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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.
Texte intégralRésumé :
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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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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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.
Texte intégralRésumé :
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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Choi, Hyunkyu. « Perovskite-type oxide material as electro-catalysts for solid oxide fuel cells ». The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1354652812.
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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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Johnson, Janine B. « Fracture Failure of Solid Oxide Fuel Cells ». Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4847.
Texte intégralRésumé :
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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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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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.
Texte intégralRésumé :
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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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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Ford, James Christopher. « Thermodynamic optimization of a planar solid oxide fuel cell ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45843.
Texte intégralRésumé :
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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An, Ke. « Mechanical Properties and Electrochemical Durability of Solid Oxide Fuel Cells ». Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11088.
Texte intégralRésumé :
The mechanical properties of unaged and aged constituent materials for solid oxide fuel cells were evaluated using microindentation, plate tensile, four-point bend, ball on ring and pressure on ring tests. The Vickers hardness of the anode, interconnect and electrolyte was determined before and after 1000 hours aging at 1000 oC in air. The fracture toughness KIC was found for the electrolyte materials. Finite element analysis (FEA) was validated and used to calculate the stress distribution and peak stress for the biaxial strength test. A Weibull analysis was carried out on the test/FEA-predicted peak stresses, and Weibull strength, modulus and material scale parameters were found for each test methodology. The methodologies were evaluated based on the results of the Weibull analysis and the pressure on ring test is preferred one for brittle thin film fracture strength testing.
Half cell SOFCs with composite cathode (Pr0.7Sr0.3)MnO3±δ /8YSZ on the 8YSZ electrolyte were aged 1000 hours at 1000 oC in air with/without polarization and investigated using Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (B.E.T.) method and X-ray Diffraction (XRD). The performance of the half cell SOFCs degraded after aging with/without polarization compared to the initial state, which was ascribed to the decrease of the electrolyte conductivity. The current load was shown to have impact on the performance by slowing down the decreasing rate of the polarization resistance of the SOFCs. After aging, the microstructural properties - pore size and pore volume changed, and growth of grains was found on the (Pr0.7Sr0.3)MnO3 phases, which may have contributed to the decrease of the activation polarization by decreasing the capacitance and increasing the number of active sites. After aging the high frequency EIS arcs/peaks shifted to a lower frequency range, and the low frequency arcs/peaks became unapparent compared to before aging.
A 3-D multiphysics finite element model was used to simulate the performance of the half cell SOFC. The effective exchange current density and the effective ionic conductivity of the cathodes showed much influence on the performance of the SOFC. Predicted and observed performance was compared.
Suggestions were given for the further experiments on the composite cathode.Ph. D.
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Larby, Line. « Development of Novel (Cu,Fe)3O4 Coatings for AISI 441 Solid Oxide Cell Interconnects : Coating optimization and long-term study ». Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-279130.
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As current environmental challenges are gaining increased attention, development of clean energy solutions is becoming one of the essential strategies to keep within the boundaries of established environmental policies. Solid oxide cell (SOC) technology can provide clean energy conversion and storage when hydrogen is the energy carrier. The high total energy conversion efficiency resulting from the high operation temperature of SOCs make the technology promising, but material costs must be reduced to make it commercially viable. Therefore, this thesis aims to study the long- term performance of a novel cost-optimized cell interconnect at 650 and 850 °C. At high temperatures, chromium evaporation from the interconnect result in electrode poisoning, which may be mitigated by application of a protective coating. The studied interconnect is an AISI 441 steel with some different pre-oxidized copper and iron spinel coatings. Sample analysis was made mainly with scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. It was found that the most promising pre-oxidation treatment was 24 h at 750 °C and that chromium migration was restrained at 650 °C long-term treatment but not at 850 °C where it wasfound available for evaporation at the surface.När samtida milljöutmaningar får ökad uppmärksamhet blir gröna energilösningar en av de viktigaste strategierna för att hålla sig inom satta gränser från etablerade miljöriktlinjer. Teknologin bakom fastoxidceller, eller solid oxide cells (SOCs), kan bidra med grön omvandling och lagring av energi när energibäraren är väte. Den höga totala omvandlingseffektiviteten, som kommer med den höga verkningstemperaturen, gör SOC till en lovande teknologi, men materialkostnaderna måste först reduceras innan den blir komersiellt gångbar. Därför syftar detta examensarbete till att undersöka prestandan av en ny, kostnadsoptimerad cellinterkonnektor på lång sikt i 650 och 850 °C. Vid höga temperaturer förångas krom från interkonnektorn, vilket leder till elektrodförgiftning, men kan mildras genom applicering av en skyddande beläggning. Den undersökta interkonnektorn är ett stål som betäcknas AISI 441 belagt med några olika föroxiderade beläggningar av koppar- och järnspinell. Proverna analyserades i huvudsak genom svepelektronmikroskopi kobinerat med energidispersiv röntgenspektroskopi och röntgendiffraktometri. Det visades att den mest lovande föroxideringsbehandlingen var 24 h i 750 °C och att krom förblev återhållet vid 650 °men inte vid 850 °C då det fanns tillgängligt för förångning vidytan.
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Sen, Firat. « Thermal Management Of Solid Oxide Fuel Cells By Flow Arrangement ». Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614496/index.pdf.
Texte intégralRésumé :
Solid oxide fuel cell (SOFC) is a device that converts the chemical energy of the fuel into the electricity by the chemical reactions at high temperatures (600-1000oC). Heat is also produced besides the electricity as a result of the electrochemical reactions. Heat produced in the electrochemical reactions causes the thermal stresses, which is one of the most important problems of the SOFC systems. Another important problem of SOFCs is the low fuel utilization ratio. In this study, the effect of the flow arrangement on the temperature distribution, which causes the thermal stresses, and the method to increase the fuel utilization, is investigated.
An SOFC single cell experimental setup is developed for Cross-Flow arrangement design. This setup and experimental conditions are modeled with Fluent®. The experimental results are used in order to validate and verify the model. The model results are found to capture with the experimental results closely. The validated model is used as a reference to develop the models for different flow arrangements and to investigate the effect of the flow arrangement on the temperature distribution. A method to increase the SOFC fuel utilization ratio is suggested. Models for different flow arrangements are developed and the simulation results are compared to determine the most advantageous arrangement.
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LeMasters, Jason Augustine. « Thermal Stress Analysis of LCA-based Solid Oxide Fuel Cells ». Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5220.
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This research characterizes the thermal stress resulting from temperature gradients in hybrid solid oxide fuel cells that are processed using a novel oxide powder slurry technology developed at Georgia Tech. The hybrid solid oxide fuel cell is composed of metallic interconnect and ceramic electrolyte constituents with integral mechanical bonds formed during high temperature processing steps. A combined thermo-mechanical analysis approach must be implemented to evaluate a range of designs for power output and structural integrity. As an alternative to costly CFD analysis, approximate finite difference techniques that are more useful in preliminary design are developed to analyze the temperature distributions resulting from a range of fuel cell geometries and materials. The corresponding thermal stresses are then calculated from the temperature fields using ABAQUS. This model analyzes the manufacturing, start-up, and steady state operating conditions of the hybrid solid oxide fuel cell.
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Lakshminarayanan, Nandita. « Investigation and development of electro catalysts for Solid Oxide Fuel Cells ». The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1291134392.
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Li, Xiaxi. « In situ characterization of electrochemical processes of solid oxide fuel cells ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54256.
Texte intégralRésumé :
Solid oxide fuel cells (SOFCs) represent a next generation energy source with high energy conversion efficiency, low pollutant emission, good flexibility with a wide variety of fuels, and excellent modularity suitable for distributed power generation. As an electrochemical energy conversion device, SOFC’s performance and reliability depend sensitively on the catalytic activity and stability of the electrode materials. To date, however, the development of electrode materials and microstructures is still based largely on trial-and-error methods because of inadequate understanding of the mechanisms of the electrode processes. Identifying key descriptors/properties of electrode materials or functional heterogeneous interfaces, especially under in situ conditions, may provide guidance to the design of electrode materials and microstructures. This thesis aims to gain insight into the electrochemical and catalytic processes occurring on the electrode surfaces using unique characterization tools with superior sensitivity, high spatial resolution, and excellent surface specificity applicable under in situ/operando conditions.
