OPTIMIZATION OF MICROSTRUCTURE AND COMPOSITION AND THE EFFECTS OF ATOMIC LAYER DEPOSITION SURFACE TREATMENT ON LSCF-BASED CATHODES FOR INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS
- Author(s): Johnson, Sean
- Advisor(s): Lee, Min Hwan
- et al.
This study focuses on the development of (La(0.6)Sr(0.4))(0.95)Co(0.2)Fe(0.8)O(3-d) LSCF-based cathodes for solid oxide fuel cells, with the purpose of lowering operating temperature and improving cell performance for commercialization. The first part of the study investigated the effects of using Co3O4 as a sintering aid, which was shown to enhance grain growth and interconnectivity and to dramatically lower cell impedance for both LSCF and LSCF- Gd(0.1)Ce(0.9)O(2-d) (gadolinia-doped ceria; GDC) composite cathodes. Co3O4 concentration was optimized for both the functional layer and the current collecting layer of the cathode. The second portion of the study explores the relationship between electrode layer thickness and cell impedance. It was shown that increasing functional layer thickness beyond a limiting value increases cell impedance, and that both ohmic resistance and polarization resistance asymptotically decrease with increasing thickness of the current collecting layer. Optimal thicknesses were found for each of the electrode layers. Finally, ultra-thin layers of yttria-doped ceria were deposited via atomic layer deposition (ALD) onto the functional layer of bilayer LSCF-GDC/LSCF cathodes as well as pure LSCF cathodes. It was shown that for both sets of cells, ohmic resistance initially increased with YDC deposition, but that subsequent increases in YDC thickness had an inverse relationship with ohmic resistance. This behavior has been observed in previous studies, and prolonged heat treatment will be needed to fully realize the benefits of the functionalization. Polarization resistance was negatively affected by YDC functionalization for both sets of cells due to a blocking of oxygen reaction sites on the surface of the LSCF electrode. In summary, Co3O4 concentration and electrode layer thickness were optimized to maximize performance for LSCF-based cathodes, and ALD functionalization was investigated as a method for further improving cathode performance.