Preparation And Performance Analysis Of GDC/ESB Double Layers Electrolyte For Solid Oxide Fuel Cells

As the electrolyte of Solid Oxide Fuel Cells（SOFC）, Ga0.2Ce0.8O2-d（GDC） shows some electronic conduction at low oxygen pressure which would harmful for the open-circuit voltage（OCV） and output power of cells. And as a pour ionic conductor, Er0.6Bi1.4O3（ESB） electrolyte is unstable at reduced atmosphere which had bad influence for cells.To solve those problem, GDC/ESB double-layer electrolytes were researched at this thesis. The pour phase ESB electrolyte were systhesis by sol-gel method, and the other materials as GDC electrolyte, Ni O anode and La0.2Sr0.8Co O3-d cathode were the commercial product.The research showed that when the calcination temperature lower than 600 oC, ESB was formed but there are still some impurity phase such as Bi₂O₃. After calcined at 850 oC for 5 h, the ESB was decomposing into Bi₂O₃, Bi and Er2O3. But the pour phase of ESB was formed after calcined at 700 and 800 oC for 5 h. The XRD indicate that the compatibility of ESB between LSC and GDC is commendable, after calcined at 700 oC for 3 h, there are without impurity phase. The average Coefficient of thermal expansion（TEC） between the temperature from 25 to 700 oC is 15.91′10-6 K-1 which slightly higher than GDC at the temperature from 25 to 900 oC, and the ESB turned soft while the temperature higher than 700 oC. The conductivity of ESB at 700 oC is reached at 0.236 S cm-1.The test for the electrolyte-supported cells Ni O-GDC/YSZ/ESB-LSC, Ni O-GDC/GDC/ESB-LSC and Ni O-GDC/GDC/ESB/ESB-LSC at 700 oC showed that the Ohmic Resistance（Rohm） were 1.533, 0.731 and 0.828 W cm2, respectively; The open-circuit voltage（OCV） were 1.0536, 0.716 and 1.0416 V, respectively; And the maximum power density（Pmax） were 98.88, 170.63 and 179.98 m W cm-2, respectively. The cells with GDC as electrolyte shows better Rohm and Pmax performance than the cell with YSZ as electrolyte because of GDC have a better ionic conduction at intermediate temperature. The OCV and Pmax of GDC supported cell improved by the fabrication of ESB bi-layer.Calcined at 1400 oC for 5h, the GDC electrolyte layer of Ni O-GDC/GDC half-cell showed dense surface. The research for the anode-supported cells Ni O-GDC/GDC/ESB-LSC and Ni O-GDC/GDC/ESB/ESB-LSC showed that the resistance were lower than the electrolyte-supported cells. When measured at 700 oC, Rohm of the cells Ni O-GDC/GDC/ESB-LSC and Ni O-GDC/GDC/ESB/ ESB-LSC were 0.190 and 0.256 W cm2, the OCV were 0.705 and 1.025 V, the Pmax were 211.28 and 350.26 m W cm-2. The Rohm increased with the fabrication of ESB bi-layer, however, the OCV and Pmax improved much better. The OCV matched the YSZ supported cells, which shows that the ESB bi-layer blocked the electronic conduction.Compared the performance of single cells supported by eslctrolyte and anode, the Rohm and Pmax performance of anode-supported cells better than the electrolyte-supported cells because the anode-supported cells decreased the thickness of electrolyte, reduced the Rohm, and improved the Pmax.