Carbon deposition on nickel-based anodes is investigated with in situ Raman spectroscopy and SERS. Analysis shows a rapid nucleation of carbon deposition upon exposure to small amount of propane. Such nucleation process is sensitive to the presence of surface coating (e.g., GDC) and the concentration of steam. In particular, operando analysis of the Ni-YSZ boundary indicates special function of the interface for coking initiation and reformation.
The coking-resistant catalysts (BaO, BZY, and BZCYYb) are systematically studied using in situ Raman spectroscopy, SERS, and EFM. In particular, time-resolved Raman analysis of the surface functional groups (-OH, -CO3, and adsorbed carbon) upon exposure to different gas atmospheres provides insight into the mechanisms related to carbon removal. The morphology and distribution of early stage carbon deposition are investigated with EFM, and the impact of BaO surface modification is evaluated.
The surface species formed as a result of sulfur poisoning on nickel-based anode are examined with SERS. To identify the key factors responsible for sulfur tolerance, model cells with welldefined electrode-electrolyte interfaces are systematically studied. The Ni-BZCYYb interface exhibits superior sulfur tolerance.
The oxygen reduction kinetics on LSCF, a typical cathode material of SOFC, is studied using model cells with patterned electrodes. The polarization behaviors of these micro- electrodes, as probed using a micro-probe impedance spectroscopy system, were correlated with the systematically varied geometries of the electrodes to identify the dominant paths for oxygen reduction under different electrode configurations. Effects of different catalyst modifications are also evaluated to gain insight into the mechanisms that enhance oxygen reduction activity.
The causes of performance degradation of LSCF cathodes over long term operation are investigated using SERS. Spectral features are correlated with the formation of surface contamination upon the exposure to air containing Cr vapor, H2O, and CO2. Degradation in cathode performance occurs under normal operating conditions due to the poisoning effect of Cr from the interconnect between cells and the high operating temperature. The surface-modified LSCF cathode resists surface reactions with Cr vapor that impairs electrode performance, suggesting promising ways to mitigate performance degradation.
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Schwartz, Brian. « Analysis of the potential for thermal radiation promotion within solid oxide fuel cells ». Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53909.
Texte intégralRésumé :
Solid oxide fuel cell (SOFC) systems have the potential to provide highly efficient power generation systems capable of utilizing readily available hydrocarbons. It is hoped that these systems will be capable of replacing some of the conventional power systems and act to reduce overall emissions and increase energy efficiency. SOFC technology faces many challenges such as high cost, lifetime uncertainties, and long startup times; and these challenges have prevented SOFC technology from being widely adopted.
Established methods for providing SOFC stack thermal management are either very costly, work against system design goals, or are unreliable. If SOFC thermal management needs could be reduced, it is possible that SOFC cost and lifetime could be improved. It is thought that promotion of thermal radiation within a SOFC stack may add thermal control which will reduce the need for stack thermal management. Radiation may be promoted by decreasing the length: hydraulic diameter ratio of cathode flow channels and by increasing the manifold size to create a larger stack radiation enclosure. Full thermal tests of a SOFC stack are difficult and expensive, and due to this simulations of a SOFC are widely used to analyze stack thermal behavior.
In this work, a model of a SOFC “unit cell” is adjusted to represent modern SOFC stacks. The proposed methods for radiation promotion are tested with simulations using this model, and conclusions of radiation promotion in SOFC stacks are provided. Additionally, radiative properties of commonly used materials are obtained through experiments, and future work for reducing stack reliance on active thermal management is proposed.
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Ovalle, Alejandro. « Manganese titanium perovskites as anodes for solid oxide fuel cells ». Thesis, St Andrews, 2008. http://hdl.handle.net/10023/567.
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Kaseman, Brian J. « An Investigation of Secondary Formations of High Temperature Solid Oxide Fuel Cells ». Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1330648584.
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Hyde, Andrew Justin. « A Portable Generator Incorporating Mini-Tubular Solid Oxide Fuel Cells ». The University of Waikato, 2008. http://hdl.handle.net/10289/2582.
Texte intégralRésumé :
Modern society has become reliant on battery powered electronic devices such as cell phones and laptop computers. The standard way of recharging these devices is by connecting to a reticulated electricity supply. In situations with no electricity supply some other recharging method is required. Such a possibility is a small, portable, generator based on fuel cell technology, specifically mini-tubular solid oxide fuel cells (MT-SOFC). MT-SOFCs have been developed since the 1990s but there is limited analysis, discussion or research on developing and constructing a portable generator based on MT-SOFC technology. Such a generator, running on a portable gas supply, requires combining the key aspects of cell performance, a heating and fuel reforming system, and cell manifolds. Cell design, fuel type, fuel flow rate, current-collection method and operating temperature all greatly affected MT-SOFCs performance. Segmenting the cathode significantly increased the power output. Maximum power density from an electrolyte supported MT-SOFC was 140 mW/cm2. The partial oxidation reactor (POR) developed provided the required heat to maintain the MT-SOFCs at an operating temperature suitable for generating electricity. The exhaust gas from the POR was a suitable fuel for MT-SOFCs, having sufficient carbon monoxide and hydrogen to generate electricity. Various manifold materials were evaluated including solid metal blocks and folded sheet metal. It was found that manifolds made from easily worked alumina fibre board decreased the thermal stresses and therefore the fracture rate of the MT-SOFCs. The final prototype developed comprised a partial oxidation reactor and MT-SOFCs mounted in alumina fibre board manifolds within a well-insulated enclosure, which could be run on LPG. Calculated efficiency of the final prototype was 4%. If all the carbon monoxide and hydrogen produced by the partial oxidation reactor were converted to electrical energy, efficiency would increase to 39%. Under ideal conditions, efficiency would be 78%. Efficiency of the prototype can be improved by increasing the fuel and oxygen utilisation ratios, ensuring heat from the exhaust gases is transferred to the incoming gases, and improving the methods for collecting current at both the anode and cathode.
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Price, Robert. « Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells ». Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16018.
Texte intégralRésumé :
Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
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Williams, Robert Earl Jr. « Simulation and Characterization of Cathode Reactions in Solid Oxide Fuel Cells ». Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16309.
Texte intégralRésumé :
In this study, we have developed a dense La0.85Sr0.15MnO3-δ (LSM) Ce0.9Gd0.1O1.95 (GDC) composite electrode system for studying the surface modification of cathodes. The LSM and GDC grains in the composite were well defined and distinguished using energy dispersive x-ray (EDX) analysis. The specific three-phase boundary (TPB) length per unit electrode surface area was systematically controlled by adjusting the LSM to GDC volume ratio of the composite from 40% up to 70%. The TPB length for each tested sample was determined through stereological techniques and used to correlate the cell performance and degradation with the specific TPB length per unit surface area.
An overlapping spheres percolation model was developed to estimate the activity of the TPB lines on the surface of the dense composite electrodes developed. The model suggested that the majority of the TPB lines would be active and the length of those lines maximized if the volume percent of the electrolyte material was kept in the range of 47 57%. Additionally, other insights into the processing conditions to maximize the amount of active TPB length were garnered from both the stereology calculations and the percolation simulations.
Steady-state current voltage measurements as well as electrochemical impedance measurements on numerous samples under various environmental conditions were completed. The apparent activation energy for the reduction reaction was found to lie somewhere between 31 kJ/mol and 41 kJ/mol depending upon the experimental conditions. The exchange current density was found to vary with the partial pressure of oxygen differently over two separate regions. At relatively low partial pressures, i0 had an approximately dependence and at relatively high partial pressures, i0 had an approximately dependence. This led to the conclusion that a change in the rate limiting step occurs over this range.
A method for deriving the electrochemical properties from proposed reaction mechanisms was also presented. State-space modeling was used as it is a robust approach to addressing these particular types of problems due to its relative ease of implementation and ability to efficiently handle large systems of differential algebraic equations. This method combined theoretical development with experimental results obtained previously to predict the electrochemical performance data. The simulations agreed well the experimental data and allowed for testing of operating conditions not easily reproducible in the lab (e.g. precise control and differentiation of low oxygen partial pressures).
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Iakovleva, Anastasia. « Study of novel proton conductors for high temperature solid oxide cells ». Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLC016/document.
