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Henson, Luke John. "Solid oxide fuel cells." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610397.
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Preece, John Christopher. "Oxygenated hydrocarbon fuels for solid oxide fuel cells." Thesis, University of Birmingham, 2006. http://etheses.bham.ac.uk//id/eprint/117/.
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In order to mitigate the effects of climate change and reduce dependence on fossil fuels, carbon-neutral methods of electricity generation are required. Solid oxide fuel cells (SOFCs) have the potential to operate at high efficiencies, while liquid hydrocarbon fuels require little or no new infrastructure and can be manufactured sustainably. Using hydrocarbons in SOFCs introduces the problem of carbon deposition, which can be reduced or eliminated by judicious choice of the SOFC materials, the operating conditions or the fuel itself. The aim of this project was to investigate the relationships between fuel composition and SOFC performance, and thus to formulate fuels which would perform well independent of catalyst or operating conditions. Three principal hypotheses were studied. Any SOFC fuel has to be oxidised, and for hydrocarbons both carbon-oxygen and hydrogen-oxygen bonds have to be formed. Oxygenated fuels contain these bonds already (for example, alcohols and carboxylic acids), and so may react more easily. Higher hydrocarbons are known to deposit carbon readily, which may be due to a tendency to decompose through the breaking of a C-C bond. Removing C-C bonds from a molecule (for example, ethers and amides) may reduce this tendency. Fuels are typically diluted with water, which improves reforming but reduces the energy density. If an oxidising agent could also act as a fuel, then overall efficiency would improve. Various fuels, with carbon content ranging from one to four atoms per molecule, were used in microtubular SOFCs. To investigate the effect of oxygenation level, alcohols and and carboxylic acids were compared. The equivalent ethers, esters and amides were also tested to eliminate carbon-carbon bonding. Some fuels were then mixed with methanoic acid to improve energy density. Exhaust gases were analysed with mass spectrometry, electrical performance with a datalogging potentiostat and carbon deposition rates with temperature-programmed oxidation. It was found that oxygenating a fuel improves reforming and reduces the rate of carbon deposition through a favourable route to CO/CO2. Eliminating carbon-carbon bonds from a molecule also reduces carbon deposition. The principal advantage of blending with methanoic acid was the ability to formulate a single phase fuel with molecules previously immiscible with water.
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Pramuanjaroenkij, Anchasa. "Mathematical Analysis of Planar Solid Oxide Fuel Cells." Scholarly Repository, 2009. http://scholarlyrepository.miami.edu/oa_dissertations/234.
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The mathematical analysis has been developed by using finite volume method, experimental data from literatures, and solving numerically to predict solid oxide fuel cell performances with different operating conditions and different material properties. The in-house program presents flow fields, temperature distributions, and performance predictions of typical solid oxide fuel cells operating at different temperatures, 1000 C, 800 C, 600 C, and 500 C, and different electrolyte materials, Yttria-Stabilized zirconia (YSZ) and Gadolinia-doped ceria (CGO). From performance predictions show that the performance of an anode-supported planar SOFC is better than that of an electrolyte-supported planar SOFC for the same material used, same electrode electrochemical considerations, and same operating conditions. The anode-supported solid oxide fuel cells can be used to give the high power density in the higher current density range than the electrolyte-supported solid oxide fuel cells. Even though the electrolyte-supported solid oxide fuel cells give the lower power density and can operate in the lower current density range but they can be used as a small power generator which is portable and provide low power. Furthermore, it is shown that the effect of the electrolyte materials plays important roles to the performance predictions. This should be noted that performance comparisons are obtained by using the same electrode materials. The YSZ-electrolyte solid oxide fuel cells in this work show higher performance than the CGO-electrolyte solid oxide fuel cells when SOFCs operate above 756 C. On the other hand, when CGO based SOFCs operate under 756 C, they shows higher performance than YSZ based SOFCs because the conductivity values of CGO are higher than that of YSZ temperatures lower than 756 C. Since the CGO conductivity in this work is high and the effects of different electrode materials, they can be implied that conductivity values of electrolyte and electrode materials have to be improved.
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Lee, Won Yong S. M. Massachusetts Institute of Technology. "Modeling of solid oxide fuel cells." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38564.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (p. 107-110).
A comprehensive membrane-electrode assembly (MEA) model of Solid Oxide Fuel Cell (SOFC)s is developed to investigate the effect of various design and operating conditions on the cell performance and to examine the underlying mechanisms that govern their performance. We review and compare the current modeling methodologies, and develop an one-dimensional MEA model based on a comprehensive approach that include the dusty-gas model (DGM) for gas transport in the porous electrodes, the detailed heterogeneous elementary reaction kinetics for the thermo-chemistry in the anode, and the detailed electrode kinetics for the electrochemistry at the triple-phase boundary. With regard to the DGM, we corrected the Knudsen diffusion coefficient in the previous model developed by Multidisciplinary University Research Initiative. Further, we formulate the conservation equations in the unsteady form, allowing for analyzing the response of the MEA to imposed dynamics. As for the electrochemistry model, we additionally analyzed all the possibilities of the rate-limiting reaction and proposed rate-limiting switched mechanism. Our model prediction agrees with experimental results significantly better than previous models, especially at high current density.
by Won Yong Lee.
S.M.
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Mirzababaei, Jelvehnaz. "Solid Oxide Fuel Cells with Methane and Fe/Ti Oxide Fuels." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1415461807.
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Chien, Chang-Yin. "Methane and Solid Carbon Based Solid Oxide Fuel Cells." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1299670407.
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Simo, Frantisek. "Novel oxide materials for solid oxide fuel cells applications." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/19353/.
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The work of this thesis focuses on three perovskite-based compounds: YSr2Cu3−xCoxO7+δ cuprates, Gd2BaCo2O5+δ related phases and Sr2SnO4 Ruddlesden-Popper structures. Both YSr2Cu3−xCoxO7+δ and Gd2BaCo2O5+δ are cathode material candidates for solid oxide fuel cells (SOFCs). Doping of Sr2SnO4 aims to enhance the ionic conductivity of the parent phase and explore the phases as a potential SOFCs electrolyte material. The cobalt content in the layered perovskite YSr2Cu3−xCoxO7+δ has been increased to a maximum of x = 1.3. A slight excess of strontium was required for phase purity in these phases, yielding the composition Y1−ySr2+yCu3−xCoxO7+δ (where y = 0.03 and 0.05). The potential of Y1−ySr2+yCu3−xCoxO7+δ (where x = 1 to 1.3) as a cathode material for a solid oxide fuel cell has been explored through optimisation of processing parameters, AC impedance spectroscopy and DC conductivity measurements. The stability of Y0.95Sr2.05Cu1.7Co1.3O7+δ with commercial electrolytes has been tested along with the stability under CO2. This material exhibits a significant improvement in properties compared to the parent member, Y0.97Sr2.03Cu2CoO7+δ, and is compatible with commercially available doped ceria electrolytes at 900 °C. Energetics of Ln2BaCo2O7 (Ln = Gd, Nd, Ce) materials consisting of a layer of LnBaCo2O5+δ (Ln = Gd, Nd) and a fluorite layer (CeO2 or Ln2O3, Ln = Gd, Nd) have been studied using DFT calculations. Various reactions including binary oxides and double perovskites were taken into an account for the formation energy calculations. Phases favourable in DFT calculations were observed also in PXRD patterns of the materials prepared by a solid state synthesis. DFT prediction has been also used in the work with Ruddlesden-Popper phases. The structures of experimentally prepared Nb- and Ta-doped Sr2SnO4 phases were investigated using high resolution diffraction methods. The conductivity of single phased materials was studied by AC impedance spectroscopy. A significant improvement in conductivity was observed in Sr2Sn1−xTaxO4 compounds with x = 0.03 and 0.04. The origin of the enhancement has been studied using different techniques such as solid state Sn-NMR, UV-vis and NIR spectroscopy methods and it tends to be explained by an ionic contribution.
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Nelson, George Joseph. "Solid Oxide Cell Constriction Resistance Effects." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10563.
