88,863 research outputs found

    Protonics of perovskite electrocatalysts for energy conversion and storage systems

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    Department of Energy EngineeringWith the exponential growth in energy consumption and with finite fossil fuel resources, environmentally-friendly and sustainable energy conversion and storage (ECS) devices have received great attention from the industrial and academic communities. Ceramic electrochemical cells such as solid oxide fuel cells(SOFCs) and solid oxide electrolysis cells (SOECs), are considered as promising ECS applications because of their high-energy conversion efficiency and low pollutant emission. Solid oxide fuel cells are high-efficiency energy generation devices that convert chemical energy directly into electricity. As a reverse reaction of the fuel cell reaction, the SOEC is a device capable of producing hydrogen without any pollutants by water electrolysis. Despite these advantages, there are many problems due to the high activation energy of oxygen ion transfer, which requires a very high operating temperature. (e.g., degradation of performance, costly insulation, harsh thermos-cycle environment, slow start-up) In recent years, protonic ceramic fuel cells (PCFC) using a proton conducting oxide (PCO) as an electrolyte, have been attracting attention to solve the drawbacks of high-temperature operation because the PCOs have shown high ionic conductivity and low activation energy of the H+ transport compared with the O2- transport. To operate the PCFC efficiently, the PCFC cathode materials should have the property of electrochemical activity not only for O2- and e??? but also for H+ (so-called triple conducting oxide, TCO). However, due to the difficulties of its characterization, the proton properties of the TCOs are not fully understood yet. In this regard, the characterization of protonics in the TCO is important to understanding applications based on proton conducting oxides. This paper mainly focuses on the understanding and development of perovskite catalysts for ceramic electrochemical cells. In particular, to solve the problems mentioned above, I have comprehensively investigated the thermodynamic and kinetic properties of the oxygen ion, electron, and proton in the perovskite materials. I started with basic principles and theory of overall PCFCs and solid oxide ceramic cell in chapter 1, and then my research papers studying solid oxide fuel cell cathode material and protonic ceramic fuel cell for intermediate to low temperature ceramic fuel cells are presented as follows, 1. Effect of Fe Doping on Layered GdBa0.5Sr0.5Co2O5+?? Perovskite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells 2. Chemically Stable Perovskites as Cathode Materials for Solid Oxide Fuel Cells: La-Doped Ba0.5Sr0.5Co0.8Fe0.2O3-?? 3. Triple-Conducting Layered Perovskites as Cathode Materials for Proton-Conducting Solid Oxide Fuel Cells 4. Hybrid-solid oxide electrolysis cell: A new strategy for efficient hydrogen production 5. The First Observation of Proton Trace in Triple Conducting Oxides: Thermodynamics and Kinetics of Protonope

    Layered perovskites as electrocatalysts for energy conversion and storage systems

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    Department of Energy EngineeringWith growing concerns over energy and environmental issues, sustainable and environmentally-friendly energy conversion and storage devices have received significant attention from both the academic and industrial communities. Solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), which are collectively referred to as solid oxide cells (SOCs), are attractive energy conversion and storage systems with high energy conversion efficiency and environmental benefits. SOFCs, which directly convert chemical energy (such as H2, CH4, C3H8, etc) into electricity, represent an efficient alternative combustion system for the production of electricity. Similarly, SOECs, which convert water to hydrogen, are a clean and efficient hydrogen production system. Ideally, SOFCs and SOECs should meet several criteria, such as high performance, long term stability, and relatively inexpensive cost. However, the operation of SOFCs and SOECs still accompanies several problems, especially in relation to the electrode materials. Conventional electrode materials suffer from insufficient performance, performance degradation, redox instability, coarsening, electrode delamination, and the formation of a secondary phase. In this regard, the development of electrode materials with both high conductivity and high and stable electrocatalytic activity is a vital step for the commercialization of SOFCs and SOECs. This dissertation focuses on layered perovskite based electrode materials for SOFCs and SOECs with an aim to overcome the problems noted above. These materials show outstanding performance and stability with fast electrochemical reaction kinetics. I first discuss basic principles and present a theoretical overview of solid oxide fuel cells and solid oxide electrolysis cells in chapter 1 and then describe the experimental techniques for the fabrication and characterization of electrode materials for SOFCs and SOECs in chapter 2. Finally, my research papers on the properties of electrode materials for SOFCs and SOECs are presented as outlined below, 1. Thermodynamic and electrical properties of Ba0.5Sr0.5Co0.8Fe0.2O3-?? and La0.6Sr0.4Co0.2Fe0.8O3-?? for intermediate-temperature solid oxide fuel cells. 2. Optimization of Sr content in layered SmBa1-xSrxCo2O5+?? perovskite cathodes for intermediate-temperature solid oxide fuel cells. 3. High redox and performance stability of layered SmBa0.5Sr0.5Co1.5Cu0.5O5+?? perovskite cathodes for intermediate-temperature solid oxide fuel cells. 4. Electrochemical properties of B-site Ni-doped layered perovskite cathodes for IT-SOFCs. 5. Correlation between fast oxygen kinetics and enhanced performance in Fe doped layered perovskite cathode for solid oxide fuel cells. 6. Achieving high efficiency and eliminating degradation in solid oxide electrochemical cells by using high oxygen capacity perovskite. 7. Novel hydrogen production system: Dual Solid Oxide Electrolyzer.ope

