy Allen. "Synthesis and characterisation of ordered mesoporous materials." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1023.
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Ordered mesoporous materials have attracted much attention recently for use in a wide range of applications. The oxidising materials, ceria (CeO₂) and CGO (Ce₀.₉Gd₀.₁O[subscript(2-δ)]) have both been synthesised with ordered mesopores, but a method for the simple fabrication of these materials in high yields with crystalline pore walls has not yet been reported in the literature. This thesis details the development of the vacuum impregnation method for the synthesis of ordered mesoporous materials with emphasis on ceria and CGO. Using the vacuum impregnation method both materials were successfully prepared. The materials exhibited the porous single crystal morphology in high yields, with unusual crystallographic features. Nitrogen physisorption, transmission electron microscopy (TEM), TEM tomography and temperature programmed studies were employed. Temperature programmed studies showed the materials to be catalytically active at lower temperatures than traditionally-prepared ceria. Photovoltaic studies showed that the materials exhibited efficient exciton quenching. The observation of nanowire extrusion during the synthetic procedure assisted in the postulation of a mechanism for product formation in the vacuum impregnation method. The vacuum impregnation method was subsequently shown to be applicable to the synthesis of other materials, with encouraging results presented for ordered mesoporous carbon and Zr₀.₈₄Y₀.₁₆O[subscript(2-δ)]. The syntheses of ordered mesoporous La₀.₈₅Sr₀.₁₅GaO[subscript(3-δ)] and La₀.₇₆Sr₀.₁₉CoO[subscript(3-δ)] were unsuccessful.
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Green, Robert David. "Carbon Dioxide Reduction on Gadolinia-Doped Ceria Cathodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1232574534.
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Swaroop, Sathya, Martin Kilo, and Ilan Riess. "Determination of transport properties of gadolinia doped ceria powders from SIMS profiles." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193120.
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Swaroop, Sathya, Martin Kilo, and Ilan Riess. "Determination of transport properties of gadolinia doped ceria powders from SIMS profiles." Diffusion fundamentals 7 (2007) 15, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14172.
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Sønderby, Steffen. "Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-102513.
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Solid oxide fuel cells convert chemical energy directly into electrical energy with high efficiency and low emission of pollutants. However, before fuel cell technology can gain a significant share of the electrical power market, the operation temperature needs to be reduced in order to decrease costs and improve the durability of the cells. Application of thin film electrolytes and barrier coatings is a way of achieving this goal. In this thesis, I have investigated film growth and microstructure of yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) thin films deposited by physical vapor deposition. The aim is to make industrially applicable coatings suitable for application in solid oxide fuel cells (SOFCs). For this purpose, the coatings need to be thin and dense. YSZ coatings were prepared by pulsed direct current (DC) magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) in both laboratory- and industrial-scale setups. Industrial-scale pulsed DC magnetron sputtering of YSZ showed that homogenous coating over large areas was possible. In order to increase film density of the YSZ, HiPIMS was used. By tuning deposition pressure, peak power density and substrate bias voltage it was possible to deposit noncolumnar thin films without voids and cracks as desired for SOFC applications. CGO coatings were deposited by pulsed DC magnetron sputtering with the purpose of implementing diffusion barriers to prevent reactions between Sr from the SOFC cathode and the electrolyte. A model system simulating a SOFC was prepared by depositing thin CGO and YSZ layers on cathode material. This setup allowed the study of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. The study revealed Sr to diffuse along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased. CGO thin films were implemented in metal-based SOFC and the influence of film microstructure and thickness on the electrochemical performance of the cell was studied. Cell tests showed that an area specific resistance (ASR) down to 0.27 Ωcm2 could be obtained 650 °C with sputtered CGO barrier layers in combination with a lanthanum strontium cobaltite cathode. In comparison a spin-coated CGO barrier resulted in an ASR value of 0.50 Ωcm2. This shows the high effectiveness of the sputtered barrier in obtaining state-of-the-art performance. In summary, this work provides fundamental understanding of the deposition and growth of YSZ and CGO thins films and proves the prospective of employing thin film barrier coating in order to obtain high-performing SOFCs.
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Chen, Haiyan. "Probing Defects and Electronic Processes on Gadolinia-doped Ceria Surfaces Using Electron Stimulated Desorption." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10427.
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Probing Defects and Electronic Processes on Gadolinia-doped Ceria Surfaces Using Electron Stimulated Desorption
Haiyan Chen
133 Pages
Directed by Professor Thomas M. Orlando
Polycrystalline gadolinia-doped ceria (GDC) has been widely investigated as a promising low temperature solid oxide fuel cell (SOFC) electrolyte and as part of composite electrodes. In this thesis, electron stimulated desorption (ESD) has been used to probe the defect related electronic properties of GDC surfaces and the interactions of water and molecular oxygen with these surfaces.
In particular, the electron irradiation induced surface charging of GDC has been found to be dependent on the incident electron energy: negative at lower energy and positive at higher energy. Trapping of electrons and holes by the gadolinium aggregated, oxygen vacancy rich grain boundaries has been considered as the origin of surface charging. Depending on the sample treatment, there can be various defects, hydroxyl groups, chemically adsorbed water molecules, or water dimers on GDC surfaces. Water and molecular oxygen interact primarily with defect sites.
Systematic investigations of electron stimulated O+ desorption have yielded activation energies relevant to oxygen vacancy production on ceria surfaces, and to surface positive charge dissipation related to ionic conduction of GDC. Highly efficient electron stimulated O+ desorption from GDC surfaces has been attributed to the lowered charge density on oxygen ions coordinated with oxygen vacancy clusters and thus may be used as a probe for surface defect types.
Electron stimulated desorption of O2+ from GDC surfaces during molecular oxygen adsorption has shown the ability of ESD to detect chemically adsorbed O2. The velocity distributions of O2+ can be used to probe intermediate adsorption species such as O2, as well as the positive charge of the surface.
Overall, this thesis has demonstrated that ESD can provide important information on the kinetics and dynamics of surface charging, charge transport, adsorption and reactions occurring at defective insulating metal oxides materials. The abilities to probe the defects and their roles in surface processes make ESD a valuable technique for surface chemistry and catalysis studies.
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Ralph, James Michael. "A study of doped ceria electrolytes." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/7782.
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PORFIRIO, TATIANE C. "Influencia do calcio e do litio na sinterizacao e na condutividade eletrica do oxido de cerio contendo gadolinio." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9951.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Livermore, Stephanie J. A. "Fuel reforming catalysis and characterisation of intermediate temperature ceria-gadolinia based solid oxide fuel cells." Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391138.
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Mewafy, Basma. "Etude de surface d'électrodes Ni-cermet dans des conditions d'électrolyse à vapeur à température intermédiaire." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF041.
