Fabrication And Investigation Of Anode-supported Intermediate Temperature Solid Oxide Fuel Cells With Novel Composite Electrolytes

Recent years, much effort is directed to novel thin electrolytes, such asLaGaO_3- and ceria-based electrolytes, for intermediate temperature solid oxidefuel cells (IT-SOFCs). In this thesis, anode-supported IT-SOFCs with thincomposite electrolyte films of LaGaO_3- and ceria-based electrolytes werefabricated and investigated.The chemical compatibility between the ceria based electrolytes and theLa_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) electrolyte were investigated, and found thatLa_0.45Ce_0.55O_1.775 (LDC) is of much better chemical compatibility with LSGMthan the other ceria-based electrolytes. Anode-supported SOFCs withLDC-LSGM bilayer electrolyte were fabricated, in which the LDC layer canrestrain the reaction of LSGM and NiO at high temperatures and the LSGM layercan block the electronic conductivity of the LDC electrolyte. Using pure LSC asthe cathode, the open-circuit voltages (OCV) of the single cells are independent ofthe thickness of LDC layer. However, due to the Co diffusion from the LSCcathode to the LSGM electrolyte, the OCV relies on the thickness of the LSGMlayer, and reaches above 1.0 V with a LSGM layer over 50um. The conductivityof LDC in single cell is 0.117 S/cm under operation at 800℃. The conductivity ofLSGM depends on the thickness of the LSGM layer, which is about 1.9 S/cm withthe thickness of LSGM layer below 50 μmand about 0.22 S/cm with the thicknessof LSGM layer over 100 μm. It is found that the open-circuit potential of anodesupported bilayer electrolyte single cell with Sm0.5Sr0.5CoO3 (SSC) cathode isstable for 112 h at 1.045 V. The electrochemical properties of the composite cathodes of LSC and LDCwere investigated. The presence of LDC in LSC-LDC composite cathodesuppresses the growth of LSC particles, and results in a fine electrodemicrostructure. The AC impedance spectra indicate that the cathodic interfacialresistance is effectively reduced in the composite cathode. In addition, the ohmicresistance of the single cells decreases with the increase of the LDC content,indicating that LDC also suppresses the Co diffusion from the LSC cathode to theLSGM electrolyte. The optimum content of LDC in the LSC-LDC compositecathode is around 50 wt.%. Pure methanol or mixtures of methanol and water were investigated as fuelsfor anode-supported bilayer electrolyte SOFCs with Ni-Gd0.1Ce0.9O1.95 (GDC)anode at 700oC. It is found that pure methanol or low diluted methanol fuelsresults in coking on anode. The product distribution in the tail gas from the anodechamber demonstrates that carbon deposition can be suppressed under celloperation at high current density.