Preparation And Characterized Research Of The Novel Composite Cathode Materials For SOFCs

Solid oxide fuel cell（SOFC） is a power generation device, which can convert the chemical energy of fuels into electrical energy by electrochemical redox reaction. To improve the working efficiency of SOFC, in addition to developing electrolyte materials with high ionic conductivity to reduce the ohmic resistance, searching for new cathode with superior performance under the operating temperature is also an important direction of research. Spinel oxides Mn_1.5Co_1.5O₄（MCO） has been extensively studied as protective layer of SOFCs interconnect because of its high electronic conductivity and excellent structural stability. In this paper, the MCO was modified by oxygen ion-conductor Ce_0.8Sm_0.2O_1.9（SDC） to get a mixed ionic-electronic conductor, then the feasibility of this mixture as cathode of SOFCs was explored.In this work, nanoporous composite cathodes Mn_1.5Co_1.5O₄-Ce_0.8Sm_0.2O_1.9（MCO-SDC） was prepared separately by traditional mechanical mixing method and novel one-pothydrothermal synthesis technology. The results from XRD analysis test show that Mn_1.5Co_1.5O₄（MCO） and Ce_0.8Sm_0.2O_1.9（SDC） which have been prepared by EDTA-citric complexing method are single phase. Another, composite powders MCO-SDC prepared by one-pot hydrothermal synthesis method is a mixture phase of spinel and fluorite. Furthermore, good compatibility between the MCO materials and YSZ、SDC electrolyte are also tested.The anode-supported single cells have been fabricated with different composite powders MCO-SDC（50:50wt% 、 60:40wt% 、70:30wt%） as cathode and YSZ as electrolyte. From its performance of discharge and impedance spectroscopy we can observe that MCO-SDC50（50:50wt%） cathode has the best electrochemical performance with low polarization resistance. The maximum power density of single cell MCO-SDC50 with mechanical mixing method is 914.77 m W·cm^-2、656.5 m W·cm^-2、412.12 m W·cm^-2、228.69 m W·cm^-2at 800℃, 750℃, 700℃, 650℃, and the polarization resistance values are 0.86 Ω·cm²、1.13 Ω·cm²、1.74 Ω·cm²、 3.06Ω·cm²at corresponding temperatures. While that of single cell MCO-SDC50 with one-pot hydrothermal synthesis method reaches902.8 m W·cm^-2、618.9 m W·cm^-2、363.8 m W·cm^-2、198.8 m W·cm^-2at800℃, 750℃, 700℃, 650℃, and the corresponding polarization resistance values are 0.85 Ω·cm²、1.18 Ω·cm²、2.0 Ω·cm²、3.73 Ω·cm²,respectively. It is a truism that the composite cathode prepared by above-mentioned two methods all have good electrochemical performance.To further investigate the feasibility of novel composite cathode MCO-SDC, single cells Ni O-SDC/SDC/MCO-SDC50（50:50wt%） and Ni O-SDC/SDC/MCO-SDC70（30:70wt%） were prepared. And the electrochemical performance of cathode with different proportions composite demonstrates that sample with 50wt% SDC has smaller polarization resistance. The maximum power density values of the cell with MCO-SDC50 composite cathode are 929.1 m W·cm^-2、600.6m W·cm^-2、 425.9 m W·cm^-2、 158.6 m W·cm^-2at 700℃, 650℃, 600℃,550℃, respectively, and the polarization resistance values are 0.06Ω·cm²、 0.19 Ω·cm²、 0.43 Ω·cm²、 1.05 Ω·cm²at corresponding temperatures. All these results indicate that novel composite material MCO-SDC50 is remarkably suitable as IT-SOFC cathode.