As a chemical to electricity energy conversion technology, solid oxide fuel cells (SOFCs) must be operated at relatively high temperatures due to the high resistance of their electrodes. The low specific surface area caused by high sintering temperature during electrode fabrication, along with the poor catalytic ability of electrode materials, were the reason for the poor SOFC electrode performance. With the development of highly active electrode materials and new electrode synthesis methods like precursor solution infiltration, nano-sized, highly catalytically active materials like La0.6Sr0.4Co0.8Fe0.2O3- (LSCF), Sm0.5Sr0.5CoO3- (SSC) and Gd0.1Ce0.9O2 (GDC) have all been successfully fabricated at relatively low temperatures. A new “nano-composite” structure for SOFC electrodes, where nano-sized electrode catalysts are added into micron-sized ionic conducting (IC) materials using precursor solution infiltration, has greatly improved the electrode performance and reduced the operating temperature for SOFCs due to the large number of active reaction sites for nano-sized electrode catalysts and the fast oxygen ion transport pathway provided by the sintered IC substrates.Despite the improved electrode performance, lower operating temperatures are still desired so that cheaper materials for SOFC sealants and interconnects can be used, which will bring down the overall SOFC electricity generation cost. Moreover, long-term stability for these nano-composite electrodes is still a problem. Even at reduced operating temperatures, particle coarsening and surface cation segregation were still reported for common SOFC electrodes, compromising their electrochemical performance over time.For the work in this thesis, it is hypothesized that surface decoration methods can alter the electrochemical performance and long-term stability of SOFC nano-composite cathodes (NCCs) by changing their surface chemistry and structure. Electrochemical Impedance Spectroscopy analysis, as well as surface and composition characterization methods such as Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy analysis were conducted to test this hypothesis. Surface decoration methods like atomic layer deposition (ALD) and GDC pre-infiltration were conducted on LSCF-GDC NCCs. 1-5 nm ZrO2 ALD overcoats reduced the degradation rate of LSCF-GDC NCCs without significantly altering their initial polarization resistance (RP), while GDC pre-infiltration reduced both the RP and the degradation rate for LSCF-GDC NCCs. In both cases the decrease in SrCO3 concentration was observed after aging, which cleaned up the LSCF surface and resulted in better stability. GDC pre-infiltration was also performed on SSC-GDC NCCs. With little SrCO3 impurity phase formed during precursor solution firing, no RP or durability enhancement effect was observed. Moreover, ALD and GDC pre-infiltration were performed together for LSCF-GDC NCCs. Higher degradation rates were observed compared with uncoated cells and the reason was believed to be the reaction between ZrO2 overcoats and nano-sized GDC particles during aging, which compromised their “SrCO3 reduction” capability. Finally, precursor solution infiltration was used to fabricate SOFC anodes and symmetric anode tests showed lower anode RP for the infiltrated anodes compared with commercial ones. Ni infiltration was also conducted on commercial Ni- (Y2O3)0.08(ZrO2)0.92 (YSZ) anodes and peak power density of the anode infiltration commercial SOFCs was significantly increased compared with un-infiltrated ones.
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