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Les cellules d'électrolyse à oxyde solide (SOEC) sont des dispositifs électrochimiques à haute température dans lesquels l'eau se dissocie en hydrogène et en oxygène sous un potentiel appliqué. La technologie SOEC offre un potentiel énorme pour la production future massive d’hydrogène et montre une grande dynamique pour devenir compétitive sur le plan commercial par rapport à d’autres technologies d’électrolyse (par exemple, l’électrolyse à membrane polymère ou alcaline), mieux établies mais plus coûteuses et moins efficaces. Ceci est principalement dû au fait que l'augmentation de la température de fonctionnement permet de réduire considérablement la demande en énergie électrique, ce qui permet des rendements de conversion d'énergie électrique à chimique élevés. À la baisse, les dispositifs des pays de l’Europe centrale et orientale jusqu’à présent ne sont toujours pas viables commercialement, principalement en raison de la difficulté à trouver des matériaux qui répondent aux exigences de haute performance et de durabilité aux températures de fonctionnement élevées. L'objectif général de cette thèse est de traiter les deux inconvénients majeurs qui entravent la pénétration de la technologie SOEC sur le marché de l'énergie, à savoir les taux de dégradation élevés et le coût des équipements. La dégradation de la voltage au cours du vieillissement de la cellule est l’indicateur de performance qui se traduit par une augmentation du overpotential qu’il faut appliquer à une cellule d’électrolyse afin de maintenir une production constante d’hydrogèneSolid Oxide Electrolysis Cells (SOEC) are high temperature electrochemical devices where water dissociates to hydrogen and oxygen under an applied potential. SOEC technology has a huge potential for future mass production of hydrogen and shows great dynamics to become commercially competitive against other electrolysis technologies (e.g. alkaline or polymer membrane electrolysis), which are better established but more expensive and less efficient. This is mainly due to the fact that by increasing the operating temperature the demand in electrical energy is significantly reduced, allowing high electrical-to-chemical energy conversion efficiencies. On the downside, up to now SOECs devices are still not commercially viable mainly due to the difficulty to find materials that fulfill the high-performance and durability requirements at high operating temperatures. The general objective of this thesis is to deal with the two major drawbacks that hamper the penetration of SOEC technology in the energy market, namely high degradation rates and device cost. Voltage degradation during the ageing of the cell is the performance indicator which is translated in an increase on the overpotential that has to be applied to an electrolysis cell in order to maintain constant hydrogen production
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Sønderby, Steffen. "Physical Vapor Deposition of Yttria-Stabilized Zirconia and Gadolinia-Doped Ceria Thin Films for Fuel Cell Applications." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-84611.
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In this thesis, reactive sputter deposition of yttria-stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) thin films for solid oxide fuel cell (SOFC) applications have been studied. All films have been deposited under industrial conditions. YSZ films were deposited on silicon wafers as well as commercial NiO-YSZ fuel cell anodes. The texture, morphology, and composition of the deposited films were investigated with respect to deposition parameters such as bias voltage which was identified as a key parameter to tailor the texture of the film and promote less columnar coatings when depositing on Si. In contrast, films grown on NiO-YSZ fuel cell anodes were seen to be randomly orientated when deposited at low substrate bias voltages. When the bias voltage was increased the film took over the orientation of underlying substrate due to substrate template effects. The deposited coatings were found to be homogeneous large areas within the coating zone, which is highly important for industrial applications. The performance of sputtered CGO thin films as diffusion barriers for stopping Sr diffusion between SOFC cathodes and electrolytes was also studied. This was done by introducing the sputtered CGO films in a metal-based SOFC setup. The performance depended on the density of the barrier layer, signifying that Sr diffusion and SrZrO3 formation is an issue. Area specific resistances down to 0.27 Ωcm2, corresponding to a maximum power density up to 1.14 W cm−2 at 650 °C could be obtained with sputtered CGO barrier layers in combination with Sr-doped lanthanum cobalt oxide cathodes which is a significant improvement compared conventional ceramic SOFCs. The diffusion mechanism of Sr through sputtered CGO films was investigated. For this purpose, a model system simulating a SOFC was prepared by depositing CGO and YSZ on cathode material. This setup allowed observation of Sr diffusion by observing SrZrO3 formation using X-ray diffraction while annealing. Electron microscopy was subsequently performed to confirm the results. It was found that Sr diffused along column/grain boundaries in the CGO films but by modifying the film thickness and microstructure the breaking temperature of the barrier could be increased.
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ARAKAKI, ALEXANDER R. "Obtencao de ceramicas de ceria - samaria - gadolinia para aplicacao como eletrolito em celulas a combustivel de oxido solido (SOFC)." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9506.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Kawano, Mitsunobu. "Studies on Ni-samaria-doped ceria cermet anode for solid oxide fuel cells." 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136300.
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Graves-Brook, Melissa Kaye. "Synthesis and characterization methods of palladium-doped ceria-zirconia compounds." Master's thesis, Mississippi State : Mississippi State University, 2005. http://sun.library.msstate.edu/ETD-db/ETD-browse/browse.
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Batista, Rafael Morgado. "Efeitos da atmosfera de sinterização e do tamanho de partícula na sinterização da céria-gadolínia." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-04122014-143143/.
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Os efeitos da atmosfera de sinterização e do tamanho inicial das partículas na sinterização da céria contendo 10% em mol de gadolínia (GdO1,5) foram sistematicamente estudados neste trabalho. Materiais de partida com três valores para a área de superfície específica foram utilizados, 210 m2/g, 36,2 m2/g e 7,4 m2/g. Diferentes cinéticas de sinterização foram verificadas. Quanto menor o tamanho inicial das partículas, menor é a temperatura para o início da sinterização e mais acelerada a densificação do material. Curvas mestres de sinterização foram construídas para cada um dos materiais analisados. Um programa computacional foi especialmente desenvolvido para este propósito. Diferenças significativas entre as energias de ativação para densificação foram verificadas. Para este trabalho foi determinado que, quanto menor o tamanho inicial de partícula, menores as energias de ativação. A evolução das distribuições de tamanhos de cristalitos foi investigada para os materiais de maior área superficial específica. Foi determinado que a eliminação e migração de poros (pore drag) é o mecanismo predominante para o crescimento de grãos durante o início da sinterização da céria gadolínia. Os efeitos da atmosfera de sinterização no desvio de estequiometria, na densificação, na evolução microestrutural e na condutividade elétrica da céria-gadolínia foram analisados. Atmosferas redutoras, oxidantes e inertes foram usadas para este propósito. Desvios na estequiometria da céria foram verificados no volume do material, sendo este dependente da área de superfície específica e da atmosfera utilizada. Quanto maior o potencial de redução da atmosfera utilizada, maior a concentração de Ce3+ no material. Com o aumento da concentração de Ce3+ um aumento no tamanho médio de grãos foi verificado. Uma diminuição na condutividade elétrica total, intra e intergranular foram determinadas para as amostras sinterizadas em atmosferas redutoras.The effects of the sintering atmosphere and initial particle size on the sintering of ceria containing 10 mol% gadolinia (GdO1.5) were systematically investigated. The main physical parameter was the specific surface area of the initial powders. Nanometric powders with three different specific surface areas were utilized, 210 m2/g, 36,2 m2/g e 7,4 m2/g. The influence on the densification, and micro structural evolution were evaluated. The starting sintering temperature was verified to decrease with increasing on the specific surface area of raw powders. The densification was accelerated for the materials with smaller particle size. Sintering paths for crystallite growth were obtained. Master sintering curves for gadolinium-doped ceria were constructed for all initial powders. A computational program was developed for this purpose. The results for apparent activation energy showed noticeable dependence with specific surface area. In this work, the apparent activation energy for densification increased with the initial particle size of powders. The evolution of the particle size distributions on non isothermal sintering was investigated by WPPM method. It was verified that the grain growth controlling mechanism on gadoliniadoped ceria is the pore drag for initial stage and beginning of intermediate stage. The effects of the sintering atmosphere on the stoichiometry deviation of ceria, densification, microstructure evolution, and electrical conductivity were analyzed. Inert, oxidizing, and reducing atmospheres were utilized on this work. Deviations on ceria stoichiometry were verified on the bulk materials. The deviation verified was dependent of the specific surface area and sintering atmosphere. Higher reduction potential atmospheres increase Ce3+ bulk concentration after sintering. Accelerated grain growth and lower electrical conductivities were verified when reduction reactions are significantly present on sintering.
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Yoshida, Hiroyuki. "Studies on Sintering Behaviors and Local Structures of Doped Ceria Compounds for Solid Oxide Fuel Cells." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147628.
