||Assessing the stability of scandia dopped Ni/YSZ cermet microstructures under electrolysis conditions
||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)
||Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
||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.
||Danmarks Tekniske Universitet, Risø Nationallaboratoriet for Bæredygtig Energi : Roskilde
||Brændselsceller og brint; Fuel Cells and Hydrogen; Elektrolyse; Electrolysis
Creation date: 2011-01-04
Update date: 2011-01-04