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Solid oxide cells are best known in the energy sector as novel power generation devices through solid oxide fuel cells (SOFCs), which enable the direct conversion of chemical energy to electrical energy and result in high efficiency power generation. However, solid oxide electrolysis cells (SOECs) are receiving increased attention as a hydrogen production technology through high temperature electrolysis applications. The development of higher fidelity methods for modeling transport phenomena within solid oxide cells is necessary for the advancement of these key technologies. The proposed thesis analyzes the increased transport path lengths caused by constriction resistance effects in prevalent solid oxide cell designs. Such effects are so named because they arise from reductions in active transport area.
Constriction resistance effects of SOFC geometry on continuum level mass and electronic transport through SOFC anodes are simulated. These effects are explored via analytic solutions of the Laplace equation with model verification achieved by computational methods such as finite element analysis (FEA). Parametric studies of cell geometry and fuel stream composition are performed based upon the models developed. These studies reveal a competition of losses present between mass and electronic transport losses and demonstrate the benefits of smaller SOFC unit cell geometry. Furthermore, the models developed for SOFC transport phenomena are applied toward the analysis of SOECs. The resulting parametric studies demonstrate that geometric configurations that demonstrate enhanced performance within SOFC operation also demonstrate enhanced performance within SOEC operation.
Secondarily, the electrochemical degradation of SOFCs is explored with respect to delamination cracking phenomena about and within the critical electrolyte-anode interface. For thin electrolytes, constriction resistance effects may lead to the loss of electro-active area at both anode-electrolyte and cathode-electrolyte interfaces. This effect (referred to as masking) results in regions of unutilized electrolyte cross-sectional area, which can be a critical performance hindrance. Again analytic and computational means are employed in analyzing such degradation issues.
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Johnson, Janine B. "Fracture Failure of Solid Oxide Fuel Cells." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4847.
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Among all existing fuel cell technologies, the planar solid oxide fuel cell (SOFC) is the most promising one for high power density applications. A planar SOFC consists of two porous ceramic layers (the anode and cathode) through which flows the fuel and oxidant. These ceramic layers are bonded to a solid electrolyte layer to form a tri-layer structure called PEN (positive-electrolyte-negative) across which the electrochemical reactions take place to generate electricity. Because SOFCs operate at high temperatures, the cell components (e.g., PEN and seals) are subjected to harsh environments and severe thermomechanical residual stresses. It has been reported repeatedly that, under combined thermomechanical, electrical and chemical driving forces, catastrophic failure often occurs suddenly due to material fracture or loss of adhesion at the material interfaces. Unfortunately, there have been very few thermomechanical modeling techniques that can be used for assessing the reliability and durability of SOFCs. Therefore, modeling techniques and simulation tools applicable to SOFC will need to be developed. Such techniques and tools enable us to analyze new cell designs, evaluate the performance of new materials, virtually simulate new stack configurations, as well as to assess the reliability and durability of stacks in operation.
This research focuses on developing computational techniques for modeling fracture failure in SOFCs. The objectives are to investigate the failure modes and failure mechanisms due to fracture, and to develop a finite element based computational method to analyze and simulate fracture and crack growth in SOFCs. By using the commercial finite element software, ANSYS, as the basic computational tool, a MatLab based program has been developed. This MatLab program takes the displacement solutions from ANSYS as input to compute fracture parameters. The individual stress intensity factors are obtained by using the volume integrals in conjunction with the interaction integral technique. The software code developed here is the first of its kind capable of calculating stress intensity factors for three-dimensional cracks of curved front experiencing both mechanical and non-uniform temperature loading conditions. These results provide new scientific and engineering knowledge on SOFC failure, and enable us to analyze the performance, operations, and life characteristics of SOFCs.
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Sun, Baoguo. "Thermal Cycling of Solid Oxide Fuel Cells." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486561.
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Solid-oxide fuel cells (SOFCs) are energy conversion devices that theoretically have the capability of producing electrical- energy for as long as the fuel and oxidant are supplied to the electrodes and perfonnance is expected for at least 40,000 hours. However, it is observed that perfonnance degrades under repeated thennal cycling conditions, which limits the practicaI.operating life of these SOFCs. Therefore, the mechanism of damage to planar and integrated planar SOFCs (IPt' SOFCs) on thennal cycling is the subject of this thesis. A detailed literature review has been carried out and a mechanical and thennal properties database of the key materials used in these SOFCs has been built up. Extensive work has been done on the residual ~tress analysis of anode-supported and inert substrate supported SOFCs. Analytical model, surface profile measurement (Talysurf) and XRD stress analysis were used to detennine t4e residual stresses in the components. From this study, it was found that the difference of thennal expansion coefficients between components in the SOFCs is the dominant source of stress during thennal cycling in the absence of significant temperature gradient. For the integrated planar SOFCs, it was found tha~ the cells degraded due to the failure of the sealing materials during cooling. For anode supported planar SOFCs, the electrolyte (YSZ) is under high compressive stress when cooling from sintering or operating temperature to room temperature and the anode is under very small tensile stress. The results from theoretical analysis, XRD stress measurement and literature were compared and found that they agreed with each other quite well.
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Thomas, Martin Lutz Reiner. "Multiscale Simulations of Solid Oxide Fuel Cells." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534443.
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Torres-Caceres, Jonathan. "Manufacturing of Single Solid Oxide Fuel Cells." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5875.
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Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable. The goal of the research is to optimize and simplify the production of single SOFCs using high performance ceramics. This includes the use of 8mol% Y2O3-ZrO2 (YSZ) and 10mol% Sc2O3-1mol%CeO2-ZrO2 (SCSZ) layered electrolytes which purport higher conductivity than traditional pure YSZ electrolytes. Prior to printing the electrodes onto the electrolyte, the cathode side of the electrolyte was coated with 20mol% Gd2O3-CeO2 (GDC). The GDC coating prevents the formation of a nonconductive La2Zr2O7 pyrochlore layer, which forms due to the interdiffusion of the YSZ electrolyte ceramic and the (La0.6Sr0.4)0.995Fe0.8Co0.2O3 (LSCF) cathode ceramic during sintering. The GDC layer was deposited by spin coating a suspension of 10wt% GDC in ethanol onto the electrolyte. Variation of parameters such as time, speed, and ramp rate were tested. Deposition of the electrodes onto the electrolyte surface was done by screen printing. Ink was produced using a three roll mill from a mixture of ceramic electrode powder, terpineol, and a pore former. The pore former was selected based on its ability to form a uniform well-connected pore matrix within the anode samples that were pressed and sintered. Ink development involved the production of different ratios of powder-to-terpineol inks to vary the viscosity. The different inks were used to print electrodes onto the electrolytes to gauge print quality and consistency. Cells were produced with varying numbers of layers of prints to achieve a desirable thickness. Finally, the densification behaviors of the major materials used to produce the single cells were studied to determine the temperatures at which each component needs to be sintered to achieve the desired density and to determine the order of electrode application, so as to avoid over-densification of the electrodes. Complete cells were tested at the National Energy Technology Laboratory in Morgantown, WV. Cells were tested in a custom-built test stand under constant voltage at 800°C with 3% humidified hydrogen as the fuel. Both voltage-current response and impedance spectroscopy tests were conducted after initial startup and after 20 hours of operation. Impedance tests were performed at open circuit voltage and under varying loads in order to analyze the sources of resistance within the cell. A general increase in impedance was found after the 20h operation. Scanning electron micrographs of the cell microstructures found delamination and other defects which reduce performance. Suggestions for eradicating these issues and improving performance have been made.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Mechanical Systems
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Fagg, Duncan Paul. "Anodes for SOFCs (solid oxide fuel cells)." Thesis, University of Aberdeen, 1996. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU082955.