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Kimpton, Justin Andrew, and jkimpton@physics unimelb edu au. "Conductivity and microstructural characterisation of doped Zirconia-Ceria and Lanthanum Gallate electrolytes for the intermediate-temperature, solid oxide fuel cell." Swinburne University of Technology, 2002. http://adt.lib.swin.edu.au./public/adt-VSWT20060727.084311.
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Lowering the operating temperature of the high-temperature, solid oxide fuel cell (SOFC) improves both the thermodynamic efficiency and the lifetime of this energy efficient technology. Unfortunately the rate of oxygen-ion transport through the solid electrolyte is temperature dependent, and materials previously employed as electrolytes in the high-temperature SOFC perform poorly at intermediate temperatures. Therefore new oxygen-ion conductors with enhanced ionic conductivity at intermediate temperatures are required. The bulk of the existing literature on high-temperature SOFCs has focussed on zirconia-based binary systems as electrolytes, due to their high ionic conductivity and negligible electronic conductivity. Only select compositions within the zirconia-scandia system have demonstrated acceptable ionic conductivity levels at intermediate temperatures; however unstable phase assemblage and the high economic cost of scandia are clear disadvantages. Ceria-based binary systems have demonstrated improved oxygen-ion conductivity at intermediate temperature compared to many zirconia systems, however significant levels of n-type electronic conductivity are observed at low oxygen partial pressures. Consequently it was thought unlikely that significant increases in ionic conductivity would be found in existing zirconia- and ceria-based binary systems, therefore another approach was required in an attempt to improve the performance of these established fluorite systems. The fluorite systems Zr0.75Ce0.08M0.17O1.92 (M = Nd, Sm, Gd, Dy, Ho, Y, Er, Yb, Sc) were prepared and investigated as possible, intermediate-temperature SOFC electrolytes in an attempt to combine the higher conductivity found in the ceria systems with the low electronic conductivity observed in the zirconia systems. Also it was anticipated that systems containing dopants not previously observed to confer high ionic conductivity in either zirconia- and ceria-based binary systems, might exhibit enhanced ionic conductivity with expansion of the zirconia lattice resulting from the addition of ceria. All the as-fired Zr0.75Ce0.08M0.17O1.92 compositions possessed the face-centred cubic structure and lattice parameter measurements revealed the anticipated unit cell enlargement as the size of the dopant cation increased. No unusual microstructural parameters were identified that could be expected to interfere with the ionic transport properties in the as-fired compositions. The electrical conductivity was found to be influenced by the dopant-ion radius, the presence of ceria, low oxygen partial pressures and, in some compositions, the formation of poorly conducting, ordered-pyrochlore microdomains dispersed amongst the cubic defect-fluorite matrix. In a second approach to the formulation of new oxygen-ion conductors suitable for the intermediate-temperature SOFC, compounds possessing structures other than the fluorite structure were considered. An examination of the literature for oxides having the pyrochlore, scheelite and perovskite structures showed that the Sr+2- and Mg+2-doped LaGaO3 perovskites (LSGM) possessed ionic conductivity equal to the highest conducting, zirconia and ceria binary compounds. Therefore the perovskite systems La0.9Sr0.1Ga(0.8-x)InxMg0.2O2.85 (X = 0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8) (I-LSGM) were prepared and examined, the objective being to favourably influence structural parameters believed responsible for optimal ionic conductivity, namely the unit cell symmetry and volume. It was found that In+3 systematically substituted for Ga+3 on to the B-site of LSGM at least up to the X = 0.4 composition. While In+3 was found to replace the Ga+3 as expected, Mg+2, which occupies the same crystallographic site, was also replaced by In+3. Up to the X = 0.2 composition, at least two trace level secondary phases were observed to form along with the bulk I-LSGM phase. For I-LSGM compositions with X > 0.2, significantly larger concentrations of the secondary phases were identified. Evidence of a strontium-rich, high-temperature liquid phase was observed also near the grain boundaries on as-sintered and thermally etched surfaces in LSGM and I-LSGM compositions. It is believed that the observed, high sintered density in the complex, doped-LaGaO3 systems is due to the formation of this high-temperature liquid phase. Increasing levels of diffuse scatter and superstructure formation were observed in electron diffraction patterns in the I-LSGM bulk phase (up to X = 0.2), indicating a possible decrease in vacancy concentration and reduced, localised unit cell symmetry. The electrical conductivity in the I-LSGM compositions was believed to be influenced by the distortion of the oxygen-ion conduction path, a reduction in vacancy concentration, formation of stronger dopant-vacancy associates at low temperature and the presence of ordered structures. In addition, phase instability, in the form of subtle ordering in specific crystalline planes, was observed to influence the electrical conductivity as a function of time at intermediate temperatures.
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Klarbring, Johan. "A first-principles non-equilibrium molecular dynamicsstudy of oxygen diffusion in Sm-doped ceria." Thesis, Linköpings universitet, Teoretisk Fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-118773.
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Solid oxide fuel cells are considered as one of the main alternatives for future sources of clean energy. To further improve their performance, theoretical methods able to describe the diffusion process in candidate electrolyte materials at finite temperatures are needed. The method of choice for simulating systems at finite temperature is molecular dynamics. However, if the forces are calculated directly from the Schrödinger equation (first-principles molecular dynamics) the computational expense is too high to allow long enough simulations to properly capture the diffusion process in most materials. This thesis introduces a method to deal with this problem using an external force field to speed up the diffusion process in the simulation. The method is applied to study the diffusion of oxygen ions in Sm-doped ceria, which has showed promise in its use as an electrolyte. Good agreement with experimental data is demonstrated, indicating high potential for future applications of the method.
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de, Carvalho Tomás Eduarda M. S. "Characterisation of the ceria and yttria co-doped scandia zirconia, produced by an innovative sol-gel and combustion process." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/931.
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In the last decade new materials appeared that are candidates to be used as an electrolyte in a Solid Oxide Fuel Cell, SOFC. Some materials show high ionic conductivity but lack in important properties, such as mechanical stability or chemical compatibility with other materials in the fuel cell. Scandia Stabilised Zirconia, SSZ, became a possibility when the scandia price dropped with the opening of the Chinese and Russian markets. In the starting system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2), scandia is introduced to improve conductivity and stabilise the cubic phase; yttria is introduced to fully stabilise the cubic phase and ceria to enhance conductivity lost with the introduction of yttria. The aim of this project is to develop a reliable new method to produce quality ceramics that are not strongly composition dependent, then to prepare a range of compositions and compare intrinsic properties without having to be concerned that poor sintering dominates conduction properties. This project can be divided in two sections, the first section the powder production method, the characteristics of the powders and its final products are in focus. In the second section the relation between electric characteristics and microstructure of the material is reported. In the first section, the effect of different compositions of the system Ce[subscript(x)]Y[subscript(0.2-x)]Sc₀.₆Zr₃.₂O[subscript(8-δ)], (0≤x≤0.2) is studied, in terms of structure, phase and microstructure. The nature, size and shape of the powders are discussed, and their effect on the final product. The sol-gel and combustion method gives the formation of hard agglomerates (shells), during the combustion, a wide range of grain sizes, between less than 1µm and 200 µm, and the formation of grains with non spherical shape. In this project, the sol-gel and combustion process and solid state method are also compared. In the second section of this project, AC Impedance measurements, as a function of temperature, oxygen partial pressure and time are discussed. The Arrhenius plot for all compositions shows two regions (high and low temperature) and the change of region occurs at 580 °C. At low temperatures there is a slight difference between compositions but this difference is less at high temperatures. The obtained ionic conductivity, at 350 °C, varies from 3.84×10⁻⁶ to 5.53×10⁻⁵ S/cm; at 700 °C, ionic conductivity from 0.013 to 0.044 S/cm. At low temperatures, the activation energy associated with bulk process is generally lower than grain boundary process; for example, the composition Ce₀.₁Y₀.₁Sc₀.₆Zr₃.₂O₇.₆₅ has an activation energy, for the bulk process, of 1.05 eV and an activation energy, for the grain boundary process, of 1.17 eV. For compositions with higher ceria content, activation energy, for bulk and grain boundary, have similar values. The AC impedance as function of oxygen partial pressure show that the amount of ceria introduced as an effect on the conductivity at low oxygen partial pressure. For the sample with no ceria in its composition, Y₀.₂Sc₀.₆Zr₃.₂O₇.₆₀, the conductivity does not vary significantly as the oxygen partial pressure is decreased; for oxygen partial of 0.21 atm, conductivity is 0.018 S/cm and when oxygen partial pressure is approximately 10⁻²⁴ atm conductivity is 0.018 S/cm. For the sample with a higher content of ceria, Ce₀.₁₂Y₀.₀₈Sc₀.₆Zr₃.₂O₇.₆₆, there is a decrease in conductivity while oxygen partial pressure decreases; and there is also the appearance of a semi-circle for lower oxygen partial pressures. For oxygen partial pressure approximately 0.21 atm, conductivity is 0.019 S/cm, but when oxygen partial pressure is decreased to 10⁻²⁴ atm conductivity decreases to 0.011 S/cm. AC impedance measurements as a function of annealing time at 600 °C were performed. Total conductivity is fairly stable, for all compositions, until 1800 hours but after this time, conductivity slowly decreases. Some compositions show a second semi-circle in the AC impedance spectra, either from the beginning, time equals 0 hours, or after some working hours. Here, the changes in conduction and conduction processes with time are discussed.
