Modification And Performance Investigation Of Nickel Based Anode For Solid Oxide Fuel Cells

Solid oxide fuel cells （SOFCs） are the interesting topic due to the obvious merits.It is the challenge for the existing fuel cell technologies to provide a commercialpath. The system costs and fuel infrastructures are the main critical bottlenecks. Oneof the merits of the SOFCs is the good fuel flexibility. Therefore, many gases, suchas hydrocarbon, can be used as the fuels. However, the investigation of the practicalsystem has been still hampered by some problems, such as the coking on thewell-known conventional nickel-based anode once using hydrocarbon fuel such asmethane or propane that the occurance of severe degradation will compromise thecell performance. During the current time, SOFCs are being directly oriented to theportable devices, which require liquid fuel favorable for SOFC operation. Accordingto the above problems, we concentrated on the anodes which can work steadily withtolerance to sulfur and coking for a long time and the anodes which are suitable forammonia-fueled SOFC. At the same time, we studied some materials which can beused as the symmetrical electrode.The sulfur tolerance improvement of Ni-YSZ anode by alkaline earth metal oxideBaO for solid oxide fuel cells was studied: The anodic performance of Ni-Y2O3stabilized ZrO2（Ni-YSZ） modified by alkaline earth metal oxide BaO wasinvestigated for solid oxide fuel cells operating in H₂S-containing hydrogen fuels.The EDS results indicated that the amount of BaO was about5%. The cell withBaO/Ni-YSZ anode exhibited almost constant peak power densities when the fuelwas switched from wet hydrogen to50ppm H₂S contaminated wet hydrogen andgood stability in wet H₂S-contained hydrogen fuels with H₂S concentrationgradually increased from5to50ppm. The EDS and XPS results demonstrated thatno element S was detectable after sulfur poisoning testing. High water adsorptionability of BaO could be the primary reason for the high sulfur tolerance. Theobtained results confirmed the previous conclusion that BaO/Ni interfaces can resistnot only deactivation by coking but also sulfur poisoning of a conventional Ni-YSZanode.The enhanced sulfur and carbon coking tolerance of novel Co-doped Ceria basedanode for solid oxide fuel cells were concentrated: Doubly doped CeO₂based anodewith Y and Yb was considered for direct methane solid oxide fuel cells. The poweroutput of the cell with Ni-Ce_0.8Y_0.1Yb_0.1O_1.9anode and stability at varioustemperatures were investigated when air was used as oxidant and pure H₂,5ppmH₂S containing H₂and dry CH₄as fuel, respectively. At750oC, the cell displayedstable power output for120h at200mA cm-2when fueled with dry CH₄, suggesting the carbon deposit was largely absent on the anode, which was confirmed by theSEM observation and EDS results. The results also proved that the rare earthelements Y and Yb affected the sulfur tolerance performance of the anode in acooperative fashion leading to good anode stability in the contaminated fuel. TheSEM and EDS results provided evidence that the cell with Ni-Ce_0.8Y_0.1Yb_0.1O_1.9anode was tolerant toward the H₂S contamination. The remarkable performancessuggested that co-doped CeO₂anode was an attractive electrode component fordirect hydrocarbon solid oxide fuel cells and might also be used as a catalyst forreforming of hydrocarbon fuels and for removal of fuel gas contaminations such assulfur.The improved performance of ammonia-fueled solid oxide fuel cell with SSZ thinfilm electrolyte and Ni-SSZ anode functional layer was investigated: Ammoniaoffers several advantages over hydrogen as an alternative fuel. However, usingammonia as a hydrogen source for fuel cells has not been received enough attentions.In this chapter, Scandia-stabilized Zirconia （SSZ） thin film electrolyte and Ni-SSZanode functional layer were developed by tape casting in order to obtain high poweroutput performance in ammonia, the results of a SOFC running on ammonia weredescribed and its performance was compared with that when running on hydrogen.In order to improve the performance of the cell at higher temperatures, the anodewas modified by iron through infiltration. A direct comparison of the performance ofthe modified cell running on either hydrogen or ammonia showed that the cell inammonia generated slightly higher power densities at700and750oC. Theperformance in ammonia, using the anode catalyst, was comparable to that inhydrogen. The results indicated that ammonia could be treated as a promisingalternative fuel by selecting an appropriate catalyst.A novel doped CeO₂-LaFeO₃composite oxide as both the anode and cathode forsymmetrical solid oxide fuel cells was studied: A novel composite oxideCe（Mn,Fe）O2-La（Sr）Fe（Mn）O3（CFM-LSFM） was synthesized and evaluated as theelectrode material for a symmetrical solid oxide fuel cell. The symmetrical cell withCFM-LSFM electrodes was fabricated by tape-casting and screen printing technique.The power-generating performance of this cell was comparable to that of the cellwith the Ni-SSZ anode and LSM-SSZ cathode. During the120h long-term test inhydrogen at800oC, the performance increased by8.6%from256up to278mWcm-2. This was attributed to the decrease of polarization resistance and ohmicresistance during the test. The XRD results showed the presence of Fe, MnO andsome unknown second phases after heat-treating the electrode materials in H₂whichmay be beneficial to the anode process. The phenomenon of the gradual decrease of polarization resistance as the increase of current density possibly resulted from theincreasing content of water in the anode.