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The success of Solid Oxide Fuel Cells (S.O.F.C) rests heavily on material selection. The performances of several compounds were investigated as possible anode materials, starting with reduced titanates such as the magnesium titanate and zirconium titanate. These compositions, although possessing many qualities beneficial for use as an anode material, were found to be too unstable for practical use. For this reason further work concentrated on stable, zirconia based, compounds with exhibited mixed conduction under reducing atmospheres. The mobility of electronic carriers is considered to be much higher than that of ionic defects, therefore, promising mixed conductors can be formed by doping a good ionic conductor with a small concentration of transition metal ions. Zirconia based mixed conductors were studied for two reasons. Firstly, zirconia stabilised in the cubic defect fluorite structure, exhibits a high level of ionic conductivity. Secondly, it is the most common electrolyte material for an S.O.F.C. An anode based on zirconia would, therefore, be expected to offer a good physical compatibility with the electrolyte material and to exhibit a high ionic contribution to total conductivity. Large defect fluorite solid solutions in the systems Y2O3-ZrO2-Nb2O5, Yb2O3-ZrO2-Nb2O5 and CaO-ZrO2-Nb2O5 were established, which enabled the effects of composition, dopant size and charge on conduction to be investigated. These effects were shown to be linked to structure. From these results and comparisons with the Y2O3-ZrO2-TiO2 system, optimum, mixed conducting, compositions were established. The sample Y0.25Ti0.15Zr0.60O1.875 exhibited the best mixed conducting properties to date, obtained for compositions based on zirconia.
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Sarantaridis, Dimitrios. "Redox cycling of solid oxide fuel cells." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/11898.
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Lee, Won Yong Ph D. Massachusetts Institute of Technology. "Mathematical modeling of solid oxide fuel cells using hydrocarbon fuels." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74906.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references.
Solid oxide fuel cells (SOFCs) are high efficiency conversion devices that use hydrogen or light hydrocarbon (HC) fuels in stationary applications to produce quiet and clean power. While successful, HC-fueled SOFCs face several challenges, the most significant being performance degradation due to carbon deposition and the need of external reforming when using heavier HC. Modeling these devices faces these as well as other complexities such as the presence of multiple electrochemistry pathways including those of H2 and CO. The goals of this thesis are to: (1) improve the thermodynamic analysis of carbon deposition, (2) develop a multistep CO electrochemistry mechanism, and (3) apply the CO along with the H2 electrochemistry mechanisms to predict the cell performance when using syngas. Two carbon deposition mechanisms have been identified: homogeneously formed soot and catalytically grown carbon fiber. All previous thermodynamic analyses have used graphite to represent the properties of the deposited carbon regardless of the formation mechanism. However, the energetic and entropic properties of these two types of carbon are different from those of graphite. A new thermodynamic analysis is proposed that: (1) uses experimentally measured data for carbon fiber if the anode includes Ni catalyst; and (2) uses soot precursors such as CH3 and C2H2 to predict soot formation. The new approach improves the prediction of the onset of carbon deposition where previous analyses failed. A new multi-step CO electrochemistry model is proposed in which CO is directly involved in the charge-transfer steps. The model structure, with a single set of kinetic parameters at each temperature, succeeds in reproducing the characteristics of the EIS data of patterned anodes including the inductive loop at high activation overpotential. The model successfully predicts the steady-state Tafel plots, and explains the positive dependence of the exchange current density on Pco2 - Finally, a membrane-electrode-assembly (MEA) model is developed incorporating multispecies transport through the porous structure, detailed elementary heterogeneous reactions on the Ni surface, and for the first time, detailed electrochemistry models for H2 and CO. The model successfully reproduces the performance of SOFCs using pure H2 or CO. The MEA model can isolate/distinguish between the roles/contributions of the reforming chemistry and CO electrochemistry in SOFCs using syngas. Adding reforming thermochemistry improves the agreement with experiments at lower current densities, and raises the limiting current density by providing more H2 via the water-gas shift reaction. Adding CO electrochemistry improves the prediction at high current densities by the additional current generated by the CO electrochemical oxidation. The current from CO becomes comparable to that from H2 as the CO content at the TPB increases.
by Won Yong Lee.
Ph.D.
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Xu, Xiaoxiang. "Development of new proton conducting materials for intermediate temperature fuel cells /." St Andrews, 2010. http://hdl.handle.net/10023/887.
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Bedon, Andrea. "Advanced materials for Solid Oxide Fuel Cells innovation: reversible and single chamber Solid Oxide Fuel Cells, frontiers in sustainable energy." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3426788.
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The energy transition is changing the way we use, convert and store energy for all our purposes. It is a process driven by an increased acknowledgement of the relevant consequences of the current heavy use of fossil energy sources, and it is not clear where it will lead. Several technologies have been proposed as the best choice for the future of energy. Among them, Solid Oxide Fuel Cells (SOFCs) deserve a considerable attention. They are high temperature devices able to convert a variety of fuels (hydrogen, methanol, hydrocarbons, etc.) into electrical energy, with efficiencies that reach 90% when coupled with a heat recovery system. They can also be operated reversibly as Solid Oxide Electrolysis Cells (SOECs) and store electrical energy as fuels, so they can easily absorb the fluctuations of renewable energy production and save the energy until it is needed. Because of the high temperature of operation, they do not require noble metals. The SOFC technology is not mature yet for a large scale diffusion, but there is an intensive research towards this target. One of the main drawbacks of SOFCs is the short device life compared to the high costs, due to premature degradation of some cell components. This work of thesis is an attempt to increase economic convenience of SOFCs, by researching more stable materials and by decreasing the device costs. Particular attention has been devoted to find materials that are suitable for operation in reversible cells and Single Chamber cells (SC-SOFCs), two highly innovative variants of the basic SOFCs. A particular approach for the design of new materials has been proposed, consisting in coupling a Mixed Ionic Electronic Conductive (MIEC) substrate with an active phase, specifically chosen to obtain the properties desired for the respective application. The LSGF perovskite (La0.6Sr0.4Ga0.3Fe0.7O3) has been synthesized and fully characterized as the MIEC substrate. Then, it has been impregnated with cheap manganese and iron oxide, and the two different nanocomposites were studied in depth. Their activity as fuel cell electrodes has been tested, and very interesting performance of the iron composite as cathode and the manganese composite as anode has been recorded. A fuel cell based on LSGM electrolyte, with LSGF composite electrodes has been fabricated and successfully tested. The high homogeneity of this cell, that features very similar materials both as electrode and electrolyte, should prevent the formation of any insulating phase, and the nickel-free anode avoids problems related to nickel coarsening, so a higher durability of the device is guaranteed. LSGF has been tested as an electrode material for symmetric reversible cells, and promising results were obtained. A fully selective cathode material has been designed from Ca2FeAl0.95Mg0.05O5 brownmillerite, that has been impregnated with iron oxide. Decent performances were obtained, in spite of the relevant cheapness of the used elements. Preliminary results indicate that such a material could be used to operate SC-SOFCs without the extensive fuel losses that current state-of-the-art material cause.La transizione energetica sta cambiando il modo in cui usiamo, convertiamo e immagazziniamo l’energia per tutti i nostri scopi. Si tratta di un processo spinto dal crescente riconoscimento delle rilevanti conseguenze che l’attuale uso intensivo di fonti energetiche fossili comporta, e non è ancora chiaro esattamente a che situazione porterà. Sono molte le tecnologie che di volta in volta si trovano proposte come la soluzione principe per il futuro dell’energia. Tra di esse, le celle a combustibile a ossido solido (SOFC) meritano particolare attenzione. Sono dispositivi ad alta temperatura, in grado di convertire diverse tipologie di combustibili (idrogeno, metanolo, idrocarburi…) in energia elettrica, con efficienze che possono raggiungere il 90% se accoppiate con sistemi di recupero del calore. Queste celle a combustibile si possono operare anche reversibilmente come elettrolizzatori allo stato solido. Possono perciò immagazzinare energia elettrica come combustibile in modo da assorbire le fluttuazioni a cui è sottoposta la produzione di elettricità da fonti rinnovabili, fino al momento in cui c’è bisogno. Per via della alta temperatura operativa, non richiedono metalli nobili. La tecnologia delle SOFC non è ancora matura per una diffusione in larga scala, ma la ricerca in questo senso è intensa. Uno dei difetti