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Yang, Qigui. "Theoretical study of Gd2O3-CeO2 (111) interface." Thesis, KTH, Materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-234848.
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Atomistic modelling has widely been applied for studying structures and properties of materials. There are various methods to perform atomistic modelling. This master thesis presents a combined density functional theory (DFT) and cluster expansion (CE) study of Gd2O3 and Gd2O3-CeO2 interface (GCI) relevant for solid oxide fuel cells (SOFCs). The energy differences (ΔE) of Va-O exchanges in C-type Gd2O3 and at GCI are calculated using both DFT and CE methods. We also calculated the migration energy (Emig) of Va jumps in Gd2O3 and at GCI by DFT. The comparison between the CE and DFT results demonstrates that the CE method provides a relatively accurate estimation of ΔE while it requires less computational resources. Furthermore, the CE method is used to study the Va migration in the vicinity of the Gd2O3-CeO2 interface. The potential energy landscapes of different types of paths are studied.Atomistisk modellering har i stor utsträckning använts för att studera strukturer och egenskaper hos material. Det finns många olika metoder för att utföra atomistisk modellering. Detta masterprojekt presenterar en kombinerad density functional theory (DFT) och cluster expansion (CE) studie av Gd2O3- och Gd2O3-CeO2 gränssnittet (GCI), relevant för fastoxidbränsleceller (SOFC). Energiskillnaderna (ΔE) för Va-O-utbytet i C-typ Gd2O3 och vid GCI beräknas med användning av både DFT- och CE-metoder. Vi beräknade också migrationsenergin (Emig) av Va-hopp i Gd2O3 och vid GCI med DFT. Jämförelsen mellan CE och DFT-resultaten visar att CE-metoden ger en relativt noggrann uppskattning av ΔE samt att den kräver mindre beräkningsresurser. Vidare används CE-metoden för att studera Va- migrering i närheten av Gd2O3-CeO2-gränssnittet. Det potentiella energilandskapet för olika vägar studeras.
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Cella, Beatriz. "S?ntese e caracteriza??o de NiO-CGO para anodo e eletr?litos s?lidos e base de C?ria para SOFC." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12682.
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Previous issue date: 2009-01-04The direct use of natural gas makes the Solid Oxide Fuel Cell (SOFC) potentially more competitive with the current energy conversions technologies. The Intermediate Temperature SOFC (IT-SOFC) offer several advantages over the High Temperature SOFC (HT-SOFC), which includes better thermal compatibility among components, fast start with lower energy consumption, manufacture and operation cost reduction. The CeO2 based materials are alternatives to the Yttria Stabilized Zirconia (YSZ) to application in SOFC, as they have higher ionic conductivity and less ohmic losses comparing to YSZ, and they can operate at lower temperatures (500-800?C). Ceria has been doped with a variety of cations, although, the Gd3+ has the ionic radius closest to the ideal one to form solid solution. These electrolytes based in ceria require special electrodes with a higher performance and chemical and termomechanical compatibility. In this work compounds of gadolinia-doped ceria, Ce1-xGdxO2-δ (x = 0,1; 0,2 and 0,3), used as electrolytes, were synthesized by polymeric precursors method, Pechini, as well as the composite material NiO - Ce0,9Gd0,1O1,95, used as anode, also attained by oxide mixture method, mixturing the powders of the both phases calcinated already. The materials were characterized by X ray diffraction, dilatometry and scanning electronic microscopy. The refinement of the diffraction data indicated that all the Ce1-xGdxO2-δ powders were crystallized in a unique cubic phase with fluorite structure, and the composite synthesized by Pechini method produced smaller crystallite size in comparison with the same material attained by oxide mixture method. All the produced powders had nanometric characteristics. The composite produced by Pechini method has microstructural characteristics that can increase the triple phase boundaries (TPB) in the anode, improving the cell efficiency, as well as reducing the mass transport mechanism effect that provokes anode degradation
A utiliza??o direta do g?s natural torna a c?lula a combust?vel de ?xido s?lido (SOFC) potencialmente mais competitiva com as atuais tecnologias para convers?o de energia. A SOFC de temperatura intermedi?ria (IT-SOFC) oferece muitas vantagens sobre a SOFC de alta temperatura (HT-SOFC), que incluem melhor compatibilidade t?rmica entre os componentes, partida r?pida com menos consumo energ?tico, redu??o de custos de obten??o e opera??o. Os materiais baseados em CeO2 s?o alternativas aos eletr?litos de zirc?nia estabilizada com ?tria (YSZ) para aplica??es em SOFC, pois t?m condutividade i?nica maior e menores perdas ?hmicas em compara??o a YSZ, e podem operar a temperaturas mais baixas (500-800?C). C?ria tem sido dopada com uma variedade de c?tions, entretanto, o Gd3+ possui o raio i?nico mais pr?ximo do ideal para forma??o da solu??o s?lida. Esses eletr?litos baseados em c?rio requerem eletrodos especiais com um alto desempenho e compatibilidade termomec?nica e qu?mica. Neste trabalho compostos c?ria dopada com gadol?nia, Ce1-xGdxO2-δ (x = 0,1; 0,2 e 0,3), utilizadas como eletr?litos, foram sintetizados a partir do m?todo dos precursores polim?ricos, Pechini, assim como o material comp?sito NiO - Ce0,9Gd0,1O1,95, usado para anodo, obtido tamb?m pelo m?todo de mistura dos ?xidos, p?s das duas fases j? calcinadas. Os materiais foram caracterizados atrav?s das t?cnicas de difra??o de raios X, dilatometria e microscopia eletr?nica de varredura. O refinamento dos dados obtidos pela difra??o de raios X indicou que todos os p?s de Ce1-xGdxO2-δ cristalizaram em uma ?nica fase c?bica com estrutura fluorita, e que o comp?sito obtido por Pechini produziu menores tamanhos de cristalitos das fases em compara??o com o p? sintetizado por mistura de ?xidos em uma mesma temperatura de calcina??o. Todos os p?s obtidos t?m caracter?sticas nanom?tricas. O comp?sito obtido por Pechini possui caracter?sticas microestruturais que podem aumentar a fronteira de fase tripla (TPB) dentro do anodo, melhorando a efici?ncia da c?lula, assim como reduzir o efeito do mecanismo de transporte de massa que provoca degrada??o do anodo
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REIS, SHIRLEY L. dos. "Crescimento de graos e condutividade eletrica da ceria-samaria usando o metodo de sinterizacao e duas etapas." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9540.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Yue, Xiangling. "The development of alternative cathodes for high temperature solid oxide electrolysis cells." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/6531.