Texte intégralRésumé :
L'objectif principal de ce travail était l'étude systématique de plusieurs groupes de matériaux conducteurs protoniques: Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), Ba₂Nb₁₋ₓY₁₊ₓO₆₋₅, et BaZr₀.₈₅Y₀.₁₅O₃₋₅ (BZY15). Nous avons développé une voie de synthèse pour chaque groupe de matériaux tels que le procédé de combustion sol-gel, la synthèse lyophilisation et le procédé de complexation de citrate-EDTA modifié des nanopoudres pures et des céramiques denses ont été obtenus après ces synthèses suives d'un processus de frittage classique. La structure et la composition des produits obtenues ont été caractérisées par diffraction des rayons X (XRD) et microscopie électronique à balayage (MEB). La variation de la conductivité en fonction de la température a été étudiée par spectroscopie d'impédance, ainsi que la dépendance en fonction de pO₂ et pH₂O. Pour la famille de Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), nous avons étudié l'influence de la nature et la quantité de dopant sur les propriétés structurales et électriques. Les résultats indiquent une solution solide possible jusqu'à 10% de taux du substituant. Selon les observations au MEB, la taille des grains est augmente le taux de substitution. En ce qui concerne les propriétés électriques, nous avons constaté une augmentation de la conduction avec le taux de substitution. Tous les composés présentent une bonne stabilité en milieu humide, sous hydrogène et CO₂. Dans le cas des matériaux Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅, les propriétés physico-chimiques des matériaux synthétisés ont été caractérisées par la diffraction des rayons X et par MEB. La taille moyenne des grains a considérablement augmenté avec l'augmentation du taux de Y³⁺. Les propriétés de conduction ont été légèrement améliorées avec la substitution partielle de niobium par l'yttrium. La stabilité de Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ composés a été étudiée sous différentes atmosphères et conditions. Les propriétés de conduction ionique restent modestes ce qui a été explique par des simulations de dynamique moléculaire. Enfin, nous avons étudié l'influence d'emploi d'un additif ZnO et NiO lors de la synthèse de BZY15, les adjuvants de frittage pouvant être utilisés pour abaisser la température de frittage. L'oxyde de zinc comme un adjuvant de frittage permet de diminuer de 300 °C la température de frittage et d'augmenter légèrement la conduction ioniqueThe main objective of the present work was the systematic study of several groups of materials: Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), Ba₂Nb₁₋ₓY₁₊ₓO₆₋₅, and BaZr₀.₈₅Y₀.₁₅O₃₋₅ (BZY15) as proton conductors. We developed a synthesis route for each group of materials such as sol-gel combustion method, freeze-drying synthesis and modified citrate-EDTA complexing method. Pure nanopowders and dense ceramics were obtained after these syntheses plus a classical sintering process. The structure and composition of the obtained products were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The temperature dependences of the conductivity were investigated by impedance spectroscopy as a function of pO₂ and pH₂O. For the family of Gd₃₋ₓMeₓGaO₆₋₅ (Me = Ca²+, Sr²+), we studied the influence of dopant nature and content on the structural and electrical properties. Results indicate that the substitution possible till 10 % of doping content. According to the SEM observations, the grain size is increased with increasing dopant content. Concerning electrical properties, we found an increase of conduction with increasing dopant content. All compounds present a good stability in humid, hydrogen and CO₂ containing atmosphere. In case of Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ materials, the physico-chemical properties of synthesized materials have been characterized by the XRD and SEM techniques. The average grain size increased significantly with increasing amount of Y³⁺. Conduction properties were slightly improved with the partial substitution of niobium by yttrium. The stability of Ba₂Y₁₊ₓNb₁₋ₓO₆₋₅ compounds was investigated under different atmospheres and conditions. The ionic conduction in this case is quite low, which has been explained by futher molecular dynamics simulations. Finally, we studied the influence of an ZnO and NiO additives on the sintering of BZY15, being these sintering aids used to lower the sintering temperature. Zinc oxide as a sintering aid lowers the sintering temperature by 300 °C and slightly increases the bulk and total conductivity of BZY15
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BOIGUES, MUNOZ CARLOS. « Computational Simulation of Solid Oxide Fuel Cells – Integrating numerical and experimental approaches ». Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242989.
Texte intégralRésumé :
Le celle a combustibile ad ossido solido (Solid Oxide Fuel Cells - SOFCs) sono una tecnologia promettente in grado di produrre potenza elettrica e termica con un’efficienza eccezionale. Tuttavia, è necessaria una comprensione più approfondita dei processi fisico-chimici che si verificano all’interno della cella per risolvere la maggior parte dei problemi di degradazione che attualmente impediscono la maturità della tecnologia. Un approccio sistematico e sinergico tra misure sperimentali, l’uso di strumenti di analisi e techniche innovative – con particolare attenzione alla deconvoluzione degli spettri di impedenza elettrochimica (Electrochemical Impedance Spectroscopy - EIS) mediante il metodo della distribuzione dei tempi di rilassamento (Distributed Relaxation Times - DRT) – e teoria modellistica ha dimostrato di essere importante per la stima dei parametri che descrivono le caratteristiche microstrutturali ed elettrochimiche di due tipi di SOFC planari anodo-supportate, una progettata per funzionare ad una temperatura intermedia (750ºC) e l’altra per farlo a bassa temperatura (650ºC). Un macro-modello CFD (Computational Fluid Dynamics) dei campioni testati, che incorpora i parametri ottenuti dalla procedura menzionata, è stato convalidato confrontando le curve di polarizzazione simulate con quelle sperimentali. Questo modello ha dimostrato di essere un valido strumento per ottimizzare la microstruttura delle celle e per stabilire le basi per analizzare gli effetti di potenziali fenomeni di degrado nella cella e, infine, prevedere la generazione di elettricità a lungo termine in condizioni di funzionamento predeterminate. Inoltre, un modello CFD di una cella di tipo tubolare all’interno di un generatore di potenza (cioè, stack SOFC) di 500 Wel ha permesso di apprezzare come un singolo elemento dello stack si comporta in condizioni operative quasi realistiche.Solid oxide fuel cell (SOFC) is a promising electrochemical technology that can produce electrical and thermal power with outstanding efficiencies, however, a more profound understanding of the physicochemical processes occurring within the cell is necessary to overcome most of the degradation issues currently impeding the maturity of the technology. A systematic synergetic approach between experimental measurements, the use of novel analysis tools and techniques – with special attention to the deconvolution of electrochemical impedance spectroscopy (EIS) spectra by means of the distribution of relaxation times (DRT) method – and modelling theory has proved to be instrumental for the estimation of parameters describing the microstructural and electrochemical properties of two types of planar anode-supported SOFCs, one designed to operate at intermediate temperatures (750ºC) and the other at low temperatures (650ºC). A comprehensive macro-scale computational fluid dynamics (CFD) model of the tested samples incorporating the aforementioned parameters has been validated by confronting the simulated polarization curves with the experimental ones. This model has demonstrated to be a compelling tool to optimize the microstructure of the cells whilst establishing the bases to monitor and analyse the effects of potential degradation phenomena in the cell and predict the electrical output of the cell in the long run under pre-determined operating conditions. Additionally, a CFD model of a tubular-type cell comprised in the power module (i.e. SOFC stack) of a characterised 500Wel power generator has enabled to appreciate how a singular element of the stack behaves under nearly realistic operating conditions.
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Gamble, Stephen R. « Reversible solid oxide fuel cells as energy conversion and storage devices ». Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2454.
