Solid-oxide fuel cells (SOFCs) are energy conversion devices that theoretically have the capability of producing electrical- energy for as long as the fuel and oxidant are supplied to the electrodes and perfonnance is expected for at least 40,000 hours. However, it is observed that perfonnance degrades under repeated thennal cycling conditions, which limits the practicaI.operating life of these SOFCs. Therefore, the mechanism of damage to planar and integrated planar SOFCs (IPt' SOFCs) on thennal cycling is the subject of this thesis. A detailed literature review has been carried out and a mechanical and thennal properties database of the key materials used in these SOFCs has been built up. Extensive work has been done on the residual ~tress analysis of anode-supported and inert substrate supported SOFCs. Analytical model, surface profile measurement (Talysurf) and XRD stress analysis were used to detennine t4e residual stresses in the components. From this study, it was found that the difference of thennal expansion coefficients between components in the SOFCs is the dominant source of stress during thennal cycling in the absence of significant temperature gradient. For the integrated planar SOFCs, it was found tha~ the cells degraded due to the failure of the sealing materials during cooling. For anode supported planar SOFCs, the electrolyte (YSZ) is under high compressive stress when cooling from sintering or operating temperature to room temperature and the anode is under very small tensile stress. The results from theoretical analysis, XRD stress measurement and literature were compared and found that they agreed with each other quite well.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:486561 |
| Date | January 2008 |
| Creators | Sun, Baoguo |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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