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Title Assessing the stability of scandia dopped Ni/YSZ cermet microstructures under electrolysis conditions
Author Skouloudi, Eirini
Supervisor Ramos, Tania (Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Mogensen, Mogens Bjerg (Fuel Cells and Solid State Chemistry Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2010
Abstract The present thesis focuses on understanding the impact of high steam contents on the microstructure of Ni/(Sc)YSZ & Ni/YSZ electrodes and subsequent performance degradation. Preliminary experiments performed at Risø National Laboratory, Denmark, show that different combinations of anode supports and active electrodes were impacted differently by prolonged exposure to high steam contents in the atmospheres. Assessing the reproducibility of the preliminary results, and understanding the conditions and mechanisms behind the exhibited degradation is a key for improving solid oxide cell fabrication for electrolysis purposes. The study is performed by using two different designs of symmetric cell setups and electrochemical impedance spectroscopy (EIS). The deconvolution and fitting of the obtained impedance spectra was performed using complex non-linear least squares fitting routine (CNLS). The pre and post-test microstructures were evaluated by Scanning Electron Microscopy (SEM). Selected samples were further analysed by low voltage SEM (LV-SEM), in order to determine the differences in Ni percolation. The symmetric cells have been fingerprinted at temperatures between 650 – 850 °C, under various steam contents (3 %, 17 %, 42 %, and 72 %) in H2. A degradation study was also performed at 850 °C, 72 % H2O in H2 for a prolonged time period (~110h). Type II symmetric cells, with two anode supports and Ni/ScYSZ electrodes; exhibit a stable polarisation resistance (Rp) after the degradation study which is consistent with the LV-SEM micrographs showing percolating Ni in the active electrodes. The study reveals a promising stability of Ni/ScYSZ microstructures under high steam contents. The increase seen in the series resistance (Rs) is associated with locally extensive loss of percolating Ni in the anode support. Type III symmetric cells, with single anode support, and either Ni/ScYSZ or Ni/YSZ electrodes were produced to imitate production protocols of full cells. The performance of individual components under testing conditions can provide useful information for full cell performance and degradation studies. The impact of high steam content on Type III symmetric cells is not conclusive due to lack of reproducibility between them. The reasons for this lack of reproducibility are thought to be due to electronic leaks via the electrolyte.
Imprint Danmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi : Roskilde
Pages 84
Keywords Brændselsceller og brint; Fuel Cells and Hydrogen; Elektrolyse; Electrolysis
Original PDF Eirini_Skouloudi_master_thesis.pdf (5.03 MB)
Admin Creation date: 2011-01-04    Update date: 2011-01-04    Source: dtu    ID: 272067    Original MXD