principali di questi dispositivi è la ristretta vita operativa paragonata agli alti costi, a causa della degradazione prematura di alcuni componenti. Questo lavoro di tesi è un tentativo verso il miglioramento della sostenibilità economica delle SOFC, attraverso la ricerca di materiali più stabili e che permettano soluzioni più economiche. Particolare attenzione è stata riservata allo sviluppo di materiali adatti a operare in celle reversibili e a camera singola (SC-SOFC), due varianti innovative della SOFC di base. È stato proposto l’utilizzo di un approccio mirato per la progettazione dei nuovi materiali, consistente nell’accoppiamento di una fase conduttrice mista ionica ed elettronica (MIEC) che funge da substrato per una fase attiva, specificamente scelta per ottenere le proprietà ricercate per la rispettiva applicazione. La perovskite LSGF (La0.6Sr0.4Ga0.3Fe0.7O3) è stata sintetizzata e completamente caratterizzata come substrato a conduttività mista. Successivamente, è stata impregnata con ossidi di manganese e ferro, in virtù anche della loro economicità, e i due differenti nanocompositi così ottenuti sono stati studiati in dettaglio. La loro attività come elettrodi per celle a combustibile è stata testata, e si sono registrate prestazioni interessanti del nanocomposito con ferro come catodo e del nanocomposito con manganese come anodo. Una cella a combustibile basata su elettrolita LSGM e con elettrodi compositi a base LSGF è stata preparata e testata con successo. L’altissima omogeneità strutturale di questa cella, che sfrutta materiali molto simili sia come elettrolita che come elettrodi, sarebbe in grado di prevenire la formazione di qualsiasi fase isolante. Gli anodi privi di nichel evitano ogni problema legato all’accrescimento delle particelle di metallo, assicurando al dispositivo una migliore durabilità. LSGF è stato testato come materiale elettrodico per celle simmetriche reversibili, ottenendo risultati promettenti. Un materiale catodico interamente selettivo è stato sviluppato a partire dalla brownmillerite Ca2FeAl0.95Mg0.05O5, impregnata a sua volta con ossido di ferro. Con questo materiale si sono ottenute prestazioni discrete, nonostante l’economicità evidente degli elementi utilizzati. I risultati preliminari indicano che tali materiali potrebbero essere utilizzati per celle a camera singola evitando le ampie perdite di combustibile, inevitabili con l’uso dei catodi dell’attuale stato dell’arte.
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Yoon, Jongsik. "Nanostructured thin films for solid oxide fuel cells." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3164.
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Bulut, Basar. "Second Law Analysis Of Solid Oxide Fuel Cells." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1219161/index.pdf.
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In this thesis, fuel cell systems are analysed thermodynamically and electrochemically. Thermodynamic relations are applied in order to determine the change of first law and second law efficiencies of the cells, and using the electrochemical relations, the irreversibilities occuring inside the cell are investigated. Following this general analysis, two simple solid oxide fuel cell systems are examined. The first system consists of a solid oxide unit cell with external reformer. The second law efficiency calculations for the unit cell are carried out at 1273 K and 1073 K, 1 atm and 5 atm, and by assuming different conversion ratios for methane, hydrogen, and oxygen in order to investigate the effects of temperature, pressure and conversion ratios on the second law efficiency. The irreversibilities inside the cell are also calculated and graphed in order to examine their effects on the actual cell voltage and power density of the cell. Following the analysis of a solid oxide unit cell, a simple fuel cell system is modeled. Exergy balance is applied at every node and component of the system. First law and second law efficiencies, and exergy loss of the system are calculated.
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Wei, Xingguo. "Current distribution materials for solid oxide fuel cells." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/11527.
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Hart, Nigel T. "Functionally graded interfaces for solid oxide fuel cells :." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445940.
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Cooper, Richard John. "Flow and reaction in solid oxide fuel cells." Thesis, University of Birmingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367622.
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Payne, Clare Elizabeth Ann. "Novel fabrication techniques for solid oxide fuel cells." Thesis, Brunel University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318427.
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Shin, J. Felix. "New electrolyte materials for solid oxide fuel cells." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/7607/.
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Two general systems, brownmillerite-type Ba₂In₂O₅ and apatite-type silicates have been investigated for potential solid oxide fuel cell electrolyte applications. The combination of powder diffraction, NMR, TGA, Raman and AC impedance spectroscopy indicated the successful incorporation of phosphate, sulphate and silicate into the Ba₂In₂O₅ structure leading to a transition from an ordered brownmillerite-type structure to a disordered perovskite-type, which led to the conductivity enhancement below 800 °C, along with a significant protonic contribution in wet atmospheres. The CO₂ stability was also shown to be improved on doping. This oxyanion doping strategy has been extended to the analogous system, Ba₂Sc₂O₅, which resulted in samples with high conductivity and good stability towards CO₂. Neutron diffraction studies on La₉.₆Si₆O₂₆.₄ indicated that the interstitial oxide ion is located near the channel centre. Further interstitial anions could be accommodated through hydration, which led to displacement of the interstitial site away from the channel centre, with an accompanying swelling of the channel. Although long term annealing of these apatite silicates showed no apparent significant structural change, a reduction in the bulk conductivity was observed, while the grain boundary conductivity was improved, thus resulting in a small enhancement in the total conductivity below 400 °C.
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Almutairi, Ghzzai. "Ageing of integrated-planar solid Oxide Fuel Cells." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4422/.
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The ageing of Solid Oxide Fuel Cells (SOFCs) is a key problem because of the requirement of 50,000 hours to their lifetime in many applications. At present, such performance is still not attainable because degradation occurs at more than 1% per thousand hours under practical test conditions. In this thesis, the ageing of the Rolls Royce Fuel Cell Systems (RRFCS)Integrated Planar Solid Oxide Fuel Cell (IP-SOFC) was studied under different operating conditions, especially by accelerated degradation testing (ADT), in order to investigate the fuel cell stability and degradation behaviour under non-steady operating conditions for further improvement of the systems. This work demonstrates that the long-term durability of the IP-SOFC is very good when pure hydrogen is used as fuel. However, the introducing of even a small amount of methane in fuel has demonstrated the capacity to damage the IP-SOFC through the formation of carbon deposits on the anode surface. Future work is therefore required to identify viable alternative materials and optimal operating conditions.
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Sandells, Jamie Ian. "Mathematical modelling of planar solid oxide fuel cells." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4908/.
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In this thesis we construct a series of mathematical models from first principles to examine the advection, diffusion and reactions of species within a planar Solid Oxide Fuel Cell (SOFC). We reduce the complexity of an SOFC to flow and reaction across a flat, impermeable plate and begin by establishing a simplistic model for the incompressible, isothermal flow and reaction of hydrogen. Throughout the thesis we seek to extend this initial model by adding appropriate levels of complexity such as alternative fuels, compressibility and thermal effects. In establishing solutions to these models we use a series of analytical techniques. We adopt the concept of boundary-layer flow and self similarity to simplify the model equations into a form where we can obtain analytical and efficient numerical solutions. We also utilise asymptotics to examine and validate the model around regions of singularities within the flow. Within each model we have examined the electrical performance of the cell and in some cases we have validated these results with existing experimental data.
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Guzman, Montanez Felipe. "SAMARIUM-BASED INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS." University of Akron / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=akron1134056820.
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Parihar, Shailendra S. "High Temperature Seals for Solid Oxide Fuel Cells." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1172490697.
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Kobayashi, Teruaki. "Development of materials for solid oxide fuel cells." Kyoto University, 2008. http://hdl.handle.net/2433/135588.
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Kyoto University (京都大学)0048
新制・課程博士
博士(エネルギー科学)
甲第13953号
エネ博第174号
新制||エネ||40(附属図書館)
UT51-2008-C869
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)教授 八尾 健, 教授 萩原 理加, 准教授 日比野 光宏
学位規則第4条第1項該当
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De, la Torre Garcia Ricardo. "Production of Micro-Tubular Solid Oxide Fuel Cells." Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/368790.