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This study mainly explores the development of alternative cathode materials for the electrochemical reduction of CO₂ by high temperature solid oxide electrolysis cells (HTSOECs), which operate in the reverse manner of solid oxide fuel cells (SOFCs). The conventional Ni-yttria stabilized zirconia (YSZ) cermets cathode suffered from coke formation, whereas the perovskite-type (La, Sr)(Cr, Mn)O₃ (LSCM) oxide material displayed excellent carbon resistance. Initial CO₂ electrolysis performance tests from different cathode materials prepared by screen-printing showed that LSCM based cathode performed poorer than Ni-YSZ cermets, due to non-optimized microstructure. Efforts were made on microstructure modification of LSCM based cathodes by means of various fabrication methods. Among the LSCM/YSZ graded cathode, extra catalyst (including Pd, Ni, CeO₂, and Pt) aided LSCM/GDC (Gd₀.₁Ce₀.₉O₁.₉₅) cathode, LSCM impregnated YSZ cathode, and GDC impregnated LSCM cathode, the GDC impregnated LSCM cathode, with porous LSCM as backbone for finely dispersed GDC nanoparticles, was found to possess the desired microstructure for CO₂ splitting reaction via SOEC. Incorporating of 0.5wt% Pd into GDC impregnated LSCM cathode gave rise to an Rp of 0.24 Ω cm² at open circuit voltage (OCV) at 900°C in CO₂-CO 70-30 mixture, comparable with the Ni/YSZ cermet cathode operated in the identical conditions. Meanwhile, the cathode kinetics and possible mechanisms of the electrochemical reduction of CO₂ were studied, and factors including CO₂/CO composition, operation temperature and potential were taken into account. The current-to-chemical efficiency of CO₂ electrolysis was evaluated with gas chromatography (GC). The high performance Pd and GDC co-impregnated LSCM cathode was also applied for CO₂ electrolysis without protective CO gas in feed. This cathode also displayed superb performance towards CO₂ electrochemical reduction under SOEC operation condition in CO₂/N₂ mixtures, though it had OCV as low as 0.12V at 900°C. The LSCM/GDC set of SOEC cathode materials were investigated in the application of steam electrolysis and H₂O-CO₂ co-electrolysis as well. For the former, adequate supply of steam was essential to avoid the appearance of S-shaped I-V curves and limited steam transport. The 0.5wt% Pd and GDC co-infiltrated LSCM material has been found to be a versatile cathode with high performance and good durability in SOEC operations.
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Medeiros, Amanda Lucena de. "Influ?ncia do m?todo de s?ntese e caracteriza??o de p?s comp?sitos de NiO- Ce1-xEuxO2-δ para anodos catal?ticos de c?lulas a combust?vel." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12795.
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Previous issue date: 2013-02-06Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
Fuel cells are electrochemical devices that convert chemical energy into electricity. Due to the development of new materials, fuel cells are emerging as generating clean energy generator. Among the types of fuel cells, categorized according to the electrode type, the solid oxide fuel cells (SOFC) stand out due to be the only device entirely made of solid particles. Beyond that, their operation temperature is relatively high (between 500 and 1000 ?C), allowing them to operate with high efficiency. Another aspect that promotes the use of SOFC over other cells is their ability to operate with different fuels. The CeO2 based materials doped with rare earth (TR+3) may be used as alternatives to traditional NiO-YSZ anodes as they have higher ionic conductivity and smaller ohmic losses compared to YSZ, and can operate at lower temperatures (500-800?C). In the composition of the anode, the concentration of NiO, acting as a catalyst in YSZ provides high electrical conductivity and high electrochemical activity of reactions, providing internal reform in the cell. In this work compounds of NiO - Ce1-xEuxO2-δ (x = 0.1, 0.2 and 0.3) were synthesized from polymeric precursor, Pechini, method of combustion and also by microwave-assisted hydrothermal method. The materials were characterized by the techniques of TG, TPR, XRD and FEG-SEM. The refinement of data obtained by X-ray diffraction showed that all powders of NiO - Cex-1EuxO2-δ crystallized in a cubic phase with fluorite structure, and also the presence of Ni. Through the characterizations can be proved that all routes of preparation used were effective for producing ceramics with characteristics suitable for application as SOFC anodes, but the microwave-assisted hydrothermal method showed a significant reduction in the average grain size and improved control of the compositions of the phases
C?lulas a combust?vel s?o dispositivos eletroqu?micos que convertem a energia qu?mica em el?trica. Em virtude do desenvolvimento de novos materiais, as c?lulas a combust?vel v?m se destacando como promissores na gera??o de energia de forma limpa. Dentre os tipos de c?lulas a combust?vel, classificadas de acordo com o tipo de eletr?lito, destacam-se as de ?xido s?lido (SOFC), por serem as ?nicas inteiramente constitu?das por s?lidos. Al?m disso, pela sua temperatura de opera??o ser relativamente elevada (entre 500 e 1000 ?C), estas c?lulas operam com alta efici?ncia. Outro aspecto que favorece o emprego de SOFC ? a sua habilidade de operar com diferentes combust?veis, como fontes de hidrog?nio.Os materiais a base de CeO2 dopados com terras raras (TR+3) podem ser utilizados como alternativas aos tradicionais anodos de NiO-YSZ. Al?m de maior condutividade i?nica maior e menores perdas ?hmicas, elas podem operar a temperaturas mais baixas (500- 800?C). Na composi??o do anodo, a concentra??o de NiO, atuando como catalisador confere alta condutividade el?trica e alta atividade eletroqu?mica das rea??es, proporcionando a reforma interna do combust?vel na c?lula. Neste trabalho compostos de NiO - Ce1-xEuxO2-δ (x = 0,1; 0,2 e 0,3), foram sintetizados a partir do m?todo dos precursores polim?ricos, Pechini, do m?todo de combust?o e, tamb?m, pelo m?todo hidrotermal assistido por micro-ondas. Os materiais obtidos foram caracterizados atrav?s das t?cnicas de TG, DRX, TPR e MEV-FEG. O refinamento dos dados obtidos pela difra??o de raios X indicou que todos os p?s de NiO - Ce1- xEuxO2-δ cristalizaram-se em uma fase c?bica com estrutura fluorita, e tamb?m a presen?a de NiO. Todas as rotas de prepara??o utilizadas mostraram-se eficientes para a produ??o de p?s com caracter?sticas adequadas para aplica??o como anodos de SOFC, por?m o m?todo hidrotermal assistido por micro-ondas apresentou significativa redu??o do tamanho m?dio de gr?os e melhor controle das composi??es das fases
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Li, Jia-Fu, and 李家府. "Study of Methane Reaction with Gadolinia-doped Ceria Mixed Bismuth Oxide." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/86607226157235212129.
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Chang, Jia-Yu, and 張家瑜. "Preparation of Gadolinia-doped Ceria Solid Electrolyte Materials by Atmospheric Pressure Plasma Jet." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/09848094310730501084.