Texte intégralRésumé :
A reversible solid oxide fuel cell (RSOFC) system could buffer intermittent electrical generation, e.g. wind, wave power by storing electrical energy as hydrogen and heat. RSOFC were fabricated by thermoplastic extrusion of (La₀.₈Sr₀.₂)₀.₉₅MnO[subscript(3−δ)] (LSM) ceramic support tubes, which were microstructurally stable with 55% porosity at 1350°C. A composite oxygen electrode of LSM-YSZ was applied, providing a homogeneous substrate for a 20 μm - 30 μm thick YSZ electrolyte. A dip-coated 8YSZ slurry, and a painted commercial 3YSZ ink gave sintered densities of 90% and nearly 100% at 1350°C, respectively. A porous NiO/YSZ fuel electrode was also painted on. A Ag/Cu reactive air braze was unsuccessful at forming a void-free joint between the RSOFC and a 316 stainless steel gas delivery tube, as the braze did not penetrate the oxidation layer on the steel. Two alumina-based ceramic cements failed to fully seal the cell to an alumina gas delivery tube, due to thermal expansion coefficient mismatches and porosity after curing. Therefore, the maximum open circuit voltage (OCV) obtained during RSOFC testing was 0.8 V at 440°C. LSM-YSZ symmetrical cell performance measurements with oxygen pressure showed a diffusion polarisation, which was assigned to dissociative adsorption and surface diffusion of oxygen species. A collaborative RSOFC system software model showed ohmic and activation losses dominated the RSOFC, and diffusion losses were insignificant. Pressurisation from 1 to 70 bar increased the RSOFC Nernst voltage by 11% at 900°C, and reduced the entropy of the gases, reducing heat production and increasing electrical efficiency. A 500 kg Sn/Cu phase change heat store prevented the system overheating. Over a 16 h discharge-charge RSOFC cycle in the range 5 mol.% - 95 mol.% hydrogen in steam, at 20.4 A per cell or 3250 A m⁻², the electrical energy storage efficiency was 64.4%.
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Kluczny, Maksymilian. « Synthesis and Electrochemical Evaluation of Perovskite related oxide for Active Cathode for Solid Oxide Fuel Cells (SOFCs) ». Thesis, KTH, Kemiteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-223612.
Texte intégralRésumé :
Solid oxide fuel cells are used as stationary power plants for electricity production. Despite having a very high efficiency of 90% they haven’t gained a world-wide commercial usage, due to their very high operating temperatures, and high production cost. However, there is a lot of ongoing research with the aim of developing intermediate-temperature solid oxide fuel cells (IT-SOFCs) that could operate at temperatures below 800°C. Cathodes are the most studied components of IT-SOFCs, since decreasing operating temperature results in slow oxygen reduction reaction(ORR) kinetics and large polarization losses. Perovskite related metal oxides have become very popular materials that could make suitable cathodes for IT-SOFCs. In this work an evaluation of several materials belonging to three different material groups have been studied: single layer perovskites, with a general formula of ABO3, double layer perovskites, with a general formula of AA’B2O6 and Ruddlesden-Popper phase, with a general formula of An+1BnO3n+1. Power generating capabilities of those materials have been studied on an electrolyte supported cell, cathode/LSGM9182/Ni-Fe. IR drop and overpotential of the cathode was measured and activation energy of the ORR for each material has been calculated. The double layer perovskite cobaltites offer a significant drop in overpotential, increase in conductivity compared to their single layer counterpart, while being able to generate significant amount of power. Ruddlesden-Popper phase materials offer the lowest activation energy values amongst the researched materials, but offer limited power generation values in the setup they were tested. Both of double layer perovskites and Ruddlesden-Popper based materials have opportunities for their performance to be improved.Fastoxidbränsleceller används som stationära kraftverk för elproduktion. Trots att de har en mycket hög effektivitet på 90% har de inte fått en världsomspännande kommersiell användning på grund av deras mycket höga driftstemperaturer och hög produktionskostnad. Det är emellertid mycket pågående forskning med sikte på att utveckla intermediär temperatur fastoxidbränsleceller (IT-SOFC) som kan fungera vid temperaturer under 800 ° C. Katod är de mest studerade komponenterna i IT-SOFC, eftersom minskad driftstemperatur resulterar i kinetik med långsam syrereduktion (ORR) och stora polarisationsförluster. Perovskite-relaterade metalloxider har blivit mycket populära material som kan göra lämpliga katoder för IT-SOFC. I detta arbete har en utvärdering av flera material som hör till tre olika materialgrupper studerats: singelskikt perovskiter, med en generell formel för ABO3, dubbelskikt perovskiter, med en generell formel av AA'B2O6 och Ruddlesden-Popper-fasen med en allmän formel för An + 1BnO3n + 1. Effektgenereringskapaciteten hos dessa material har studerats på en elektrolytbärbar cell, katod / LSGM9182 / Ni-Fe. IR-droppe och överpotential hos katoden mättes och aktiveringsenergin för ORR för varje material har beräknats. Dubbelskiktet perovskit koboltiter ger en signifikant minskning av överpotentialen, ökad ledningsförmåga jämfört med deras enkelskikt motpart, samtidigt som man kan generera betydande mängden kraft. Ruddlesden-Popper-fasmaterial erbjuder de lägsta aktiveringsenergivärdena bland de undersökta materialen, men erbjuder begränsade kraftproduktionsvärden i den inställning de testades. Både av dubbelskiktet perovskiter och Ruddlesden-Popper-baserade material har möjligheter att förbättra deras prestanda.
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Aman, Amjad. « Numerical Simulation of Electrolyte-Supported Planar Button Solid Oxide Fuel Cell ». Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5101.
Texte intégralRésumé :
Solid Oxide Fuel Cells are fuel cells that operate at high temperatures usually in the range of 600oC to 1000oC and employ solid ceramics as the electrolyte. In Solid Oxide Fuel Cells oxygen ions (O2-) are the ionic charge carriers. Solid Oxide Fuel Cells are known for their higher electrical efficiency of about 50-60% [1] compared to other types of fuel cells and are considered very suitable in stationary power generation applications. It is very important to study the effects of different parameters on the performance of Solid Oxide Fuel Cells and for this purpose the experimental or numerical simulation method can be adopted as the research method of choice. Numerical simulation involves constructing a mathematical model of the Solid Oxide Fuel Cell and use of specifically designed software programs that allows the user to manipulate the model to evaluate the system performance under various configurations and in real time. A model is only usable when it is validated with experimental results. Once it is validated, numerical simulation can give accurate, consistent and efficient results. Modeling allows testing and development of new materials, fuels, geometries, operating conditions without disrupting the existing system configuration. In addition, it is possible to measure internal variables which are experimentally difficult or impossible to measure and study the effects of different operating parameters on power generated, efficiency, current density, maximum temperatures reached, stresses caused by temperature gradients and effects of thermal expansion for electrolytes, electrodes and interconnects. Since Solid Oxide Fuel Cell simulation involves a large number of parameters and complicated equations, mostly Partial Differential Equations, the situation calls for a sophisticated simulation technique and hence a Finite Element Method (FEM) multiphysics approach will be employed. This can provide three-dimensional localized information inside the fuel cell. For this thesis, COMSOL Multiphysics version 4.2a will be used for simulation purposes because it has a Batteries & Fuel Cells module, the ability to incorporate custom Partial Differential Equations and the ability to integrate with and utilize the capabilities of other tools like MATLAB, Pro/Engineer, SolidWorks. Fuel Cells can be modeled at the system or stack or cell or the electrode level. This thesis will study Solid Oxide Fuel Cell modeling at the cell level. Once the model can be validated against experimental data for the cell level, then modeling at higher levels can be accomplished in the future. Here the research focus is on Solid Oxide Fuel Cells that use hydrogen as the fuel. The study focuses on solid oxide fuel cells that use 3-layered, 4-layered and 6-layered electrolytes using pure YSZ or pure SCSZ or a combination of layers of YSZ and SCSZ. A major part of this research will be to compare SOFC performance of the different configurations of these electrolytes. The cathode and anode material used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively.ID: 031001387; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: .; Title from PDF title page (viewed May 22, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 101-107).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermofluids
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Tang, Shijie. « Development of Multiphase Oxygen-ion Conducting Electrolytes for Low Temperature Solid Oxide Fuel Cells ». Scholarly Repository, 2007. http://scholarlyrepository.miami.edu/oa_theses/112.
Texte intégralRésumé :
One of the major trends of development of solid oxide fuel cells is to reduce the operating temperature from the high temperature range (>950°C) and intermediate temperature range (750-850°C) to the low temperature range (450-650°C). Development of low temperature oxygen ion conducting electrolytes is focused on single-phase materials including Bi2O3 and CeO2-based oxides. These materials have high ion conductivity at the low temperature range, but they are unstable in reducing environments and they are also electronic conductors. In the present research, three types of multiphase materials, Ce0.887Y0.113O1.9435 (CYO)-ZrO2, CYO- yttria-stabilized zirconia (YSZ), and CuO-CYO were investigated. We found that the conductivity of multiphase electrolyte CuO-CYO with a mass ratio of 1:3 is at least 4 times greater than that of CYO and 10 times greater than that of YSZ, the most commonly used material, obtained in the present experiments at 600°C. The enhancement of conductivity in multiphase materials correlates with the level of mismatch between the two phases. Large mismatches in terms of valance and structure result in high vacancy density and hence high oxygen ion conductivity at grain boundaries. This study demonstrates that synthesis of multiphase ceramic materials is a feasible new avenue for development of oxygen ion electrolyte material for low temperature SOFCs.