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An innovative current collection architecture for micro-tubular solid oxide fuel cells (SOFC) has been developed. A nickel wire is coiled around a thin carbon composite rod in order to fabricate cell supports. Different carbon composites such as pencil leads and carbon fibres were investigated. The cell support was then coated with ceramic slurries based NiO/YSZ and YSZ for anode and electrolyte, respectively, by successive dip coatings. Effect of thermal behaviour, porosity, amount of binder and dip coating parameters were conjunctly analysed to produce anode and electrolyte crack-free layers with the thickness desired. Pyrolisable materials were then eliminated under air atmosphere at 800ºC followed by co-sintering of half-cells at 1380ºC for 2 h in argon to avoid the oxidation of the nickel wire. In order to complete the cells, sintered half-cells were dipped into cathode inks consisted of LSM-YSZ composite for a functional layer and LSM pure to increase the electrical conductivity of the cathode. The cathode was also sintered at 1150ºC for 2 h under argon atmosphere.
Complete cells with an outer diameter below 1.2 mm and length of 30 mm with an effective cathode length of 20 mm and whose active cathode area is 0.75 cm2 were produced.
The efficiency of the current collector method developed is evaluated by comparison with the performance of a micro-tubular cell produced and tested under similar conditions, but with a common current collection method. The results of I-V curves shown that the innovative current collection method enhances the performance of a typical micro-tubular cell in the order of 3-4 times. The improvement in performance is attributed to the reduction of current paths of the micro-tubular cells.
Suggestions for the production and characterization of current collector-supported micro-tubular cells are also given.
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De, la Torre García Ricardo. "Production of Micro-Tubular Solid Oxide Fuel Cells." Doctoral thesis, University of Trento, 2011. http://eprints-phd.biblio.unitn.it/541/1/PRODUCTION_OF_MICRO-TUBULAR_SOLID_OXIDE_FUEL_CELLS.pdf.
Full textAbstract:
An innovative current collection architecture for micro-tubular solid oxide fuel cells (SOFC) has been developed. A nickel wire is coiled around a thin carbon composite rod in order to fabricate cell supports. Different carbon composites such as pencil leads and carbon fibres were investigated. The cell support was then coated with ceramic slurries based NiO/YSZ and YSZ for anode and electrolyte, respectively, by successive dip coatings. Effect of thermal behaviour, porosity, amount of binder and dip coating parameters were conjunctly analysed to produce anode and electrolyte crack-free layers with the thickness desired. Pyrolisable materials were then eliminated under air atmosphere at 800ºC followed by co-sintering of half-cells at 1380ºC for 2 h in argon to avoid the oxidation of the nickel wire. In order to complete the cells, sintered half-cells were dipped into cathode inks consisted of LSM-YSZ composite for a functional layer and LSM pure to increase the electrical conductivity of the cathode. The cathode was also sintered at 1150ºC for 2 h under argon atmosphere.
Complete cells with an outer diameter below 1.2 mm and length of 30 mm with an effective cathode length of 20 mm and whose active cathode area is 0.75 cm2 were produced.
The efficiency of the current collector method developed is evaluated by comparison with the performance of a micro-tubular cell produced and tested under similar conditions, but with a common current collection method. The results of I-V curves shown that the innovative current collection method enhances the performance of a typical micro-tubular cell in the order of 3-4 times. The improvement in performance is attributed to the reduction of current paths of the micro-tubular cells.
Suggestions for the production and characterization of current collector-supported micro-tubular cells are also given.
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CONTI, BRUNO. "Solid Oxide Fuel Cells: Numerical and Experimental Approaches." Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/943177.
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Solid oxide fuel cell (SOFC) is a promising electrochemical technology that can produce electrical and thermal power with outstanding efficiencies. A systematic synergetic approach between experimental measurements and modelling theory has proved to be instrumental to evaluate performance and correct behaviour of a chemical process, like the ones occurring in SOFC. For this purpose, starting from SIMFC (SIMulation of Fuel Cells) code set-up by PERT-UNIGE (Process Engineering Research Group) for Molten Carbonate Fuel Cells [1], a new code has been set-up for SOFCs based on local mass, energy, charge and momentum balances. This code takes into account the proper reactions occurring in the SOFC as well as new geometries and kinetics thanks to experiments carried out on single cells and stack in ENEA laboratories of C.R. Casaccia and VTT Fuel Cell Lab in Finland. In particular using an innovative experimental setup it has been possible to study experimentally the influence of a multicomponent mixtures on the performance of SOFC and also validate locally a 2-D model developed starting from SIMFC code. The results obtained are good, showing a good agreement between experimental and numerical results. The obtained results are encouraging further studies which allow the model validation on a greater quantity of data and under a wider range of operating conditions.
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Zalar, Frank M. "Model and theoretical simulation of solid oxide fuel cells." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1189691948.
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Ford, James Christopher. "Thermodynamic optimization of a planar solid oxide fuel cell." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45843.
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Solid oxide fuel cells (SOFCs) are high temperature (600C-1000C) composite metallic/ceramic-cermet electrochemical devices. There is a need to effectively manage the heat transfer through the cell to mitigate material failure induced by thermal stresses while yet preserving performance. The present dissertation offers a novel thermodynamic optimization approach that utilizes dimensionless geometric parameters to design a SOFC. Through entropy generation minimization, the architecture of a planar SOFC has been redesigned to optimally balance thermal gradients and cell performance. Cell performance has been defined using the 2nd law metric of exergetic efficiency. One constrained optimization problem was solved. The optimization sought to maximize exergetic efficiency through minimizing total entropy production while constraining thermal gradients. Optimal designs were produced that had exergetic efficiency exceeding 92% while maximum thermal gradients were between 219 C/m and 1249 C/m. As the architecture was modified, the magnitude of sources of entropy generation changed. Ultimately, it was shown that the architecture of a SOFC can be modified through thermodynamic optimization to maximize performance while limiting thermal gradients. The present dissertation highlights a new design methodology and provides insights on the connection between thermal gradients, performance, sources of entropy generation, and cell architecture.
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Coles-Aldridge, Alice. "Substituted ceria materials for applications in solid oxide fuel cells." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/14622.
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Cerias, appropriately doped with trivalent rare earth ions in particular, can have high oxide ion conductivity and are attractive as both SOFC (solid oxide fuel cell) electrolytes and anodes. Here, four groups of candidate electrolyte materials were synthesised using a low temperature method in order to determine the effect of multiple doping on their microstructure and ionic conductivity. In an initial study, seven compositions of Ce0.8SmxGd[sub]yNd[sub]zO1.9 (where x, y and z = 0.2, 0.1, 0.0667 or 0 and x + y + z = 0.2) were synthesised and the properties of multiply-doped materials were compared with the corresponding singly-doped parent materials. The effect of co-doping with Gd and Sm was investigated in more detail by preparing and studying five compositions of Ce1−2xSmxGdxO2−x (where x = 0.125, 0.1, 0.0875, 0.075 or 0.05) and seven compositions of Ce0.825SmxGd0.175−xO1.9125 (where x = 0.175, 0.14, 0.105, 0.0875, 0.07, 0.035 or 0). The effect of additional doping with a divalent ion- Ca2+- was studied in six compositions of Ce[sub](0.825+y)Sm[sub](0.0875-y)Gd[sub](0.0875-y)Ca[sub]yO1.9125 (where y = 0, 0.00875, 0.0175, 0.02625, 0.035 or 0.04375). The materials were characterised using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry and X-ray diffraction. Crystallite sizes were determined in the powders and relative densities and grain size distributions were obtained in sintered pellets. Total, bulk and grain boundary conductivities were obtained using impedance spectroscopy and corresponding activation energies and enthalpies of ion migration and defect association were calculated. The most promising material for SOFCs operating at intermediate temperatures was found to be Ce0.825Sm0.0875Gd0.0875O1.9125 which had a total conductivity at 600 °C of 2.23 S m−1. Lastly, doped ceria materials, primarily Ce0.8Sm0.2O1.9, were employed as catalytic supports for Pd and PdO nanoparticles and these were investigated as SOFC anode materials.
