Study On Novel Anode And Cathode Material For Intermediate-temperature Solid Oxide Fuel Cell

The core materials of SOFC are electrolyte, anode and cathode. La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ(LSGM) is the promising electrolyte for IT-SOFC, however, the electrolyte is restricted to apply because of the reaction with Ni cermet. Ce_1-xTm_xO(2-δ)(Tm= Mn, Co, Fe, Cu, Ni) have been investigated in order to searching the novel anode, which could be suited with the LSGM electrolyte. We also research the electrochemical behavior of Ce_1-xFe_xO_2-δ as a possible SOFC anode materials for the direct oxidation of methane. At same time, a novel cathode material have been investigated. At last, a single solid oxide fuel cell is prepared with the novel anode and cathode running on hydrogen or methane in this thesis.The solid solubility limit, crystal structure, thermal expansion rate, and electrochemical performance of Ce_1-xTm_xO(2-δ)(Tm= Mn, Co, Fe, Cu, Ni) have been investigated. Ce_1-xTm_xO(2-δ) have been synthesized by the citrate method. The solid solubility limit of the Ce_1-xTm_xO(2-δ) is about 0.1⁰.2. The solid solution has a cubic symmetry. The electrochemical behavior of anode has been analyzed by electrochemical impedance spectroscopy. Ce_1-xTm_xO(2-δ) have a significant effect on the electrochemical oxidation of hydrogen at these temperatures(550⁷00℃), the polarization resistance decreases with increasing doping element content while the lower polarization resistances appear in humidified H2 than in dry H2. The polarization resistances of Ce_0.9Fe_0.1O_2-δand Ce0.8Fe0.2O2-δrespectively show 0.975 ?cm2 and 0.577?cm2 in humidified H2 at 700℃. Therefore, Ce_1-xFe_xO_2-δ (x=0.1, 0.2) will be a promising candidate for IT-SOFC anode material. Second, the catalytic activity for direct oxidation of dry methane and long-term performance stability of Ce_1-xFe_xO_2-δ (FDC, x=0.1, 0.2) have been investigated. Ce_1-xFe_xO_2-δ (x=0.1, 0.2) has shown the properties of rapid direct electrochemical oxidation of methane at these temperatures(550⁷00℃), the polarization resistance decreases with increasing Fe content. The polarization resistances of Ce_0.9Fe_0.1O_2-δand Ce0.8Fe0.2O2-δrespectively show 2.25Ωcm² and 1.27Ωcm² in humidified CH4 at 700℃.Therefore, Ce_1-xFe_xO_2-δ (x=0.1, 0.2) will be a promising candidate for IT-SOFC anode material to direct oxidate dry methane.The crystal structure, thermal expansion rate, electrical conductivity and electrochemical performance of Sm0.5Sr0.5MxCo1-xO3 -δ(M=Fe, Mn) have been investigated. Two crystal structures have been observed in the specimens of Sm0.5Sr0.5FexCo1-xO3-δ(SSFC) at room temperature, the perovskite structure of SSFC has an Orthorhombic symmetry for 0≤x≤0.4 and a cubic symmetry for 0.5≤x≤0.9. The specimens of Sm0.5Sr0.5MnxCo1-xO3-δ(SSMC) crystallize in an Orthorhombic structure. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of SSC, can be achieved to lower TEC values with more Fe and Mn substitution. Especially, Sm0.5Sr0.5Mn0.8Co0.2O3-δexhibits good thermal compatibility with La0.8Sr0.2Ga0.8Mg0.2O3. The polarization resistance increases with increasing Mn content, Nevertheless, the polarization resistance of SSFC increases with increasing Fe content, but when the amount of Fe reaches to 0.4, the maximum is obtained while the resistance will decrease when the amount of Fe reaches above 0.4. Sm0.5Sr0.5Fe0.8Co0.2O3-δelectrode exhibits high catalytic activity for oxygen reduction operating at temperature from 700 to 800℃.A single solid oxide fuel cell is prepared with the novel anode (Ce0.8Fe0.2O2-δ) and cathode (Sm0.5Sr0.5Fe0.8Co0.2O3-δ) running on hydrogen or methane. The maximal power density is 98mw/cm2 running on humidity hydrogen at 800℃. The maximal power density is 52.2mw/cm2 running on humidity methane at 800℃. Moreover, very little carbon is detected on the anode, suggesting that carbon deposition was limited during cell operating.