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Kearney, Jonathan. « Cu/CeₓZr(₁₋ₓ)O₂ catalysts for solid oxide fuel cell anodes ». Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1845.
Texte intégralRésumé :
Ce[subscript(x)]Zr[subscript(1-x)]O₂ mixed oxides of varying compositions were prepared by a sol-gel citrate complexion technique. In order to improve the catalytic activity of the oxides they were impregnated with copper using two different impregnation techniques. The bare oxides and copper impregnated samples were investigated using a range of Temperature Programmed (TP) techniques, in an attempt to establish their effectiveness as anode materials for solid oxide fuel cells (SOFCs) run on hydrocarbon fuels. In order to conduct the TP experiments a novel system was designed and constructed. The high Ce containing mixed oxides were shown to be reduced at lower temperature than high Zr content samples. TPRx experiments were employed to investigate which of the oxides was most prone to carbon deposition when reacted in methane, with the high ceria sample displaying the lowest level of carbon deposition. Lightoff experiments were undertaken to establish which oxide composition was the most active for methane oxidation. The activity of the oxides increased with ceria content up to 75 mole% (ZCe75), before decreasing for ZCe90. All the mixed oxides were shown to be more active for methane oxidation than CeO₂.
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Kosinski, Marcin Robert. « Nanomaterials for solid oxide fuel cell electrolytes and reforming catalysts ». Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2588.
Texte intégralRésumé :
In this work, a broad range of analytical methods was applied to the study of the following three materials systems: yttria-stabilised zirconia (YSZ), samarium-doped ceria (SDC) and SDC-supported metal catalysts. YSZ and SDC were studied in the light of their application as solid electrolytes in Solid Oxide Fuel Cells. The SDC-supported metal catalysts were evaluated for application in the reforming of methanol. The conductive properties of YSZ pellets derived from powders of different Y contents and particle size ranges were investigated using Impedance Spectroscopy (IS). Comparative studies of the crystallography (by X-ray Powder Diffraction (XRD)), morphology (by Scanning and Transmission Electron Microscopy (SEM, TEM)), chemical composition (by Energy Dispersive X-ray Spectroscopy (EDX) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS)) and sintering behaviour (dilatometry) were employed in the overall assessment of the conductivity results collected. Detailed studies of three SDC compositions were performed on nanopowders prepared by a low temperature method developed in the Baker group. Modifications led to a simple and reliable method for producing high quality materials with crystallites of ~10 nm diameter. The products were confirmed by XRD and TEM to be single-phase materials. Thermogravimetric analysis, dilatometry, specific surface area determination, elemental analysis and IS were carried out on these SDC powders. The relationships between particle size, chemical composition, sintering conditions and conductivity were studied in detail allowing optimum sintering conditions to be identified and ionic migration and defect association enthalpies to be calculated. Finally, the interesting results obtained for the SDC nanopowders were a driving force for the preparation of SDC-supported metal catalysts. These were prepared by three different methods and characterised in terms of crystallographic phase, specific surface area and bulk and surface chemical composition. Isothermal catalytic tests showed that all catalysts had some activity for the reforming of methanol and that some compositions showed both very high conversions and high selectivities to hydrogen. These catalysts are of interest for further study and possibly for commercial application.
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Zivak, Milica. « Studying the Effects of Siloxanes on Solid Oxide Fuel Cell Performance ». Youngstown State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1588956037196142.
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McCoppin, Jared Ray. « Fabrication and Analysis of Compositionally Graded Functional Layers for Solid Oxide Fuel Cells ». Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1292631552.
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Gardner, Paul. « Aerosol Jet Printing of LSCF-CGO Cathode for Solid Oxide Fuel Cells ». Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1316166020.
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Sivasankaran, Visweshwar. « Manufacturing and characterization of single cell intermediate-temperature solid oxide fuel cells for APU in transportation application ». Thesis, Dijon, 2014. http://www.theses.fr/2014DIJOS027/document.
Texte intégralRésumé :
La fabrication de cellules de piles à combustible IT-SOFC de large dimension par un nouveau procédé simple et peu coûteux est présentée dans ce manuscrit. L’optimisation de ce nouveau procédé en regard de l’utilisation d’agents de porosité, d’épaisseur de couches et de température de frittage a été réalisée. Les résultats des tests électrochimiques sur des cellules de surface active 10 cm2 réalisés dans le dispositif Fiaxell semi-ouvert ont été détaillés pour différentes cellules. Des tests de performance de longue durée ont également été menés sur le dispositif Fiaxell, présentés et discutés. La préparation et la réalisation d’un nouveau banc de test de stack a également été mené et présenté dans ces travauxThe fabrications of large area IT-SOFC planar cell by new simple and cost effective process were explained. The optimization of the new process with respect to pore formers, thickness of layers, sintering temperature were performed. The electrochemical results of 10cm2 performed in Fiaxell open flange set up were detailed with respect to different configuration. Long term ageing performance tests of single cells were conducted in Fiaxell device and results are discussed. Preparation of new test bench and stacking process performed till now were briefed
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ORTIGOZA, VILLALBA GUSTAVO ADOLFO. « DESIGN & ; DEVELOPMENT OF PLANAR SOLID OXIDE FUEL CELL STACK ». Doctoral thesis, Politecnico di Torino, 2013. http://hdl.handle.net/11583/2507927.
Texte intégralRésumé :
In the present work, planar anode-supported Solid Oxide Fuel Cell short-stacks have been designed, assembled, tested and characterized.
The design of the stacks and its components (frame, housing, interconnect, compressive and bonded seals) required a great attention to the materials properties (i.e. thermal expansion coefficient compatibility, durability, strength and oxidation resistance, conductivity and so on), as well as to the fluid-dynamic analysis focused on flow field and gas distribution. Then, a careful analysis was done based on a multidisciplinary approach to select the stack components materials, geometries, and dimensions; in order to assure a high performing stack at elevated temperatures with cost reduction of materials, parts manufacturing and assembly procedure.
The materials selected were: Crofer®22APU for the interconnect and the frame; AISI 316L for bolts and housing; Thermiculite® 866 for the compressive seal placed between the frame and the interconnect plate; Flexible Mica Paper for the compressive seal positioned between the interconnect endplate and the housing; SiO2-CaO-Al2O3-Na2O glass-ceramic sealant for the bonded seal to join the frame with the cell.
On the other hand, the stack assembly was focused on the implementation of innovative and simple procedures, which allowed power capacity scale-up in accordance to power requirements. In this work, two different stack configurations were produced: with one cell (for initial testing of the materials and fluid-dynamic selected solutions) and with three cells. It must be mentioned that all developed stacks in this research were assembled with commercial cells “ASC3” from H.C. Starck.
Also, calculations at ambient temperature and 800°C were done in the stack compression system to determine the proper tightening torque to be applied: this value was 50N. Although this calculation took into consideration the loss of tightening torque at high temperatures, some marks were found in housing and micas during the stack inspection after disassembly. These marks are a clear indicator of gas leakage.
Additionally, a study was carried out related to the effect of the protective Mn1.5Co1.5O4 coating deposited on interconnect surface to prevent the cathode Cr poisoning. This experiment was executed in the stack of one cell configuration. No voltage degradation was observed during the galvanostatic experiment of 360 h at 800°C.
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Woodward, Heather Kathleen. « A performance based, multi-process cost model for solid oxide fuel cells ». Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0428103-235205.
Texte intégralRésumé :
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: Solid oxide fuel cell; SOFC; cost model; sputtering; tape casting; screen printing; performance model; process yield model. Includes bibliographical references (p. 93).
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Garbujo, Alberto. « Perovskite materials as electrodes for solid oxide fuel cells active toward sustainable reactions ». Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3421824.