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碩士國立臺灣科技大學
機械工程系
101
Gadolinia-doped ceria (GDC) materials are considered as electrolytes for the most potential to replace traditional yttria-stabilized zirconia (YSZ) in intermediate temperature solid oxide fuel cell (IT-SOFC). A novel atmospheric pressure plasma jet (APPJ) has been widely applied in industry due to its many advantages of operating in atmosphere, eliminating an expensive vacuum system, high efficiency, and low cost. This study is to evaluate the application of APPJ system to prepare GDC materials via the mixture solution of cerium nitrate hexahydrate (Ce(NO3)3．6H2O) and gadolinium nitrate hexahydrate (Gd(NO3)3．6H2O) as the precursor. In this study, the framework is primary divided into two parts. For the first part, Ar and O2 were used as the carrier gases to feed the precursor mist into the APPJ preparing GDC particles, respectively. Materials characteristics of GDC particles are investigated by X-ray diffraction (XRD), Raman spectrometer (Raman), field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), X-ray fluorescence spectroscopy (XRF) and X-ray photoelectron spectroscope (XPS). Using Ar as carrier gas, the partial reduction of GDC from Ce4+ to Ce3+ was observed during the plasma synthesis. For the case of O2 carrier gas, however, the main chemical structure of Ce4+ in GDC particles was obtained, which could improve the ionic conductivity of electrolytes. According to the size relationship of the atomized droplets and precursors and chemical reactions inside the plasma region at normal pressure, the one-step fabrication of formation mechanism for the prepared GDC particles was proposed in this study. Meanwhile, the results also demonstrated that the feasibility of preparation of well-crystallized GDC nanoparticles by APPJ system was successfully achieved in short time.
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Chen, Hsiao-Min, and 陳曉民. "A study of steam reforming of methanol over gadolinia-doped ceria supported Cu catalyst." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/69817844267219363070.
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Chuang, Yu-Han, and 莊玉涵. "Fabrication and Characterization of Gadolinia-doped Ceria Thin Electrolytes Deposited by RF Magnetron Sputtering." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/yz2qyr.
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碩士國立臺北科技大學
材料科學與工程研究所
97
The deposition and charterization of 10% Gd doped ceria(GDC10) film on Si substrate and NiO/GDC anode by sputtering wad studied because GDC exhibits an ionic conductivity which is 3-5 times higher than YSZ.The crystal structure, chemical composition, surface morphology and roughness of GDC films deposited with different gas flow rations. The film deposited on Si substrate and NiO/GDC which structure is different. And the deposited rate is slower than deposited on Si.We find the oxygen flow rate will effect the chemical composition. When oxygen flow rate is from 2 sccm to 10 sccm ,the composition will more closely NiO/GDC10.
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Chen, Yong-siou, and 陳永修. "Gadolinia-doped Ceria Solid Electrolyte Thin Films Prepared by RF Reactive Sputtering and Its Annealing Behavior." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/60673152149351808355.
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碩士國立臺灣科技大學
化學工程系
96
Abstract This study is to evaluate the feasibility and application of Gadolinia-doped Ceria (GDC) thin films as solid electrolyte for Solid Oxide Fuel Cells (SOFCs). GDC thin films were deposited on commercialized alumina substrates and NiO-GDC substrates by RF reactive sputtering in various O2/Ar flow ratio and then treated with the thermal treatments. Experiment results indicated that the deposition rate, surface morphology, crystalline structure, and ionic conductivity of the deposited films depend on the O2/Ar flow ratio and annealing temperatures. Our results showed the surface morphology of as-deposited GDC thin films were found to be an assembly of columnar crystallites and the crystalline structure was varied from incompletely-oxidized (Ce,Gd)Ox to completely-oxidized GDC as increasing the O2/Ar flow ratio. GDC thin films were cubic fluorite structure as the annealing temperature was 700°C, and surface morphology became denser as increasing upto 900°C. However, when the annealing temperature was raised up to 1100°C, cracks on the surface of GDC thin films were apparently observed because of the thermal expansion conefficient mismatch between GDC films and alumina substrate. The governing mechanism of conduction of annealed GDC thin films were mainly dominated by grain contribution at lower oxygen flow rate when the annealing temperature was 700°C, while the mechanism was gradually chaged to grain boundary contribution with deacresing the ionic conductivity at higher oxygen flow rate. At 900°C, the governing mechanism of conduction of annealed GDC thin films were changed to grain contribution with increasing the ionic conductivity. However, when the annealing temperature was raised to 1100°C, the governing mechanism of conduction of annealed GDC thin films were changed to grain boundary contribution with the lower ionic conductivity because of the existence of the cracks on surface. Keywords：Solid Oxide Fuel Cells (SOFCs), Gadolinia-doped Ceria (GDC), RF reactive sputtering
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Wang, Chun-Hsiu, and 王俊修. "Study of Self Decoking over Gadolinia-doped Ceria Supported Ni and Fe Catalysts after Methane Reaction." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/70277547372887585242.
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Chien, Ching-Hung, and 錢景鴻. "Preparation of multi-element doped ceria electrolyte for intermediate temperature solid oxide fuel cell." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/p6xv32.
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碩士國立臺北科技大學
材料科學與工程研究所
105
In this study, Ce0.8A0.2O2–δ (A = Sm, Nd), (La0.77Sr0.2B0.03)xCe1–xO2–δ (B = Ca, Ba and x = 0.15, 0.2), and Ce0.8Nd0.2–yCyO2–δ (C = Y, Ca and y = 0.02, 0.03) intermediate temperature solid fuel cell (IT-SOFC) electrolytes were synthesized by solid state reaction method. The effects of different holding temperature on the electrical and microstructure were investigated. The crystal structure, microstructure and ion conductivity of the specimen were analyzed by XRD, SEM, Raman spectroscopy, high analytical electron spectroscopy, DC power and AC impedance and electrochemical workstation. The results showed that after sintered at 1500 °C for 4 hrs, the electrolyte specimen have controlled specific surface area with very less porosity which is need for electrolyte material, and no secondary phase formation. It can be verified as a cubic fluorite structure phase. By the reductive reaction of Ce4+ to Ce3+, the oxygen vacancies increase as the sample is treated in the reducing atmosphere. As the sintering temperature increases, the conductivity of the electrolyte specimen were increased. Through the DC and AC conductivity measurement, the SDC20-4, LSB20DC-4, LSC15DC-4, N18C02DC−4, and N17C03DC-4 samples have better conductivity at 800 °C. For the preformation of the cell, the results show that the N17C03DC-4 had the highest maximum power density (266 mW / cm2) and the lowest ASRTotal value at 800 °C.
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Santos, Tiago Henrique Silva. "Development of Sm-/Pr-doped ceria materials for electrolyte applications in Solid Oxide Cells." Dissertação, 2018. https://hdl.handle.net/10216/111632.
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Santos, Tiago Henrique Silva. "Development of Sm-/Pr-doped ceria materials for electrolyte applications in Solid Oxide Cells." Master's thesis, 2018. https://hdl.handle.net/10216/111632.
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Wu, Chih-Hsuan, and 吳至璿. "Electrochemical performance of Gd-doped ceria interlayer on the solid oxide fuel cell and solid oxide electrolysis cell." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/97721891665094352738.