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SANTANA, LEONARDO de P. "Estudo de conformacao de ceramicas a base de zirconia para aplicacao em celulas a combustivel do tipo oxido solido." reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11727.
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Made available in DSpace on 2014-10-09T12:55:11Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:06:02Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Compson, Charles E. "Design, Fabrication and Characterization of Novel Planar Solid Oxide Fuel Cells." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14477.
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Planar solid oxide fuel cells (SOFCs) were designed, fabricated and characterized in order to develop a (1) cost-effective method for fabrication of thin electrolyte layers, (2) hermetic sealing and (3) stable interconnects. Electrophoretic deposition (EPD) was discovered to be an excellent method for fabricating dense electrolyte layers of about 5m thick on porous non-conducting substrates. The EPD process was thoroughly studied from proof-of-concept to statistical reproducibility, deposition mechanism, modeling and process optimization. Deposition on non-conducting substrates was found to follow many of the same fundamental trends as that on conductive substrates except for the voltage efficiency and detailed charge transfer mechanism. Eventually, the process was optimized such that an SOFC was fabricated that achieved 1.1W/cm2 at 850C. Further, a novel sealless planar SOFC was designed that incorporates a hermetic interface between the electrolyte and interconnect similar to tubular and honeycomb designs. The hermetic interface successfully acted as a blocking electrode under DC polarization, indicating its potential to act as a sealant. Leakage rates across the interface were 0.027sccm at 750c, similar to polycrystalline mica seals. Through a process of tape casting and lamination, a two-cell stack without sealant was fabricated and achieved a power density of 75mW/cm2 at 750C. Finally, the degradation rate of silver and silver-based interconnects was studied under static and dual-atmosphere conditions. Corrosion of silver grain boundaries along with sublimation losses results in the formation of large pores, resulting in up to 30 of anode oxidation after 8hrs testing at 750c. Further stability studies indicated that silver-based interconnects would be better suited for applications at operating temperatures less than 650C.
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Ghosh, Ujjal. "One dimensional modeling of planar solid oxide fuel cell." Ohio : Ohio University, 2005. http://www.ohiolink.edu/etd/view.cgi?ohiou1177438858.
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Aruppukottai, Muruga Bhupathi Saranya. "Integrating nanoionics concepts in micro solid oxide fuel cells." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/362363.
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Fuel cells are one of the promising technology at present to meet the growing demand of clean energy and technology. Among the different varieties of fuel cells, Solid Oxide Fuel Cell (SOFC) research is advancing towards the device miniaturization (called “micro-SOFC” with thin film components) with the operation temperature in the range ≈ 500°C to 700°C for portable device application.
In SOFC components, cathode causes major polarization loss due to the sluggishness of oxygen reduction reaction (ORR) at low operating temperature that would affect the device efficiency. To rectify this there are various groups working towards the enhancement of cathode functionality at low operating temperature. Generally, the functionality of cathode can be enhanced by two ways i) improving the intrinsic properties of existing cathode materials by making modifications in the cathode microstructure ii) search for the new cathode materials.
The thin film cathodes studied in this thesis are La0.8Sr0.2MnO3+δ (LSM), La0.8Sr0.2CoO3-δ (LSC) and La0.8Sr0.2Mn1-xCoxO3±δ (LSMC; from x=0 to 1) a pseudo-binary system, which are Mixed Ionic Electronic Conductors (MIEC) conduct both ions and electrons. The aforementioned two ways are followed in this thesis to enhance the cathode functionality by implementing nanoionics concept.
The behavior of ionic conduction in nano-regime (<100nm) is totally different than bulk and the study of such ionic transport in nanoscale is the field of nanoionics. Especially, the interfaces such as space-charge layer and grain boundaries act as a highway for fast oxygen ion conduction that can enhance the overall charge transport in the nanostructures. In this thesis, oxygen mass transport properties are studied in cathodes in thin film form by making modifications in the thin film nanostructure in order to observe and enhance the charge transport along the interface of grain boundaries as well as to understand the fast ionic transport in such interfaces.
Generally, the thin film nanostructure offered by Pulsed Laser Deposition (PLD) exhibit columnar grains that can act as a highway for ionic conduction and suitable for the proposed work. Therefore PLD is used as a tool to study the ionic transport in the interfaces. Further, LSM/LSC multilayer deposition studies are conducted in PLD to find out the optimum thickness for the fabrication of a combinatorial LSMC pseudo-binary system without any parasitic phases.
Among the cathode materials studied in this thesis, LSM is a classical and well-studied cathode material. The functional properties i.e. oxygen mass transport properties (oxygen self-diffusion and surface exchange coefficients, D^*and k^*, respectively) of LSM thin film cathodes are studied by Isotope Exchange depth Profiling using Secondary ion Mass Spectroscopy (IEDP-SIMS) and Electrochemical Impedance Spectroscopy (EIS) techniques in the temperature range 500°C to 700°C.
In the study on LSMC pseudo-binary, a novel (new) methodology is presented for the screening of materials for SOFC application. The methodology is based on a combinatorial deposition of thin films by PLD on 4-inch silicon wafers, further it is possible to predict the thickness and compositional map of LSMC binary using this methodology. The proposed methodology can be extended for generating full range binary and ternary diagrams of compositions even for very complex oxides (due to an excellent transfer of the stoichiometry). IEDP-SIMS is carried out for evaluating oxygen mass transport properties of LSMC system in the compositions with cobalt content x ≈ 0.04 to 0.85 in the temperature range 600°C to 800°C.
This thesis is divided into six chapters and a short summary to each chapter is given below including appendix.
Chapter 1: An introduction to the scope of the thesis.
Chapter 2: An introduction to the experimental method employed in this thesis.
Chapter 3: Parent materials (LSM and LSC) microstructural optimization in PLD.
Chapter 4: Oxygen ion transport study in LSM thin film cathodes.
Chapter 5: Fabrication and microstructural characterization of LSMC thin film pseudo-binary system.
Chapter 6: Oxygen ion transport study in LSMC thin film system.
Appendix A: Introduction to Two-slab model.
Appendix B: Fabrication of LSM-LSC-LSF pseudo-ternary system.La Nanoiónica se ha convertido en un campo cada vez más prometedor para el futuro desarrollo de dispositivos avanzados de conversión y almacenamiento de energía, tales como baterías, pilas de combustible y supercondensadores. En particular, los materiales nanoestructurados ofrecen propiedades únicas o combinaciones de propiedades en electrodos y electrolitos en una gama de dispositivos de energía. Sin embargo, la mejora de las propiedades de transporte de masa a nivel nano, a menudo se ha encontrado que son difíciles de implementar en nonoestructuras. En esta tesis, se investigó el transporte de iones oxígeno en cátodos tipo perovskita-conductor mixto iónico y electrónico (MIEC) de capa delgada (grosor < 200nm) con una estructura nonoestructurada, con el objetivo de correlacionar el transporte de iones oxígeno con la estructura del film a nivel de grano interior y límite de grano. El trabajo desarrollado en esta tesis se ha dividido en seis partes. El primer capítulo, introduce los conceptos básicos de las pilas de combustible de óxido sólido, la importancia de los cátodos de película delgada y el concepto de nanoiónica. El segundo capítulo explica el principio y el funcionamiento de todas las técnicas experimentales empleadas en esta tesis para la caracterización microestructural y funcional de los cátodos de película delgada. Los siguientes capítulos contienen el trabajo principal de la tesis. Las condiciones de deposición y estudios de optimización microestructural realizados mediante PLD para fabricar cátodos de película delgada se compilan en el capítulo tres. Las propiedades de transporte de iones de oxígeno del La0.8Sr0.2MnO3+δ (LSM) de películas delgadas se estudian en el capítulo cuatro. Además, en el capítulo cinco se presenta una nueva metodología de proyección de materiales, para celdas de combustible de óxido sólido (SOFC). La metodología se basa en una deposición combinatoria de La0.8Sr0.2Mn1-xCoxO3±δ (LSMC) por PLD en una oblea de silicio de 4 pulgadas que permite la generación de un diagrama binario completo de composiciones, incluso para óxidos complejos. El capítulo seis se dedica a los estudios funcionales del sistema binario LSMC La técnica de intercambio de isotopos en perfiles profundos combinada con la espectroscopia iónica de masas (IEDP-SIMS) se empleó en el rango de temperatura de 500°C a 800°C para la evaluación de las propiedades de transporte de masa de oxígeno del LSM y el sistema binario LSMC. Además, las propiedades de transporte de masa de oxígeno del LSM se estudió mediante Espectroscopia de Impedancia Electroquímica (EIS).
