| Solid oxide fuel cells are being considered as an efficient, clean, economic, and friendly candidate power generation technology to replace conventional thermal engines for power generation at high efficiencies (40～50%). Facing the worldwide energy crisis, SOFCs have received extensive research attentions. Carbon deposition and sulfur poisoning on the anode have limited the broader application of SOFC, when in use of the readily available low-cost hydrocarbon fuel. CeO2-based anode materials as alternatives to the traditional Ni-zirconia cermet, known to have exellent performance when using H2 fuels but most likely unsuitable for direct use of hydrocarbon fuels due to the inherent carbon deposition, have the abilities of resistance to carbon deposition and sulfur poisoning. In this paper, the novel ceria based anode materials co-doped by the rare earth elements Y and Yb were investigated in order to obtain high cabon resistance and sulfur tolerance with higher electrical conductivity as well as more active oxygen in lattice. Therefore, we investigated in detail and obtained Ni-based double rare earth elements doped CeO2 materials with good performance of carbon deposition resistance and sulfur poisoning.First of all, the novel materials with Ce0.8YxYb0.2-xO<sub>2-δ formulation were prepared by glycine combustion method and coprecipitation process, respectively. By virtue of the investigation on the phase structure, electrical conductivities and thermal properties and comparing the compatibility with electrolyte GDC, the material with Ce0.8Y0.1Yb0.1O2-δ formulation was regarded as the novel anode material with potential ability of avoiding carbon coking and sulfur poisoning. In the whole thesis, this material was studied as the main researching target in order to identify the role of the doping with double rare earth elements.Secondly, in order to study the catalytic performance and the long term stability, both electrolyte-supported and anode-supported type cells with the novel Ni-Ce0.8Y0.1Yb0.1O2-δ anode was prepared. The performance of Ni-Ce0.8Y0.1Yb0.1O2-δ anode was tested in H2 and CH4 at elevated temperatures, respectively. In contrast, the single rare earth element Y, Yb and Gd doped Ni-Ce0.8Y0.2O2-δ , Ni-Ce0.8Yb0.2O2-δ and Ni-Ce0.9Gd0.1O2- anodes were also tested. The results show that Ni-Ce0.8Y0.1Yb0.1O2-δ has the best performance among all the anodes under investigation. At 750℃, the maximum power densities were 247 mW·cm-2 and 163 mW·cm-2 in H2 and CH4, respectively. Specifically, in CH4, the cell can operate stably more than 80h, without visible carbon deposition. Therefore, the Y and Yb co-doped anode significantly improved the performance of carbon deposition resistance.Finally, the sulfur tolerance of the novel anode was investigated in detail. When using H2 containing H2S as the fuel, the performance of Ni-Ce0.8Y0.1Yb0.1O2-δ , Ni-Ce0.8Y0.2O2-δ , Ni-Ce0.8Yb0.2O2-δ , Ni-Ce0.9Gd0.1O2- anodes were tested for comparison. Ni-Ce0.8Y0.1Yb0.1O2-δ anode is still the best anode material among the all anodes under investigation. At 700℃, with H2S of 5 ppm and 20 ppm, the high power density degraded by 5% and 12%. There is only 0.6% degration in power output when operated at a constant current density of 110 mA/cm2 as the fuel was switched to one contaminated with 5 ppm H2S.The results showed that, Y and Yb double dopant greatly improved the ability of sulfur poison talerance of the anode, optimized the performance and stability of the anode materials in H2S. The results also demonstrated that Ni-Ce0.8YxYb0.2-xO<sub>2-δ composite anode could be promising to be considered as a potential candidate of SOFCs anode for directly utilization of hydrocarbon fuels. |
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