Texte intégralRésumé :
Traditional solid oxide fuel cell (SOFC) work between 800 °C and 1000 °C but this induces great materials deterioration and a high device cost. The development of new electrodes for SOFC application, characterized by high activity at intermediate temperatures (600-800 °C), is extremely important for the commercial diffusion and the future of this technology.
In this research advanced perovskite materials were studied as electrodes for Solid Oxide fuel cell application. Particular attention was paid to their activity toward sustainable reaction (methane oxidation and dry reforming) and the design of material avoiding platinum group elements and minimizing rare earth elements. The methane was chosen due to its role as bio-fuel in the carbon footprint decrease (bio gas, CH4 and CO2).
Two different perovskite-based materials have been studied for SOFC application, titanates and cobaltites. All samples were prepared by means citric method and deeply characterized by XRD, XPS, TPR, TPO, BET, SEM and EIS. The catalytic activities toward methane (reforming and oxidation) were detected by GC.
Among titanates (SrTiO3 doped with Mo or Fe ) only SrTi0.9Mo0.1O3 infiltrated with 15%wt shown a good activity toward dry reforming (58% of CH4 conversion at 800 °C) with an interesting polarisation resistance observed, 1.57 Ω cm2 at 800°C under 5% of H2/Ar.
(LaSr)Co0.5M0.5O4 (M = Cu, Ni) Ruddlesden Popper type cobaltites were investigated as electrodes for symmetric solid oxide fuel cell. The best catalytic activity was observed on (LaSr)2Co0.5Ni0.5O4 achieving 80% of CH4 conversion at 800 °C in methane oxidation. The electrochemical behaviour of (LaSr)2Co0.5Ni0.5O4 was tested under air (cathode) and under 5% CH4/Ar (anode) conditions showing a polarization resistance of 0.56 Ω cm2 and 0.94 Ω m2 at 800 °C respectively.
In order to go deeper inside the performance of these materials, both in term of MIEC and of catalytic activity, in situ time resolved high energy X-ray diffraction analysis was carried out to deeply investigate the structural changes of Co-based perovskite under pulsing conditions. The experiments were executed at European synchrotron radiation facility (ESRF) in Grenoble. The high reversibility observed on Co-based perovskites have revealed the potential of these materials encouraging further studies on more complex systems for symmetric and reversible SOFC application. The data collected give useful information on structural change involved into catalytic activity.La tradizionale cella a combustibile ad ossido solido (SOFC) lavora tra gli 800 °C e i 1000 °C, tuttavia questa condizione induce un notevole deterioramento ed un conseguente aumento dei costi dei materiali. Lo sviluppo di nuovi materiali elettrodici per applicazioni SOFC, caratterizzati da un’alta attività a temperature intermedie (600-800 °C), è estremamente importante per la commercializzazione e il futuro di questa tecnologia. In questa ricerca, materiali perovskitici avanzati sono stati studiali come elettrodi per celle a combustibili ad ossido solido. Particolare attenzione è stata posta alla loro attività verso reazioni sostenibili (l’ossidazione e il reforming del metano) e alla formulazione di materiali privi di elementi del gruppo del platino e minimizzando la quantità di terre rare. Il metano è stato scelto grazie il suo ruolo come bio-combustibile nella diminuzione dell’impronta del carbonio (bio-gas, CH4 e CO2). Due tipi differenti di materiali perovskitici sono stati studiati per applicazioni SOFC, i titanati e i cobaltiti. Tutti i materiali sono stati preparati tramite il metodo dei citrati e caratterizzati con XRD, XPS, TPR, TPO, BET, SEM e EIS. Le attività catalitiche verso il metano (reforming e ossidazione) sono state misurate attraverso il GC. Tra i titanati studiati (SrTiO3 sostituito con Mo o Fe) solo SrTi0.9Mo0.1O3 infiltrato con il 15% wt ha mostrato una buona attività verso il reforming del metano (58% della conversione di CH4 a 800 °C) con un interessante resistenza di polarizzazione pari a 1.57 Ω cm2 a 800°C sotto flusso di 5% H2/Ar. I cobaltiti con struttura tipo Ruddlesden Popper, (LaSr)Co0.5M0.5O4 (M = Cu, Ni), sono stati invece studiati come elettrodi per SOFC simmetriche. La migliore attività catalitica è stata osservata su (LaSr)Co0.5Ni0.5O4 raggiungendo una conversione del 80% di CH4 a 800 °C nell’ossidazione del metano. Il comportamento elettrochimico di (LaSr)Co0.5M0.5O4 è stato testato in aria (catodo) e sotto flusso di 5% di metano (anodo) mostrando una resistenza di polarizzazione di 0.56 Ω cm2 e 0.94 Ω m2 a 800 °C rispettivamente. Al fine di andare a fondo sulle performance di questi materiali, sia in termini di MIEC che di attività catalitica, analisi di raggi X ad alta energia in situ e risolte nel tempo sono state condotte per analizzare i cambiamenti strutturali delle perovskiti a base di cobalto sotto condizioni impulsate. Gli esperimento sono stati condotti al European synchrotron radiation facility (ESRF) a Grenoble. L’alta reversibilità osservata nei cobaltiti ha rivelato il potenziale di questi materiali incoraggiando ulteriori studi su sistemi più complessi per celle SOFC simmetriche e reversibili. I dati raccolti hanno prodotto informazioni preziose sui cambi strutturali che avvengono durante l’attività catalitica.
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Green, Christopher K. « Development of Model for Solid Oxide Fuel Cell Compressive Seals ». Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19696.
Texte intégralRésumé :
Fuel cells represent a promising energy alternative to the traditional combustion of fossil fuels. In particular, solid oxide fuel cells (SOFCs) have been of interest due to their high energy densities and potential for stationary power applications. One of the key obstacles precluding the maturation and commercialization of planar SOFCs has been the absence of a robust sealant. A leakage computational model has been developed and refined in conjunction with leakage experiments and material characterization tests at Oak Ridge National Laboratory to predict leakage in a single interface metal-metal compressive seal assembly as well as multi-interface mica compressive seal assemblies. The composite model is applied as a predictive tool for assessing how certain parameters (i.e., temperature, applied compressive stress, surface finish, and elastic thermo physical properties) affect seal leakage rates.
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Cooper, Matthew E. « Energy Production from Coal Syngas Containing H2S via Solid Oxide Fuel Cells Utilizing Lanthanum Strontium Vanadate Anodes ». Ohio University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1219867679.
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Koslowske, Mark T. « A process based cost model for multi-layer ceramic manufacturing of solid oxide fuel cells ». Link to electronic thesis, 2003. http://www.wpi.edu/Pubs/ETD/Available/etd-0810103-173353.
Texte intégralRésumé :
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: process based cost model; cost model; fuel cell; PBCM; multi-layer ceramics; sofc; solid oxide fuel cell. Includes bibliographical references.
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Ricca, Chiara. « Combined theoretical and experimental study of the ionic conduction in oxide-carbonate composite materials as electrolytes for solid oxide fuel cells (SOFC) ». Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066623/document.
