Performance Improvement Of Sr₂Fe_1.5Mo_0.5O_6-δ For Intermediate-temperature Solid Oxide Fuel Cells

Solid oxide fuel cells （SOFCs） have the features of clean and efficient, and thereforehave a wide range of applications. But such high operating temperature （800-1000oC）causes some problems, as poor stability and performance degradation. It’s very necessary todevelop inter-temperature SOFCs （IT-SOFCs）, which would be operatured at lowertemperature range600-800oC. Thus the key is to develop high catalytic activity electrodematerials at lower temperature range. The perovskite Sr₂Fe_1.5Mo_0.5O_6-δ（SFM） has highconductivity and catalytic activity, so SFM should be an ideal electrode material forIT-SOFCs.This work focused on the performance improvement of Sr₂Fe_1.5Mo_0.5O_6-δas anodematerla. It was expected to improve the electro-catalytic activity of Sr₂Fe_1.5Mo_0.5O_6-δin H2and CH4fuels by metal-doping. Because of approximate radius or ion valences, transitionmetal elements （Sn, Mn, Nb, Cu, Co, Zn, V） are chosen to substitute Fe element partially. Aseries of Sr2Fe1.4X0.1Mo0.5O6-（X=Sn, Mn, Nb, Cu, Co, Zn, V） anode materials are preparedby one-step combustion technology. These materials exhibit clearly net structure andhomogeneously distributed, and also have ideal perovskite crystal structure except SFVM.The electrochemical impedance spectroscopy （EIS） results suggest that SFSnM exhibitesthe lowest polarization resistance （Rp） in H2, which is0.86Ω cm2at800oC. Meanwhile,SFSnM also possesses the highest conductivity （σ is20.99S cm-1）. Furthermore,thedischarge performance was measured by an electrolyte-supported single cell with a SFSnManode. The maximum power densities of SFSnM∣LSGM∣LSCF are630and420mWcm-2in H2and CH4at800oC.Niobium doping is evaluated as a means of enhancing the electrochemicalperformance of Sr₂Fe_1.5Mo_0.5O_6-δ（SFM） as cathode material. As the radius of Nbapproximates that of Mo and exhibits+4/+5mixed valences, the Nb substitution isexpected to increase the oxygen vacancies concentration and improve the catalytic activity.A series of Sr2Fe1.5Mo0.5-xNbxO6-（x=0.05,0.10,0.15,0.20） cathode materials are preparedand the phase structure, chemical compatibility, microstructure, electrical conductivity,polarization resistance and power generation are systematically characterized. Among theseries of samples, Sr2Fe1.5Mo0.4Nb0.10O6-δ（SFMNb0.10） exhibits the conductivity value of30 S cm-1at550oC, and the lowest area specific resistance of0.068Ω cm2at800oC.Furthermore, an anode-supported single cell incorporating a SFMNb0.10cathode presents amaximum power density of1102mW cm-2at800oC. Furthermore no obvious performancedegradation is observed over15h at750oC with wet H2（3%H2O） as fuel and ambient airas the oxidant. These results demonstrate that SFMNb0.10shows great promise as a novelcathode material for IT-SOFCs.