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Arespacochaga, Santiago Nicolás de. "Sewage biogas energy valorization via solid oxide fuel cells." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/345237.
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A more sustainable and secure energy supply is required for the forthcoming generations; where the actual dependence on the fossil fuel reserves should be replaced by self-sufficiency and use of renewable energy resources. Conventional sewage treatment is an energy consuming process, or more specifically, an electricity consuming process. Notwithstanding, energy on Waste Water Treatment Plants is not only considered in terms of consumption reduction, but also in terms of production of renewable energy in form of biogas. Today, achieving energy self-sufficiency is limited by the low electrical efficiencies of conventional biogas-powered Combined Heat and Power systems; but fuel cell technology is appearing on the scene in the recent years offering both a higher electrical efficiency and a further reduced environmental impact. Biogas energy valorization in fuel cells combines a high-efficient technology for electrical generation, i.e.: fuel cell, with the use of a renewable fuel, i.e.: biogas.
Raw biogas contains a wide range of contaminants, mainly sulfur and organic silicon compounds (siloxanes), which pose a risk to Solid Oxide Fuel Cell operation; hence biogas requires a thorough conditioning and cleaning process upstream the fuel cell unit. Moreover, monitoring of siloxanes levels remained somewhat controversial with discrepancies on optimal sampling procedure as well as quantification technique; hindering the design and operation of siloxanes removal technologies.
This work is devoted to studying and validating the whole biogas energy valorization line, including the biogas treatment system and the fuel cell operation. The integration of low-cost biological desulphurization and deep polishing physico-chemical adsorption processes with a Solid Oxide Fuel Cell has been studied in an industrial 2.8 kWe pilot plant installed in a Waste Water Treatment Plant in Spain, showing that the stringent gas quality requirements of 0.5 ppmv S and 1 mg Si/Nm3 can be satisfied with over the long-term. The technical and economic comparison of Solid Oxide and Molten Carbonate Fuel Cell performance with conventional Internal Combustion Engines and Micro-Turbines has been also conducted for different plant sizes and raw biogas compositions, confirming the relevant role that fuel cells can play on carbon neutral sewage treatment; particularly in small- and medium-size plants.
Today the final justification for biogas valorization in fuel cell systems needs to be found in environmental issues as some improvements both in the performance and costs are still required. Nonetheless, this thesis demonstrates that the economics for this next-generation technology are expected for the short-term. Further collaborative research between biogas producers, suppliers of biogas treatment systems and manufacturers of fuel cells is required in the near future for Solid Oxide Fuel Cell technology deployment in the sewage sector.El subministrament d'energia sostenible i segur és un dels reptes més rellevants per a les properes generacions, on la dependència actual en les fonts d'energia basades en combustibles fòssils haurà de ser substituïda per l'autosuficiència i l'ús dels recursos energètics renovables. El tractament convencional d'aigües residuals urbanes és un procés que consumeix grans quantitats d'energia, o més específicament, grans quantitats d'electricitat. En aquest sentit, l'energia a les Estacions Depuradores d'Aigües Residuals s'ha de tractar no només en termes de reducció del consum, sinó també en termes de producció d'energia renovable a partir del biogàs. Avui en dia, no és possible assolir l'autosuficiència energètica a causa de les baixes eficiències elèctriques dels sistemes de cogeneració convencionals alimentats per biogàs. Tot i això, en els darrers anys, la tecnologia de les piles de combustible està apareixent en escena, oferint una millor eficiència elèctrica i una reducció en l'impacte ambiental. La valorització energètica de biogàs en piles de combustible combina una tecnologia d'elevada eficiència per a la generació d'energia (la pila de combustible), amb l'ús d'un combustible renovable (el biogàs). S'ha de tenir en compte que el biogàs brut conté una àmplia gamma de contaminants, especialment compostos de sofre i de silici orgànic (siloxans), que comporten un risc operatiu per al correcte funcionament de les piles de combustible d'òxid sòlid. Per tant, s'ha d'instal·lar una etapa d'acondicionament i neteja exhaustiu del biogàs abans que es pugui introduïr a la pila de combustible. D'altra banda, la monitorització de les concentracions de siloxans presenta discrepàncies en relació al procediment òptim per al seu mostreig i en la tècnica analítica de quantificació; dificultant d'aquesta manera el disseny i la operació de les tecnologies d'eliminació d'aquests compostos. Aquest treball es centra en l'estudi i validació de tota la línia de valorització energètica, incloent el sistema de tractament de biogàs i la operació de la pila de combustible. S'ha estudiat la integració de tecnologies de dessulfuració biològica de baix cost i de processos d'adsorció fisicoquímica amb una pila de combustible d'òxid sòlid en una planta pilot industrial de 2.8 kWe instal·lada en una Estació Depuradora d'Aigües Residuals a Catalunya (Mataró). Els resultats experimentals han demostrat que les tecnologies de tractament de biogàs són capaces d'assolir els exigents nivells de qualitat de 0.5 ppmv S i 1 mg Si/Nm3 tant en el curt com en el llarg plaç. Per altra part, s'ha realitzat una estudi tècnic-econòmic comparatiu entre les piles de combustible (d'òxid sòlid i de carbonat fos) amb els motors de combustió interna i les microturbines per a diferents tamanys de planta i composicions del biogàs. D'aquesta manera, s'ha confirmat el paper important que poden jugar les piles de combustible en l'assoliment d'un tractament d'aigües residuals autosuficient; particularment en plantes de tamany petit i mitjà. Avui en dia, els projectes de valorització energètica de biogàs a través de piles de combustible encara s'han de justificar per raons ambientals ja que es requereixen millores tant en el rendiment tècnic com en els costos d'inversió. No obstant, aquesta tesi demostra que aquesta tecnologia de pròxima generació serà econòmicament viable en el curt termini i podrà competir amb les tecnologies convencionals. La investigació col·laborativa entre productors de biogàs, proveïdors de tecnologies de tractament i fabricants de piles de combustible serà imprescindible durant els propers anys per tal que la tecnologia pugui convertir-se en una realitat en el sector del tractament d'aigües residuals urbanes.
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Willich, Caroline [Verfasser]. "Local Characterisation of Solid Oxide Fuel Cells / Caroline Willich." Aachen : Shaker, 2013. http://d-nb.info/1051574064/34.
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Sivasundram, Gopiraj. "Composite cathodes for intermediate temperature solid oxide fuel cells." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/11518.
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Beckel, Daniel. "Thin film cathodes for micro solid oxide fuel cells." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:29741.
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Baron, Sylvia A. "Anodes for solid oxide fuel cells with ceria electrolytes." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410219.
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Kerman, Kian. "Ultra-thin solid oxide fuel cells: materials and devices." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11418.