Texte intégralRésumé :
Les composites oxyde-carbonate pourraient constituer des électrolytes pour les SOFC fonctionnant entre 400-600°C car ils attendent une conductivité de 0,1 S/cm à 600°C. Une meilleure compréhension de l'origine de leurs performances est à ce jour nécessaire. Pour y parvenir, une approche combinée théorique et expérimentale a été développée. La conductivité, mesurée à travers la SIE, a été étudiée en fonction de la phase oxyde ou carbonate et de l'atmosphère de travail. Les résultats sur les composite de CeO2 ou YSZ ont montré que seule l'interface peut expliquer des observations surprenantes. De la réactivité a été observée dans le cas des composites à base de TiO2. On a donc proposé une stratégie computationnelle qui utilise des calculs DFT périodiques: la structure du bulk de chaque phase a d'abord été étudiée afin de trouver un bon protocole computationnel, qui a été ensuite utilisé pour identifier un modèle pour la surface la plus stable des deux phases. Ces modèles de surfaces ont donc été combinés pour obtenir un modèle de l'interface oxyde-carbonate, utilisable comme structure de départ pour des calculs DFT et de DM. Cette stratégie a permis d'obtenir des informations sur structure, stabilité et propriétés électroniques des composites. YSZ-LiKCO3 a été utilisé pour mieux comprendre l'effet des interfaces sur le transport de différentes espèces, tandis que le modèle de l'interface entre TiO2 et LiKCO3 a été utilisé pour étudier la réactivité entre ces deux matériaux. Finalement, ces résultats ouvrent la voie vers une plus grande compréhension des principes de fonctionnement des SOFC basées sur les électrolytes composites oxyde-carbonateOxide-carbonate composites are promising electrolytes for LT-SOFC, thanks to their high conductivity (0.1-1 S/cm at 600°C). A deeper understanding on the origins of their improved performances is still necessary. For this purpose, a combined theoretical and experimental approach was developed. We first studied systematically the conductivity of the material, measured through EIS, as a function of different oxide or carbonate phases and of the operating atmosphere. Results on YSZ- and CeO2-based materials indicate that by only taking into account the interfaces it is possible to rationalize some surprising observations, while reactivity issues have been observed for TiO2-carbonate composites. We then proposed a computational strategy based on periodic DFT calculations: we first studied the bulk structure of each phase so as to select an adequate computational protocol, which has then been used to identify a suitable model of the most stable surface for each phase. These surface models have thus been combined to obtain a model of the oxide-carbonate interface that through static DFT and MD provides a deeper insight on the interface at the atomic level. This strategy was applied to provide information on the structure, stability and electronic properties of the interface. YSZ-LiKCO3 was used as a case study to investigate the conduction mechanisms of different species. Results showed a strong influence of the interfaces on the transport properties. The TiO2-LiKCO3 model was, instead, used to investigate the reactivity of these materials. Overall, these results pave the way toward a deeper understanding of the basic operating principles of SOFC based on these materials
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Sun, Shichen. « Electrochemical Behaviors of the Electrodes for Proton Conducting Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) ». FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3915.
Texte intégralRésumé :
Proton conducting intermediate temperature (600oC-400oC) solid oxide fuel cells (IT-SOFC) have many potential advantages for clean and efficient power generation from readily available hydrocarbon fuels. However, it still has many unsolved problems, especially on the anode where the fuel got oxidized and the cathode where oxygen got reduced. In this study, for the anode, the effects of hydrogen sulfite (H2S) and carbon dioxide (CO2) as fuel contaminants were studied on the nickel (Ni) based cermet anode of proton conducting IT-SOFC using proton conducting electrolyte of BaZr0.1Ce0.7Y0.1Yb0.1O3 (BZCYYb). Both low-ppm level H2S and low-percentage level CO2 caused similar poisoning effects on the anode reaction. The H2S poisoning effect was also found to be much less than on oxide-ion conducting SOFC, which is attributed to the absence of water evolution for the anode reaction in proton conducting SOFC. In addition, the H2S/CO2 poisoning mechanisms were investigated using X-ray diffraction, energy dispersive spectroscopy (EDS), Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). For H2S, other than possible sulfur dissolution into BZCYYb, no bulk reaction was found, suggesting sulfur adsorption contributes to the reduced performance. For CO2, reaction with BZCYYb to form BaCO3 and CeO2 is identified and is believed to be the reason for the sudden worsening in CO2 poisoning as temperature drops below ~550oC. For the cathode, several representative SOFC cathodes including silver (Ag), La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), LSCF-BZCYYb composite, and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) were evaluated based on BZCYYb electrolyte. LSCF give similar high interfacial resistance as Ag, while LSCF-BZCYYb composite cathode shows lower interfacial resistance, suggesting LSCF behaves like pure electronic conductor cathode in this case. For BSCF, it shows smallest interfacial resistance and the charge transfer process appears to accelerate with the introduction of H2O, while oxygen adsorption/transport seem to slow down due to adsorbed H2O. Furthermore, CO2 was shown to cause poisoning on the BSCF cathode, yet the poisoning was significantly reduced with the co-presence of water. The results suggest that although BSCF seem to display mixed proton-electronic conduction, its strong affinity to H2O may inhibit the oxygen reduction reaction on the cathode and new cathode materials still need to be designed.
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Khan, Feroze. « Effect of Hydrogen Sulfide in Landfill Gas on Anode Poisoning of Solid Oxide Fuel Cells ». Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1338838003.
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DE, MIRANDA AURISTELA CARLA. « Design, production and characterization of glass-ceramic based sealants for solid oxide fuel cells applications ». Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2591557.
Texte intégralRésumé :
Planar solid oxide fuel cells (SOFCs) are capable of achieving higher power density than tubular SOFC, but hermetic seals are required to prevent mixing of the fuel and oxidant, It is still a challenge to develop sealing materials that retain desirable physical properties, are chemically compatible with other fuel cell components at high temperature (e.g. 800 °C) in a wide range of oxygen partial pressure, and remain operational over thousands of hours. In most planar SOFCs stacks designs, the interconnect is sealed to the cell components. The seal between the metal interconnect and the ceramic SOFCs components presents a challenge. Design, development and implementation of reliable sealants may contribute to the destiny of SOFC electrical power-generation technology. Glass–ceramics, which can be prepared by controlled sintering and crystallization of glasses, possess superior mechanical properties and higher viscosity at the SOFC operating temperature than glasses. The application of a protective coating on the alloy surface has been proven as a practical and effective method to reduce corrosion rates and/or inhibit Cr volatilization and thus cathode poisoning. Though some coatings can be highly effective in reducing corrosion rates and reducing area specific resistance of metallic interconnects, their properties for blocking chromium diffusion are limited and need more research on advanced materials and new processing methods.
Furthermore, in the complex contest of the SOFC stack, the interconnect/sealant interface plays a key role in the stack reliability, efficiency and durability that depends also on the gas tightness provided by seals during SOFC operation for thousands of hours. It is desirable that reactions between the sealant and the coating or the metallic interconnect are limited during SOFC relevant operating conditions, otherwise spallation and detachments at the interfaces can occur and determine leakage and SOFC degradation.
Finally, different approaches are used in this work for the integration (i. e. joining) of ceramic and metallic components in solid oxide fuel cells (SOFCs) stacks, where dissimilar materials have to be joined and sealed for a reliable long-term operation. In particular, the thermo-mechanical compatibility of sealants with other stack components critically influence the reliability and the robustness of SOFCs devices.
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Lynch, Matthew Earl. « Modeling, simulation, and rational design of porous solid oxide fuel cell cathodes ». Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45852.
Texte intégralRésumé :
This thesis details research performed in modeling, simulation, and rational design of porous SOFC cathodes via development, extension, and use of the key tools to aid in the fundamental understanding and engineering design of cathode materials. Phenomenological modeling of triple phase boundary (TPB) reactions and surface transport on La₁₋ₓSrₓMnO₃ (LSM) was conducted, providing insight into the role of the bulk versus surface oxygen reduction pathway and the role of sheet resistance in thin-film patterned electrode measurements. In response to observation of sheet resistance deactivation, a modeling study was conducted to design thin-film patterned electrodes with respect to sheet resistance. Additionally, this thesis outlines the application of phenomenological chemical kinetics to describe and explain the performance and stability enhancements resulting from surface modification of La₁₋ₓSrₓCo₁₋yFeyO₃₋delta (LSCF) with a conformal LSM coating. The analysis was performed in close coordination with electrochemical experiments and transmission electron microscopy. Finally, the thesis describes conformal modeling of porous cathode microstructures using chemical kinetics and transport models. A novel application of conservative point defect ensembles was developed to allow simulations with complicated chemical surface kinetics to be efficiently coupled with bulk transport within the porous structure. The finite element method was employed to simulate electrochemical response conformal to sintered porous ceramic structures using actual 3D microstructural reconstructions obtained using x-ray microtomography. Mesh refinement, linear, and nonlinear reaction rate kinetics were employed to study the bulk versus surface oxygen reduction pathways and the effect of near-TPB nanostructure.
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Lu, Lanying. « Studies of anode supported solid oxide fuel cells (SOFCs) based on La- and Ca-Doped SrTiO₃ ». Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/7068.
