This study investigated the overpotential performance enhancement of cathodes in low temperature solid oxide fuel cells (LT-SOFCs) due to the addition of carbonates to traditional Ce0.9Gd0.1O2 solid oxide fuel cell (SOFC) electrolytes. It was postulated in this study that this enhancement was due to the protonic conductivity of the carbonates. This provided an electrolyte with a dual conduction mechanism which improves the catalytic performance of the cathode.
The cathode systems investigated were characterised for overpotential loss, conductivity and thermal expansion matching with the electrolyte. This produced results which predicted power outputs for a standard SOFC configuration as high as 970, 524 and 357 mW/cm2 at operational temperatures of 650oC, 600oC and 550oC. The benefits of these high power outputs and their potential to further reduce SOFC operational temperature was discussed.
This study developed a cost-effective, reliable and commercially scalable manufacturing process for carbonate/Ce0.9Gd0.1O2 electrolytes. This pressureless sintering method is the first reported in literature, and is a promising replacement for the current hot-pressing technique currently used for these electrolytes.
The electrolyte composition examined was 70 wt% Ce0.9Gd0.1O2 with 30 wt% carbonates (67 mol% Li2CO3 / 33 mol% Na2CO3). The cathode examined in this study was a composite cathode consisting of 50-90 wt% functional cathode material (Gd1-xSrxCoO3 with 10 to 30 mol% Sr doping on the Gd site) with a balance of electrolyte. It was determined that the composite cathode system with 10 wt% electrolyte and 20-30 mol% Sr doping was the optimal composition when operating at 600oC and above, with predicted power densities of 524 and 510 mW/cm2 at 600oC. At operational temperatures between 550oC and 600oC (and potentially lower), it was determined that a composite cathode system with 30 wt% electrolyte and 10-30 mol% Sr doping was the optimal composition.
It was found that the presence of carbonates in the electrolyte decreased the overpotential losses of the cathode by 50-70% at 600oC for system studied; indicating that an improvement in cathodic performance coupled with the high conductivities of the electrolyte is most likely responsible for the high power outputs seen in literature. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-04-25 15:53:37.928
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OKQ.1974/1821 |
| Date | 27 April 2009 |
| Creators | Kilius, Linas |
| Contributors | Queen's University (Kingston, Ont.). Theses (Queen's University (Kingston, Ont.)) |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | 7613663 bytes, application/pdf |
| Rights | This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner. |
| Relation | Canadian theses |
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