Properties Of SrFeO_3-δ-based Cathode Materials For Intermediate-temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are solid-state energy conversion devices;these devices have attracted considerable attention because of their high-energyconversion efficiency, low emission of pollutants, and good fuel flexibility.Conventional high-temperature SOFCs must be operated at temperatures of around1000°C. Such high operating temperatures cause many serious physical andchemical issues. Therefore, it is extremely necessary to develop new cathodematerials that have a high electrochemical performance for the oxygen reductionreaction of intermediate-temperature SOFCs (IT-SOFCs). Recently, SrFeO3-based cubic perovskite oxides, Bi0.5Sr0.5FeO3, SrFe0.9Sb0.1O3, SrFe1xMoxO3,and SrFe0.9Nb0.1O3have been demonstrated to have good electrochemicalperformances as potential cathode materials for IT-SOFCs. To extend our researchwork, the effects of Ti, Al, Cu substitution for Fe on the phase structure, electricalconductivity, TEC, and cathode performance of the SrFe1xMxO3(M=Ti, Al, Cu)used as a potential cathode material for IT-SOFCs have been investigated in detail.Perovskite cathode materials of SrFe1xTixO3(SFTx, x=0.00-0.15) wereprepared by a solid-state reaction. No impurity peaks are observed in the XRDpatterns, suggesting that all the SFT materials crystallize in a single-phase perovskitestructure. The SFT samples sintered at1300°C for10h are very dense. The grain sizes gradually decrease with an increase in the Ti contents, suggesting that thesubstitution of Ti for Fe restrains the grain growth. The SFT cathodes have a goodchemical compatibility with the LSGM and SDC electrolytes at temperatures below1000°C. The average TEC values of the SFT samples are26.5×106,24.9×106,23.6×106, and22.9×106K1for x=0.00–0.15between30°C and1000°C in air.The maximum electrical conductivity value was72S cm1for the x=0.05sample inthe temperature650°C. The polarization resistances of SFTx(x=0.00-0.15) cathodeswere0.138,0.118,0.150and0.175cm2at700oC, respectively. The peak powerdensities of a single-cell for SFTx(x=0.00-0.15) cathodes were446,475,439and432mW cm2at800oC, respectively. The SrFe0.95Ti0.05O3--SDCx composites wereassessed as IT-SOFC cathodes. The TEC of SrFe0.95Ti0.05O3--SDCx compositecathodes decreased as the SDC content increased. The average TEC values of theSFT5-SDCx composite cathodes are21.8×106K1,19.3×106K1and17.3×106K1for x=0.00–0.15between30°C and1000°C in air. The introduction of SDCinto SrFe0.95Ti0.05O3-cathode improved the electrochemical performance of thecomposite cathodes. The peak power densities of a single-cell with SrFe0.95Ti0.05O3--SDC20composite cathode was605mW cm2at800oC. The results indicated that theSrFe0.95Ti0.05O3--SDC20composite material is promising for application IT-SOFCs.Perovskite cathode materials of SrFe1xAlxO3-(SFAx, x=0.05-0.20) wereprepared via the glycine-nitrate process (GNP). The SrFe1xAlxO3-(SFAx, x=0.05-0.20) oxides sintered at1350oC for10h crystallized in a single phase perovskitestructure. The unit-cell parameter increases with an increase in the Al contents.The SFA cathodes have a good chemical compatibility with the LSGM electrolyteat temperatures below950°C. The electrical conductivity of the x=0.10sampleexhibits a maximum. There are the orthorhombic-to-cubic structural phase transitionin the SFA oxide (x=0.00,0.05). The average TEC values of the SFA samples are 27.2×106,25.7×106,22.5×106, and20.5×106K1for x=0.05–0.20between30°C and1000°C in air. The polarization resistances of SFAx(x=0.05-0.20)cathodes were0.15,0.11,0.12, and0.13cm2at700oC, respectively. The peakpower densities of a single-cell for SFAx(x=0.05-0.20) cathodes were630,700,584,and523mW cm2at800oC, respectively. The results indicated that the x＝0.10material is promising for application IT-SOFCs.Perovskite cathode materials of SrFe1xCuxO3-(SFCx, x=0.10-0.30) wereprepared via the GNP. The SrFe1xCuxO3-(SFCx, x=0.10-0.30) oxides sintered at1050oC for10h crystallized in a single phase perovskite structure. The unit-cellparameter increases with an increase in the Cu contents. The SFC cathodes havea good chemical compatibility with the LSGM electrolyte at temperatures below950°C. The maximum electrical conductivity value was192S cm1for the x=0.10sample in the temperature500°C. The average TEC values of the SFC samples were24.5×106,24.8×106, and23.0×106K1for x=0.10–0.30between30°C and900°C in air. The polarization resistances of SFCx(x=0.10-0.30) cathodes were0.072,0.085and0.10cm2at700oC, respectively. The peak power densities of asingle-cell for SFCx(x=0.10-0.30) cathodes were606，560and525mW cm2at800oC, respectively. The results indicated that the x＝0.10material is promising forapplication IT-SOFCs.