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Solid oxide fuel cells offer great prospects for the sustainable, clean and safe conversion of various fuels into electrical energy. In this thesis, the performance-determining loss processes for the cell operation on reformate fuels are elucidated via electrochemical impedance spectroscopy. Model-based analyses reveal the electrochemical fuel oxidation mechanism, the coupling of fuel gas transport and reforming chemistry and the impact of fuel impurities on the degradation of each loss process.
The past three decades have witnessed the great success of lithium-ion batteries, especially in the areas of 3C products, electrical vehicles, and smart grid applications. However, further optimization of the energy/power density, coulombic efficiency, cycle life, charge speed, and environmental adaptability are still needed. To address these issues, a thorough understanding of the reaction inside a battery or dynamic evolution of each component is required. Microscopy and Microanalysis for Lithium-Ion Batteries discusses advanced analytical techniques that offer the capability of resolving the structure and chemistry at an atomic resolution to further drive lithium-ion battery research and development. • Provides comprehensive techniques that probe the fundamentals of Li-ion batteries. • Covers the basic principles of the techniques involved as well as its application in battery research. • Describes details of experimental setups and procedure for successful experiments. This reference is aimed at researchers, engineers, and scientists studying lithium-ion batteries including chemical, materials, and electrical engineers, as well as chemists and physicists.
This work presents a numerical FEM framework, capable of predicting SOFC performance under technically relevant, planar stack contacting conditions. A high level of confidence in the model predictions is supplied by using exclusively experimentally determined material/kinetic parameters and by a comprehensive validation. The presented model aids SOFC stack development by pre-evaluating possible material choices and design combinations for cells/interconnectors without any experimental effort.
In dieser Arbeit wird der Stackbetrieb von Festoxidzellen (engl. Solid Oxide Cells, SOCs) mit Hilfe eines Simulationsmodells analysiert. Hierfür werden sämtliche gekoppelten physikalischen und chemischen Teilprozesse innerhalb einer zweidimensionalen Geometrie einer einzelnen Stackebene abgebildet. Nach der Parametrierung mit experimentellen Daten und einer umfangreichen Validierung, wird das Modell auf drei Fragestellungen der SOC-Technologie angewendet. - In this work, the stack operation of solid oxide cells (SOCs) is analyzed by a simulation model. For this purpose, all coupled physical and chemical sub-processes are represented within a two-dimensional geometry of a single stack level. After parameterization with experimental data and extensive validation, the model is applied to three research issues in SOC technology.
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The current work analyzes degradation effects in solid-oxide fuel cell anodes with the phase-field method. A model extension for interface diffusion is formulated and calibrated. Large-scale 3D-simulations provide interesting insights into phenomena at the microscale which are responsible for the degradation
Diese Arbeit präsentiert ein physikalisch motiviertes Modell zur Vorhersage des Strom-/Spannungsverhaltens von PEM-Brennstoffzellen. Durch umfangreiche Impedanzmessungen und DRT-Analysen wurden alle Verlustprozesse identifiziert und quantifiziert. Das entwickelte Modell wurde erfolgreich validiert und bietet Einblicke in die internen Vorgänge der Brennstoffzelle. Es ermöglicht eine gezielte Optimierung und zeigt großes Potenzial für die Leistungssteigerung von PEM-Brennstoffzellen. - This work presents a physically motivated model for predicting the current/voltage behavior of PEM fuel cells. Extensive impedance measurements and DRT analyses were used to identify and quantify all loss processes. The developed model was successfully validated and provides insights into the internal processes of the fuel cell. It enables targeted optimization and shows great potential for increasing the performance of PEM fuel cells.
Die Hochtemperatur-Brennstoffzelle (SOFC) als Strom- und Wärmeproduzent der Zukunft stellt eine wichtige Schlüsseltechnologie für eine klimafreundliche Energieversorgung dar. Vorrangige Entwicklungsziele sind die Verbesserung der Lebensdauer und die Verringerung der Kosten der SOFC-Komponenten. In dieser Arbeit werden mikrostrukturelle Veränderungen, die während der Zellherstellung und im Betrieb (Alterungsverlauf) auftreten, durch den Einsatz mehrskaliger Untersuchungsmethoden identifiziert. - The solid oxide fuel cell (SOFC) as electricity and heat producer of the future represents a key technology in the context of a climate-friendly energy supply. Research focuses on the improvement of the lifetime and cost reduction of the SOFC components. In this work, microstructural changes that occur during cell production and operation (aging process) are identified by multiscale examination methods.
Diese Arbeit präsentiert ein physikalisch motiviertes Modell, welches die Zellspannung einer Lithium-Ionen-Batterie auf Basis der Zellimpedanz vorhersagt. Das Modell wurde an einer kommerziellen Pouchzelle parametriert und validiert. In einer umfassenden Simulationsstudie wird der Einfluss der Elektrodenmikrostruktur auf die Energie- und Leistungsdichte der Zelle quantifiziert. Darüber hinaus wird eine Routine zur Entwicklung anwendungsspezifischer Zelldesigns vorgestellt. - This work presents a physically motivated model that predicts the cell voltage of a lithium-ion-battery based on its impedance. The model was parameterized and validated on a commercial pouch cell. In a comprehensive simulation study, the influence of the electrode microstructure parameters on the energy and power density is quantified. Furthermore, a routine for the development of application-specific cell designs is developed.