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Solid oxide fuel cells are electrochemical energy conversion devices utilizing solid electrolytes transporting O2- that typically operate in the 800 - 1000 °C temperature range due to the large activation barrier for ionic transport. Reducing electrolyte thickness or increasing ionic conductivity can enable lower temperature operation for both stationary and portable applications. This thesis is focused on the fabrication of free standing ultrathin (<100 nm) oxide membranes of prototypical O2- conducting electrolytes, namely Y2O3-doped ZrO2 and Gd2O3-doped CeO2. Fabrication of such membranes requires an understanding of thin plate mechanics coupled with controllable thin film deposition processes. Integration of free standing membranes into proof-of-concept fuel cell devices necessitates ideal electrode assemblies as well as creative processing schemes to experimentally test devices in a high temperature dual environment chamber. We present a simple elastic model to determine stable buckling configurations for free standing oxide membranes. This guides the experimental methodology for Y2O3-doped ZrO2 film processing, which enables tunable internal stress in the films. Using these criteria, we fabricate robust Y2O3-doped ZrO2 membranes on Si and composite polymeric substrates by semiconductor and micro-machining processes, respectively. Fuel cell devices integrating these membranes with metallic electrodes are demonstrated to operate in the 300 - 500 °C range, exhibiting record performance at such temperatures. A model combining physical transport of electronic carriers in an insulating film and electrochemical aspects of transport is developed to determine the limits of performance enhancement expected via electrolyte thickness reduction. Free standing oxide heterostructures, i.e. electrolyte membrane and oxide electrodes, are demonstrated. Lastly, using Y2O3-doped ZrO2 and Gd2O3-doped CeO2, novel electrolyte fabrication schemes are explored to develop oxide alloys and nanoscale compositionally graded membranes that are thermomechanically robust and provide added interfacial functionality. The work in this thesis advances experimental state-of-the-art with respect to solid oxide fuel cell operation temperature, provides fundamental boundaries expected for ultrathin electrolytes, develops the ability to integrate highly dissimilar material (such as oxide-polymer) heterostructures, and introduces nanoscale compositionally graded electrolyte membranes that can lead to monolithic materials having multiple functionalities.Engineering and Applied Sciences
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Akhtar, Naveed. "Single-chamber solid oxide fuel cells : modelling and experiments." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/626/.
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The objective of this work is to compare the performance of different geometries (i.e. planar, coplanar and micro tubular) under single-chamber (mixed-reactant) solid oxide fuel cell (SC-SOFC) conditions. In this respect, these designs have been computer analyzed and it is found that the micro-tubular design eliminates the possibility of cross diffusion/convection from the counter electrode, which is an inherent disadvantage in planar and co-planar designs. This is the first experimental report describing that the micro-tubular design offers the highest fuel utilization, cell efficiency and an acceptable level of performance (under single-chamber conditions) as compared to other designs. With the help of developed numerical model (also the first one, on mixed-reactant, micro-tubular design), it is demonstrated that there is a possibility of further improvement in performance, e.g. cell positioning, micro-tube diameter and cathode morphology (its micro-structure and material) are important factors to consider. Other parameters such as, flow rate, temperature and mixing ratio are also very effective in improving the cell performance but these parameters should be carefully controlled in order to avoid their counter-effects, like, lower fuel utilization, material degradation, anode coking and oxidation-reduction. There are some other parameters such as, electrode porosity, permeability and cathode radiative emissivity, which have minimal effect in performance enhancement and it is suggested before investing time on these parameters, a net energy and cost analysis would be very helpful. There are still some issues with choosing appropriate materials for building an SC-SOFC with both an acceptable lifetime and production of electrical energy. While it has been observed that most of the problems related to material degradation are thermally driven, it would be very helpful to lower the operating temperature by using intermediate temperature SOFC materials. Further to this, long term degradation studies and performance cycling will benefit in order to determine their suitability under mixed-reactant environment.
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Dikwal, Chinnan Maclean. "Cycling studies of micro-tubular solid oxide fuel cells." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/299/.
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A major problem of solid oxide fuel cells (SOFCs) is their long term durability under cyclic operation, for example during start-up and shutdown, where cracking can occur. The objective of this project is to understand these mechanisms of cyclic degradation for micro-tubular SOFC, then to set-up experiments to measure the degradation in terms of the drop in electrochemical performance and subsequently confirming the theories by dilatometry and scanning electron microscopy (SEM). In conclusion, the methods and conditions for minimizing degradation in SOFC have been put forward. First, a theory of degradation based micro-crack propagation due to severe expansion and direct oxidation of the Ni anode were propounded. Several experiments were designed to illustrate the degradation phenomena. The first was isothermal (steady state) ageing, which was performed to provide a benchmark of degradation for easy comparison with degradation under transient conditions (i.e. thermal, redox and load cycling). During this operation, sintering was found to dominate the degradation mechanism, causing irreversible deformation and decreasing the power output without obvious micro-cracking taking place. With the bench mark for steady state degradation established, thermal cycling was performed by rapidly alternating between peak temperature and 200⁰C. This was found to have a marginal effect on the electrochemical performance and no microcracking was observed. However, thermal cycling with a temperature gradient imposed across the tubes was found to cause electro-chemical performance decrease and micro-cracking and de-laminations were observed. Thirdly, redox cycling was performed by changing the fuel flow between 20mL/min and no-flow. This was essential to deprive the anode of fuel in order to allow for oxidation of the Ni anode to occur. Redox cycling was found to have an adverse effect on the electro-chemical performance of micro-tubes. Severe micro-cracking and delaminations were observed. Lastly, thermal and electrical shock test were performed. The critical fracture temperature (ΔTC) was established by thermal shock at approximately 180⁰C. Under electrical shock testing, the tubes were found to fail after 13 – 15 electrical shock cycles, depending on the shock temperature. In conclusion, theories of micro-tubular SOFC cycling degradation have been proposed for thermal cycling, redox cycling and isothermal ageing and several experiments have provided confirmation.
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Jorgensen, Mette Juhl. "Lanthanum manganate based cathodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343243.
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Wright, Eileen. "End-of-life management of solid oxide fuel cells." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/9103.
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This thesis reports on research undertaken to investigate the end-of-life management of solid oxide fuel cells (SOFC), through the definition of a framework and the development of a multicriteria evaluation methodology which together support comparison of alternative end-of-life scenarios. The primary objective of this research is to develop an understanding of the challenges and opportunities arising during the end-of-life phase of the technology, such that any conflicts with end-of-life requirements might be addressed and opportunities for optimising the end-of-life phase fully exploited. The research contributions can be considered in four principal parts. The first part comprises a review of SOFC technology and its place in future sustainable energy scenarios, alongside a review of a growing body of legislation which embodies concepts such as Extended Producer Responsibility and Integrated Product Policy. When considered in the context of the life cycle assessment literature, which clearly points to a lack of knowledge regarding the end-of-life phase of the SOFC life cycle, this review concludes that the requirement for effective end-of life management of SOFC products is an essential consideration prior to the widespread adoption of commercial products. The second part of the research defines a framework for end-of-life management of SOFCs, which supports clarification of the challenges presented by the SOFC stack waste stream, as well as identifying a systematic approach for addressing these challenges through the development of alternative end-of-life management scenarios. The framework identifies a need to evaluate the effectiveness of these end-of-life scenarios according to three performance criteria: legislative compliance; environmental impact; and economic impact. The third part of the research is concerned with the development of a multi-criteria evaluation methodology, which combines conventional evaluation methods such as life cycle assessment and cost-benefit analysis, with a novel risk assessment tool for evaluating compliance with current and future legislation. A decision support tool builds on existing multi-criteria decision making methods to provide a comparative performance indicator for identification of an end of-life scenario demonstrating low risk of non-compliance with future legislation; low environmental impact; and a low cost-benefit ratio. Finally, the validity of the framework for end-of-life management is tested through the completion of two case studies. These case studies demonstrate the flexibility of the framework in supporting a reactive end-of-life management approach, whereby end-of-life management is constrained by characteristics of the product design, and a proactive approach, whereby the impact of design modification on the end-of-life phase is explored. In summary, the research clearly highlights the significance of the end-of-life stage of the SOFC life cycle. On the one hand, failure to manage end-of-life products effectively risks undermining the environmental credentials of the technology and is likely to lead to the loss of a high-value, resource-rich material stream. On the other hand, the early consideration of aspects identified in the research, especially while opportunities remain to influence final product design, represents a real opportunity for optimising the end-of-life management of SOFC products in such a way as to fully realise their potential as a clean and efficient power generation solution for the future.
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Hedayat, Nader. "Fabrication of Planar and Tubular Solid Oxide Fuel Cells." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1427973683.
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