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Due to their high energy conversion efficiencies and low emissions, Solid Oxide Fuel Cells (SOFCs) show promise as a replacement for combustion-based electrical generators at all sizes. Further increase of SOFC efficiency can be achieved by microstructural optimization of the oxygen-ion conducting electrolyte and the mixed ionic-electronic conducting cathode. By application of nanoscaled thin films, the exceptionally high efficiency allows the realization of mobile SOFCs.
This work deals with microstructural characterisation, modelling and simulation of SOFC electrodes with the goal of optimizing the electrode microstructures. Methods for a detailed electrode analysis based on focused ion beam (FIB) tomography are presented. A 3D FEM model able to perform simulations of LSCF cathodes based on 3D tomography data is shown. A model generating realistic, yet synthetic microstructures is presented that enables the optimization of microstructural characteristics.
Hydrogen Technology: Fundamentals and Applications relates theoretical concepts to practical case studies in the field of hydrogen technology with an emphasis on materials and their applications. To implement hydrogen conversion production processes, it is crucial to understand the structural, microstructural, textural, thermal, catalytic, and electrochemical properties of materials. Covering nanomaterials, heterogeneous catalysis, greenhouse gas conversion, reforming reactions for hydrogen production, valorization of hydrogen energy, biomass valorization, the hydrogen economy, and its technical feasibility, this book addresses how bio/hydrogen technology can be used to solve environmental problems, including how to produce, convert, and store energy through electro/catalytic reactions and chemical valorization. Providing an understanding of the different factors involved, such as the availability of raw material, location, viable process and production scale, and economic criteria, this book will especially be of interest to engineers, scientists, and students in the field of hydrogen technology. - Explains the phenomena that govern electrocatalytic/catalytic reactions - Covers the study of new materials design and industrial processes - Includes process improvements for obtaining hydrogen via chemical and biological processes
This thesis introduces (i) amendments to basic electrochemical measurement techniques in the time and frequency domain suitable for electrochemical energy conversion systems like fuel cells and batteries, which enable shorter measurement times and improved precision in both measurement and parameter identification, and (ii) a modeling approach that is able to simulate a technically relevant system just by information gained through static and impedance measurements of laboratory size cells.
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 this work, a deeper understanding of the electrochemical oxidation at SOFC anodes was gained by the experimental characterization of patterned Ni anodes in H2-H2O and CO-CO2 atmosphere. By high resolution data analysis, the Line Specific Resistance attributed to charge transfer and its dependencies on gas composition, temperature and polarization voltage were identified. Furthermore, the comparison of the performance of patterned and cermet anodes was enabled using a transmission line model.
A high resolution electrochemical impedance spectroscopy study on anode supported single cells (ASC) is presented. The cells were characterised over a broad range of operating conditions, including different temperatures, current densities and various cathode and anode gas compositions.The analysis of the distribution of relaxation times combined with the numeric accuracy of a CNLS fit enabled the identification of five different processes contributing to the total polarisation loss of an ASC.
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.
In this book, a new procedure to analyze lithium-ion cells is introduced. The cells are disassembled to analyze their components in experimental cell housings. Then, Electrochemical Impedance Spectroscopy, time domain measurements and the Distribution function of Relaxation Times are applied to obtain a deep understanding of the relevant loss processes. This procedure yields a notable surplus of information about the electrode contributions to the overall internal resistance of the cell.
Mixed ionic-electronic conducting (MIEC) ceramics as oxygen transport membranes (OTMs) can provide high oxygen permeation rates at comparably low energy demands. For this purpose, Ba?.?Sr?.?Co?.?Fe?.?O??? (BSCF) shows the best performance under ideal operating conditions. Thermal and chemical stability investigations, electrical behavior ?(T,pO?,t), and oxygen exchange parameter extraction by means of electrical conductivity relaxation resulted in a far better understanding of the BSCF system.