Date

2021-6

Author

Kılıç, Fahrettin

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This thesis focuses on the synthesis, characterization, and processing of LSF based composite cathode for solid oxide fuel cells. The cathode comprises three oxides; LSM, LSF and ScSZ which are synthesized by co-sputtering using combinatorial approach. The electrolyte was Scandia doped Zirconia(ScSZ), as it has attractive ionic conductivity at lower temperatures. Having chosen the electrolyte ScSZ as electrolyte. After detailed analysis with regard to conductivity and thermal expansion for each oxide, the compositions selected were La0.8Sr0.2FeO3-δ , La0.5Sr0.5MnO3-δ and Sc0.15Zr0.85O2-δ LSF, LSM, ScSZ respectively. Electrolyte powder was fabricated by Pechini method using nitrates as precursors, calcined at 900 0C. Electrolyte disc of typically 2mm thick were obtained by pressing vi and sintering at 1500 0C. This has yielded an electrolyte with ionic conductivity of 3.5x10-4 S.cm-1 at 600 0C. A total of 21 composite cathodes were deposited on electrolytes, each with a different composition. The performance of cathodes was characterized via EIS measurements on symmetric cells. A temperature ranges from 600 0C up to 800 0C was covered at 50 0C interval. LSM-LSF-ScSZ ternary diagram was mapped in terms of area specific resistance (ASR). The ASR values at 600 0C varied from 29 to 676 ohm.cm2. At 800 0C the values were significantly better which ranged from 0.33 to 5.55 ohm.cm2. The mapping of ASR values yielded a region close to LSM0.750LSF0.125ScSZ0.125 where ASR was minimum. The value obtained was 0.33 ohm.cm2 implying that the cathode is suitable for use at temperatures slightly above 800 0C. It was anticipated that in order to reduce operating temperature of SOFC to lower temperature LSM may be replaced by ruddlesden-popper type oxide. It was proposed that LaSr3Fe3O10 (rp-LSF) may be used in place of LSM with a potential to achieve this reduction.

Subject Keywords

SOFC cathodes, Combinatorial deposition, Magnetron sputtering, Electrochemical impedance spectroscopy, Symmetric cell

URI

https://hdl.handle.net/11511/91342

Collections

Graduate School of Natural and Applied Sciences, Thesis