    Mathematical modeling of solid oxide fuel cells

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    Development of predictive techniques, with regard to cell behavior, under various operating conditions is needed to improve cell performance, increase energy density, reduce manufacturing cost, and to broaden utilization of various fuels. Such technology would be especially beneficial for the solid oxide fuel cells (SOFC) at it early demonstration stage. The development of computer models to calculate the temperature, CD, reactant distributions in the tubular and monolithic SOFCs. Results indicate that problems of nonuniform heat generation and fuel gas depletion in the tubular cell module, and of size limitions in the monolithic (MOD 0) design may be encountered during FC operation

    Structural and Electrical Properties of Pulsed Laser Deposited Yttrium Doped Zirconium Oxide Thin Film Stabilization

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    Solid Oxide Fuel Cells are devices that use a series of electrochemical reactions to convert chemical energy from fuel into electricity. These fuels, such as Hydrogen (H2), Carbon Monoxide (CO), and Oxygen (O2), have a high conversion efficiency. Solid Oxide Fuel Cells, in comparison to coal power plants, produce a higher electrical conversion efficiency. Solid Oxide Fuel Cells are a possible candidate for energy production. However, Solid Oxide Fuel Cell’s high temperatures (800-1000 degrees Celsius) create a lower ionic conductivity of the electrolytes. This ionic conductivity limits Solid Oxide Fuel Cell applications. When decreasing the temperatures, the ohmic resistance, as a thin film, increases. In our research an Yttria Stabilized Zirconia layer is produced from the fine dimple grain structure allowing high flow of oxygen mobility. This ion mobility increases the ionic conductivity and decreases the ohmic losses. The goal of our research is to determine the Yttria Stabilized Zirconia thin film synthesis conditions which lead to minimum ohmic resistance in these films. The method that we will use is to test different molecular ratios of Yttrium (III) Oxide (Y2O3) and Zirconium (IV) Oxide (ZrO2) and deposit these different ratios onto the substrates. We will also use different substrates and monitor the effect each substrate on the Yttria Stabilized Zirconia thin film properties. These thin films will be characterized through electrical measurements such as Four Point Probe Resistivity measurements as well as structural and compositional characterization through Atomic Force Microscopy, Scanning Electron Microscope, and Energy Dispersive X-Ray Spectroscopy

    Fuel flexibility of solid oxide fuel cells

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    One of the major advantages of SOFCs is their high fuel flexibility. Next to natural gas and hydrogen, which are today\u27s most common fuels for SOFC-systems and cell-/stack-testing respectively, various other fuels are applicable as well. In the literature, a number of promising results show that available fuels as propane, butane, ammonia, gasoline, diesel etc. can be applied. Here, the performance of an anode supported cell operated in specialized single cell test benches with different gaseous and liquid fuels and reformates thereof is presented. Fuels as ammonia, dissolved urea (AddBlue(TM)), methane/steam and ethanol/water mixtures can directly be fed to the cell, whereas propane and diesel require external reforming. It is shown that in case of a stable fuel supply the cell performance with such fuels is similar to that of appropriate mixtures of H-2, N-2, CO, CO2, and steam, if the impact of endothermic reforming or decomposition reactions is considered. Even though a stable fuel cell operation with such fuels is possible in a single cell test bench, it should be pointed out that an appropriate fuel processing will be mandatory on the system level

    Performance of an Anode Supported Solid Oxide Fuel Cell with Indirect Internal Reforming

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    The conversion of fuel into hydrogen-rich gas is necessary for fuel cells. This can be achieved either indirectly in fuel processing systems, in which the hydrocarbon feed is converted in an external catalytic steam reformer, or directly in the fuel cell. In this paper, the unit module of solid oxide fuel cell was assembled by one reformer and four cells. The reformer was fabricated by extruded dummy cell and combined with two cells on each side respectively. The reforming catalyst was coated on internal channel of the dummy cell. The unit module has successfully tested with wet CH4 as fuel and air as oxidant and its maximum power density exceeded 150mW/cm(2) at 750 degrees C.open110Nsciescopu

    A Two-Dimensional Model of a Single-Chamber SOFC with Hydrocarbon Fuels

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    The single chamber fuel cell (SCFC) is a novel simplification of the conventional solid oxide fuel cell (SOFC) into which a premixed fuel/air mixture is introduced. It relies on the selectivity of the anode and cathode catalysts to generate a chemical potential gradient across the cell. For SCFC running on hydrocarbon fuels, the anode catalyst promotes in-situ internal reforming of the hydrocarbon and electrochemical oxidation of the syngas, while the cathode catalyst reduces oxygen simultaneously. Laboratory tests of small designs of such fuel cells have demonstrated excellent electrical performance (1, 2)
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