Texte intégralRésumé :
Solid oxide fuel cells (SOFCs) have attracted much interest as the most efficient electrochemical device to directly convert chemical energy to usable electrical energy. The porous Ni-YSZ anode known as the state-of-the-art cermet anode material is found to show serious degradation when using hydrocarbon as fuel due to carbon deposition, sulphur poisoning, and nickel sintering. In order to overcome these problems, doped strontium titanate has been investigated as a potential anode material due to its high electronic conductivity and stability in reducing atmosphere. In this work, A-site deficient strontium titanate co-doped with lanthanum and calcium, La₀.₂Sr₀.₂₅Ca₀.₄₅TiO₃ (LSCT[sub](A-)), was examined. Flat multilayer ceramics have been produced using the aqueous tape casting technique by controlling the sintering behaviour of LSCT[sub](A-), resulting in a 450µm thick porous LSCT[sub](A-) scaffold with a well adhered 40µm dense YSZ electrolyte. Impregnation of CeO₂ and Ni results in a maximum power density of 0.96Wcm⁻² at 800°C, higher than those of without impregnation (0.124Wcm⁻²) and with impregnation of Ni alone (0.37Wcm⁻²). The addition of catalysts into LSCT[sub](A-) anode significantly reduces the polarization resistance of the cells, suggesting an insufficient electrocatalytic activity of the LSCT[sub](A-) backbone for hydrogen oxidation, but LSCT[sub](A-) can provide the electronic conductivity required for anode. Later, the cells with the configuration of LSCT[sub](A-)/YSZ/LSCF-YSZ were prepared by the organic tape casting and impregnation techniques with only 300-m thick anode as support. The effects of metallic catalysts in the anode supports on the initial performance and stability in humidified hydrogen were discussed. The nickel and iron impregnated LSCT[sub](A-) cell exhibits a maximum powder density of 272mW/cm² at 700°C, much larger than 43mW/cm² for the cell without impregnation and 112mW/cm² for the cell with nickel impregnation. Simultaneously, the bimetal Ni-Fe impregnates have significantly reduced the degradation rates in humidified hydrogen (3% H₂O) at 700°C. The enhancement from impregnation of the bi-metal can possibly be the result of the presence of ionic conducting Wustite Fe₁₋ₓO that resides underneath the Ni-Fe metallic particles and better microstructure. Third, in order to improve the ionic conductivity of the anode support and increase the effective TPBs, ionic conducting ceria was impregnated into the LSCT[sub](A-) anode, along with the metallic catalysts. The CeO₂-LSCT[sub](A-) cell shows a poor performance upon operation in hydrogen atmosphere containing 3% H₂O; and with addition of metallic catalysts, the cell performance increases drastically by almost three-fold. However, the infiltrated Ni particles on the top of ceria layer cause the deposition of carbon filament leading to cell cracking when exposure to humidified methane (3% H₂O). No such behaviour was observed on the CeO₂-NiFe impregnated anode. The microstructure images of the impregnated anodes at different times during stability testing demonstrate that the grain growth of catalysts, the interaction between the anode backbone and infiltrates, and the spalling of the agglomerated catalysts are the main reasons for the performance degradation. Fourth, the YSZ-LSCT[sub](A-) composites including the YSZ contents of 5-80wt.% were investigated to determine the percolation threshold concentration of YSZ to achieve electronic and ionic conducting pathways when using the composite as SOFC anode backbone. The microstructure and dilatometric curves show that when the YSZ content is below 30%, the milled sample has a lower shrinkage than the unmilled one due to the blocking effect from the well distributed YSZ grains within LSCT[sub](A-) bulk. However, at the YSZ above 30% where two phases start to form the individual and interconnected bulk, the composites without ball milling process show a lower densification. The impact of YSZ concentration and ball milling process on the electrical properties of the composites reveals that the percolation threshold concentration is not only dependant on the actual concentration, but also related to the local arrangement of two phases. In Napier University, the electroless nickel-ceramic co-depositon process was investigated as a manufacturing technique for the anodes of planar SOFCs, which entails reduced costs and reduced high-temperature induced defects, compared with conventional fabrication techniques. The Ni-YSZ anodes prepared by the electroless co-deposition technique without the addition of surfactant adhere well to the YSZ electrolyte before and after testing at 800°C in humidified hydrogen. Ni-YSZ anodes co-deposited with pore-forming starch showed twice the maximum power density compared with those without the starch. It has therefore been demonstrated that a porous Ni-YSZ cermet structure was successfully manufactured by means of an electroless plating technique incorporating pore formers followed by firing at 450°C in air. Although the use of surfactant (CTAB) increases the plating thickness, it induces the formation of a Ni-rich layer on the electrolyte/anode interface, leading to the delamination of anode most likely due to the mismatched TECs with the adjacent YSZ electrolyte.
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Corre, Gaël Pierre Germain. « Studies of alternatives anodes and ethanol fuel for SOFCs ». Thesis, University of St Andrews, 2009. http://hdl.handle.net/10023/841.
Texte intégralRésumé :
This thesis explores the development of efficient engineered composite alternative anodes and the use of ethanol as a fuel for Solid Oxide Fuel Cells. SOFCs can in theory operate with fuels other than hydrogen. However, this requires the design of efficient alternative anode material that do not catalyze carbon formation and that are tolerant to redox cycles. An innovative concept has been developed that relies on the impregnation of perovskites into porous YSZ structures to form the anode functional layer. Catalysts are added to provide sufficient catalytic activity. Cells with anodes containing LSCM and Ce/Pd have displayed excellent performance. At 800°C, and with a 65 μm thick electrolyte, the power outputs were above 1W/cm² in humidified hydrogen and 0.7 W/cm² in humidified methane. These electrodes have shown the ability to reduce CO₂ electrochemically with an efficiency that is similar to that which can be achieved for H₂O electrolysis and the anodes could operate on pure CO₂. The importance of incorporating an efficient catalyst was demonstrated. The use of 0.5 wt% of Pd is sufficient to dramatically improve the performance in such electrodes. The microstructure of impregnated LSCM-YSZ composites plays an important role in the high performance obtained. A layer of LSCM nanoparticles covering the YSZ is formed upon reduction, offering a great surface area for electrochemical reactions. The fabrication method presented in this thesis is a powerful tool for designing microstructures in situ. Among the various fuels under consideration for SOFCs, ethanol offers outstanding advantages. Half cell measurements have been performed to characterize the performance of different types of anodes when operated on ethanol/steam mixtures. Steady performance was achieved on LSCM-CGO anodes. Carbon deposits from gas phase reactions have been evidenced and were found to be responsible for the performance enhancement when the cell is operated in diluted ethanol as compared to hydrogen. At high steam content, polarization resistances of LSCM-CGO-YSZ anodes in ethanol/ steam mixtures were shown to be below 0.3 Ω.cm² at 950°C.
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Gambino, Marianna. « Structural study, computational analysis and structure-property correlations in anion conducting electrolytes for Solid Oxide Fuel Cells ». Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3882.
Texte intégralRésumé :
A combined experimental and theoretical approach has been used in order to investigate the local structural features that have an influence on ionic conductivity of IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell) electrolytes, in order to link the properties of these materials with their atomic and electronic structure.
Doped delta-Bi2O3 and LaGaO3 electrolytes for AC-SOFC applications have been studied as model compounds for oxygen-ion diffusion in fluorite-like and perovskite-like materials, due to their incredibly high anion conductivity. A combined X-Ray Absorption Spectroscopy (XAS) and Density Functional Theory (DFT) study has been carried out with the aim to unveil the role of the dopants on the short range structure of these materials, to probe the preferential association of vacancies with both dopant and regular site cations, and to highlight the preferential oxygen-ion diffusion paths. This could help to define criteria for the design of new materials with improved properties.
The influence of the electrode-electrolyte interface on the overall fuel cell ionic conductivity has been also addressed. To this aim, a novel protocol to evaluate electrode-electrolyte compatibility through Scanning X-Ray Microscopy (SXM) has been developed and cation interdiffusion has been successfully probed at the interface between some electrolyte-cathode couples.
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Fisher, James C. II. « The Reduction of CO2 Emissions Via CO2 Capture and Solid Oxide Fuel Cells ». University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1247250147.
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Naimaster, Edward J. « Effects of electrode microstructure and electrolyte parameters on intermediate temperature solid oxide fuel cell (ITSOFC) performance ». Honors in the Major Thesis, University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1298.
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