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碩士元智大學
機械工程學系
105
A procedure is mainly study the intermediate temperature solid oxide fuel cell (IT-SOFC), and further develop it into Utilized Regenerative solid oxide fuel cell (URSOFC), which has the capability of SOFC and SOEC bidirectional mode. In this study, an anode supported button cell was prepared by TLC method. The anode material was porous nickel oxide (NiO-YSZ) and lanthanum strontium cobalt ferrite (LSCF) was used as the cathode material. The lanthanum strontium cobalt ferrite is a mixed ionic electronic conductor with respect to the lanthanum strontium manganese (LSM) with higher electrical conductivity and good ionic conductivity. But at high temperatures with the electrolyte YSZ produce non-conductive phase such as: La2Zr2O7、SrZrO3. In order to avoid this phenomenon, we devoted to study of GDC interlayer sintering process, and GDC interlayer sintered between 1200-1300 degrees. And test at 700-850 degrees to know the chemical performance. We used SEM to know the cell microstructure changed after SOFC mode and SOEC mode. Finally, we found that the GDC interlayer sintered at 1300 degrees had a maximum power density of 288.578 (mW/cm2) at operation temperature 850 °C. And one of the biggest increases in performance is the GDC interlayer sintered at 1250 degrees with a maximum current density 648.464 (mA / cm2) at 2.0 V at 850 °C. Compared to traditional SOFC, electrolysis performance will get 386% performance improvement.
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Ismail, Mazni. "Model Development and Validation of Samaria Doped Ceria (SDC) Based Solid Oxide Fuel Cell Operating with Practical Fuels." Thesis, 2013. http://hdl.handle.net/10012/7898.
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Solid Oxide Fuel Cell (SOFC) is a promising technology for producing electricity cleanly and efficiently. This type of fuel cell is a high temperature fuel cell operating around 1000C for state-of-the-art SOFC. An advantage of the high temperature is the possibility of combined heat and power generation which would even further increase the efficiency of this technology. However, due to high operating temperatures, there are problems associated with the development and commercialization of SOFC, such as requirement of high temperature gas seals, and relatively poor long-term stability. The current trend in SOFC development is therefore to reduce the operating temperature of the cell to the range 600-800°C. However, this requires developing new cell designs and materials since decreasing the operating temperature increases the ohmic overpotential due to higher ionic diffusion resistance in the electrolyte, thereby reducing electrochemical performance. For intermediate temperature SOFC, SDC is a promising electrolyte material to reduce the ohmic overpotential.
The present research focused on developing a 1D model of SDC based SOFC validated for a number of feed gas compositions, from humidified H2, mixture of CO and CO2, to several syngas compositions (typical of diesel syngas, biomass syngas and pre-reformed natural gas). The model was developed for an anode supported cell. Few parameters were used as free fit parameters: essentially structural parameters, such as porosity and tortuosity, as well as kinetic parameters for H2 and CO electrochemical reactions. In most cases, the simulated results (polarization curve) fitted well the experimental data. It was seen that the performance of CO/CO2 system is considerably lower than the H2/H2O system. The model results also allowed to access variables’ profiles that would not be accessible experimentally, such species composition profile and local current density along the anode. In particular, it was observed that most the electrochemical reaction occurred within 10 m away from the anode/electrolyte interface.
In the literature, the water-gas shift (WGS) reaction is considered to occur only over Ni, but the present work demonstrated that SDC is active toward the WGS reaction. Therefore, a kinetic study was carried out to determine a rate expression for the WGS reaction. This rate expression was then incorporated into the SOFC model. The results indicated that inclusion of the WGS reaction on SDC has minor or negligible effect in most situations, except in the case of CO mole fraction for the diesel syngas feed at higher cell voltage. The reason was that the composition of diesel syngas was such that there was a higher driving force for the WGS reaction to proceed in the reverse WGS direction. When the water content is high enough, as in the case of higher current densities, the form of the derived rate expression for the WGS on SDC makes the value of this rate very small. The rate expression was derived using relatively small amounts of water because of experimental limitation and therefore, the form of this rate needs to be revisited by considering higher amount of water.
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"Optimization of Ionic Conductivity in Doped Ceria Using Density Functional Theory and Kinetic Lattice Monte Carlo." Doctoral diss., 2011. http://hdl.handle.net/2286/R.I.9006.
Full textAbstract:
abstract: Fuel cells, particularly solid oxide fuel cells (SOFC), are important for the future of greener and more efficient energy sources. Although SOFCs have been in existence for over fifty years, they have not been deployed extensively because they need to be operated at a high temperature (∼1000 °C), are expensive, and have slow response to changes in energy demands. One important need for commercialization of SOFCs is a lowering of their operating temperature, which requires an electrolyte that can operate at lower temperatures. Doped ceria is one such candidate. For this dissertation work I have studied different types of doped ceria to understand the mechanism of oxygen vacancy diffusion through the bulk. Doped ceria is important because they have high ionic conductivities thus making them attractive candidates for the electrolytes of solid oxide fuel cells. In particular, I have studied how the ionic conductivities are improved in these doped materials by studying the oxygen-vacancy formations and migrations. In this dissertation I describe the application of density functional theory (DFT) and Kinetic Lattice Monte Carlo (KLMC) simulations to calculate the vacancy diffusion and ionic conductivities in doped ceria. The dopants used are praseodymium (Pr), gadolinium (Gd), and neodymium (Nd), all belonging to the lanthanide series. The activation energies for vacancy migration between different nearest neighbor (relative to the dopant) positions were calculated using the commercial DFT code VASP (Vienna Ab-initio Simulation Package). These activation energies were then used as inputs to the KLMC code that I co-developed. The KLMC code was run for different temperatures (673 K to 1073 K) and for different dopant concentrations (0 to 40%). These simulations have resulted in the prediction of dopant concentrations for maximum ionic conductivity at a given temperature.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2011
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Kimpton, Justin Andrew. "Conductivity and microstructural characterisation of doped Zirconia-Ceria and Lanthanum Gallate electrolytes for the intermediate-temperature, solid oxide fuel cell /." 2002. http://adt.lib.swin.edu.au/public/adt-VSWT20060523.090655.
Full textAbstract:
Thesis (Ph.D.) - School of Engineering and Science, Swinburne University of Technology, 2002.Submitted in fulfillment of the requirements for the degree of Doctor of Philosophy, School of Engineering and Science, Swinburne University of Technology, 2002. Typescript. Includes bibliographical references (p. 229-239).
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Jung, Guo-Bin, and 鐘國濱. "Preparation of Samarium Doped Ceria as Solid Oxide Fuel Cell Electrolyte by Modified Sol-Gel Method and Study of its'' Conductivity." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/06248752952183062781.
