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| Book/Report/Dissertation / PhD Thesis | PUBDB-2017-01522 |
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2017
Verlag Deutsches Elektronen-Synchrotron
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2017-01522
Report No.: DESY-THESIS-2017-011
Abstract: A detailed study of three solid oxide fuel cells (SOFCs) related model systems is presented in this work with the aim of the better understanding of the structural changes in cell components associated with their operation. The first model system is an La$_{0.6}$Sr$_{0.4}$CoO$_{3−δ}$ (LSC) on yttria-stabilized zirconia (YSZ). Changes in the YSZ(100) single crystal surface structure buried under the squared LSC microelectrode were studied at a synchrotron under operational conditions. High flux photon beam at the synchrotron allowed access to the LSC/YSZ interface. Structural information from the substrate surface at an atomic scale was acquired. Element-specific anomalous XRD data allowed to distinguish between Y and Zr scattering contributions. For the first time, it was shown that the Y cation concentration at the electrode/elec- trolyte interface strongly depends on the sample environment and the applied potential. The second model system is a Pt/YSZ. Buried YSZ(111) surface and dense Pt film morphology changes under operational conditions were addressed. High-energy X-rays were necessary to collect surface-sensitive information from the interface due to highly absorbing Pt film. The main conclusion is - under conditions applied, the YSZ single crystal surface remains stable at an atomic level. A nagging topic of the Pt "phase oxide" formation at the Pt/YSZ interface during anodic polarization was also raised. Although XRD data did not show a clear evidence of PtO x presence at the interface, energy- dispersive X-ray analysis of the film cross-cut profile after the synchrotron experiment revealed distinct oxygen signal from delaminated parts of the film. Last but not least, the structure of a ZrO$_2$ ultrathin film grown on a Pt$_3$ Zr(0001) single crystal was studied in ultra-high vacuum for the first time be means of SXRD. This model system is aiming to improve understanding of the electrolyte materials based on ZrO$_2$ (e.g. YSZ) at an atomic level. The results obtained, can be summarized as follows: the oxide film is not stable at the oxygen pressure higher than 10$^{−6}$mbar; the density-functional theory models tend to overestimate the film-substrate distance; there is more than 1ML of a reconstructed Pt present in the top-most layer of the Pt$_3$Zr(0001) beneath the zirconia film.
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