Full textAbstract:
博士國立清華大學
化學工程學系
89
Doped ceria is difficult to sinter, at temperature required for SOFC (Solid Oxide Fuel Cell) fabrication, to near-full density ceramics. The development of doped ceria powders capable of sintering to full density below 1400℃ is important to facilitate SOFC fabrication. 20% samarium-doped ceria powders were prepared by the sol-gel method with different processes. The characteristic of the samples was investigated by particle size distribution, X-ray diffraction, crystallite size, and density result. A modified process with sol-gel method we first proposed involving high-carbon alcohol (long chain, high boiling point) distillation of molecular water yields soft-agglomerated nanocrystalline powders are easily sintered in air to yield near-fully relative density at 1300℃ for five hours (the lowest temperature as we know to synthesize doped ceria with high density), which is significantly lower than that for 1400-1500℃ required by the sol-gel method and much lower than that for 1600-1700℃ required by the solid state techniques. Conductivity, σ, of the samaria-doped ceria electrolyte is studied as a function of temperature and dopant concentration, x, which was from 5 to 30 mole%. It is shown that a maximum in σ versus x corresponds to a minimum in activation energy. It is found that the conductivity is completely due to oxygen vacancy conduction. The conductivity increases with increasing samaria doping and reaches a maximum for (CeO2)0.8(SmO1.5)0.2, which has a conductivity of 5.6×10-1 S/cm at 800℃. A curvature at T = Tc, the critical temperature, has been observed in the Arrhenius plot. This phenomenon may be explained by a model which proposed that, below Tc, nucleation of mobile oxygen vacancies into ordered clusters occurs, and, above Tc, all oxygen vacancies appear to be mobile without interaction with dopant cation. In addition, the composition dependences of both the critical temperature and the trapping energy consist with that of the activation energy. The overall resistivity of polycrystalline Sm0.2Ce0.8O1.9 obtained by DC four-probe method was found to increase linearly with the reciprocal of the average grain size ( ) at sintering temperature of 1500℃, and the grain resistivity can be got by extended the fitting line to . In addition, we found that by lowering the sintering temperature to 1100-1200℃, the overall resistivity decreases obviously and nearly equal to the grain resistivity obtained at 1500℃ which enable Sm0.2Ce0.8O1.9 working as SOFCs'' electrolyte at temperature lower than 700℃comparable to 800℃ traditionally sintering at 1500℃ or above. AC impedance spectroscopy has been used to separate grain and apparent grain boundary resistivity in a series of measurements on Sm0.2Ce0.8O1.9 ceramic electrolytes with a range of different grain size distributions. The "brick layer" microstructural model has been used to provide an estimate of apparent grain boundary resistivity and to relate the electrical properties of the ceramic to microstructural parameters. For samples sintering at 1500℃, a clear relationship between apparent grain boundary resistivity and the grain size corresponding to the result from the DC measurement. For samples sintering at 1100-1200℃, true grain boundary resistivity was nearly two order lower than that sintering at 1500℃ resulted from lower charge density of Sm''Ce in space charge layer around the grain boundary which will make the oxygen vacancy pass across with less activation energy. According to space charge theory, the grain boundary interface would carry an electrical potential resulted from the presence of excess ion of one sign, this will be compensated by a space-charge potential with the opposite sign adjacent to the grain boundary. Owing to the highly disordered structure of the grain boundary interface, the oxygen vacancy transport resistance at interface is negligible to that at space charge layer. Therefore, the intrinsic grain boundary resistivity of Samarium doping ceria is resulted from oxygen vacancy trapping with Sm''Ce in the space charge layer and a simple space charge density model was developed. In this model, we predicted that the Sm''Ce charge density increases with increasing sintering temperature and this will result in the higher probability to form complex for transporting oxygen vacancy. This is confirmed with the higher grain boundary resistivity resulted from higher activation energy. In addition, by lowering the sintering temperature, the grain resistivity decreases obviously compared to those sintering at high temperature, especially for ceria doped with small amount of samarium. The reason is that insufficient energy to derive the components within the grain diffuse completely therefore resulted in not well-distributed composition. As oxygen vacancy passes through, it chooses the environment with less resistance, and this will lowering the grain resistivity.
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Lyu, Yang-Ru, and 呂泱儒. "The Study of Yttria Doped Ceria/Nickel Oxide (YDC/NiO) Composite Powder Prepared by Spray Pyrolysis and its Applications to Solid-State Electrolyte." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/02077592243467964059.
Full textAbstract:
碩士逢甲大學
材料科學所
95
To investigate the effects of nickel diffusion on the characteristics and conduction behaviors of the electrolyte in solid oxide fuel cell (SOFC) during high operating temperature, cerium acetate hydrate, yttrium acetate hydrate and nickel acetate tetrahydrate were used as the precursors for preparing the 10 mole% yttria-doped ceria / nickel oxide (10YDC/NiO) ceramic composite powders by spray pyrolysis (SP) in the present study. The resulting powders were then collected by an electrostatic deposition technique (ESD). The results showed the obtained particle size distributed in a specific range depending on the collection voltage and particle size, whereas, revealed to be independent of the composition of the powders. Moreover, the SP particles showed to be hollow in shape with nanocrystalline structures and the surfaces on the particles are revealed to be shrunk and shriveled. The investigation of focus ion beam (FIB) and high resolution transmission electron microscopy (HRTEM) indicated the formation behavior of the particles to be the surface precipitation mechanism of the precursors. The difference in solubility of the precursors in water leaded the nickel oxide and YDC to precipitate respectively at inner and outer of the particles shell. After die-pressing and sintering, the presence of the pores resulted in poor electric properties of the bulk structure. The synchrotron X-ray absorption spectra for Ni LII, LIII -edge revealed that the nickel had a valence of +2 in the sintered composite. From the results of field emission scanning electron microscope (FESEM) and electron probe micro-analyzer (EPMA), nickel oxide tended to segregate or precipitate along/on the grain boundaries of YDC matrix. The AC impedance data showed that the grain-boundary conductivity of the 10YDC/NiO electrolyte increased with increasing the nickel-oxide content. Such the increasing ratio was proportional to the nickel-oxide content. In the meantime, the activation energy for grain boundary conduction tended to be reduced.
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Lim, Wendy. "MECHANICAL PROPERTIES OF Sc₀․₁Ce₀․₀₁Zr₀․₈₉O₂ ELECTROLYTE MATERIAL FOR INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS." 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-12-7567.
Full textAbstract:
Scandia doped zirconia has been considered a candidate for electrolyte material in intermediate temperature Solid Oxide Fuel Cells (SOFCs) due to its high ionic conductivity, chemical stability and good electrochemical performance. The aim of this study is to determine the mechanical properties of SCZ, ie. zirconia (ZrO₂) doped with Scandia (Sc₂O₃) and small amount of ceria (CeO₂) that are important for reliability and durability of the components manufactured from SCZ.
The SCZ was prepared from powder by uniaxiall cold pressing at subsequent sintering at 1550 ºC for 4 hours. The density and porosity of the sintered samples was measured following the ASTM Standard C20-00 for alcohol immersion method. A pure cubic phase of SCZ sample was identified by X-ray diffraction (XRD) at room temperature. Quantitative compositional analyses for Zr, Sc, Ce, Hf and Ti were carried out on a Cameca SX50 electron microprobe with wavelength-dispersive spectroscopy (WDS) and energy-dispersive spectroscopy (EDS). Scanning Electron Microscopy (SEM) images were acquired using both secondary electron (SE) and back-scattered electron (BSE) detectors. WDS and EDS analysis also revealed that Zr, Sc, Ce, Hf and Ti are relatively homogeneously distributed in the structure. The average grain size of sintered SCZ samples was measured to be 4 μm.
Thermal expansion at different temperatures for the SCZ ceramic was determined using Thermal Mechanical Analyzer, and the instantaneous Coefficient of Thermal Expansion (CTE) was found to be 8.726х10⁻⁶ 1/°C in the in 25-400 °C temperature range. CTE increases monotonically with temperature above 400 ºC to 1.16х10⁻⁵ at 890 °C, most likely as a result of thermo-chemical expansion due to an increase in oxygen vacancy concentration. Room temperature Vickers hardens of 12.5 GPa was measured at loads of 1000 g, while indentation fracture toughness was found to vary from 2.25 to 4.29 MPa m¹⁄², depending on the methodology that was used to calculate fracture toughness from the length of the median corner cracks.
Elastic moduli, namely Young and shear moduli were determined using Resonance Ultrasound Spectroscopy (RUS). It was found that elastic moduli decreases with temperature in non-linear manner, with significant drop in the 300-600 °C temperature range, the same temperature range in which loss modulus determined by Dynamic Mechanical Analyzer exhibits frequency dependant peaks. The high loss modulus and significant drop in elastic moduli in that temperature regime is attributed to the relaxation of doping cation-oxygen vacancies clusters.
The flexural strength in 4-point bending was measured at room temperature, 400 °C, 600 °C and 800 °C. and the results were analyzed using Weibull statistics. It was found that flexural strength changes with temperature in a sigmoidal way, with the minimum strength at around 600 °C. Non-linear decrease in strength with temperature can be traced back to the changes in elastic moduli that are caused predominately by relaxation of oxygen vacancies.