Researches Of BaFe_0.9Bi_0.1-xSc_xO_3-δ Cathode Material For Intermediate Temperature SOFC

Solid oxide fuel cells（SOFCs）can convert chemical energy of various fuels to electrical energy directly.It is one of the cleanest and most efficient power sources.Decreasing the operating temperature range to intermediate and low temperature range is an inevitable trend,amoung which the electrochemical performance of cathode at low temperature is a key restrictive factor.BaFe O3 have disordered oxygen vacancies.In addition,more Fe resources and lower than cobalt ions i s available.Therefore,BaFeO₃-based perovskite oxides are chose as the researching object.Co-doping of bismuth and scandium is adopted to stabilize its cubic phase,in which the content of bismuth is lower than 10 mol%.BaFe_0.9Bi_0.1-xSc_xO_3-δ（BFBSx）cathode are synthesized via a sol-gel method and their structures and performance are characterized.XRD results show that the most suitable calcining temperature for the preparation of BFBSx is 1000 ℃.Cubic phases of BaFeO3 are obtained readily.The cubic phased is kept stableeven at room temperature because of the co-doping of bismuth and scandium.With the increase of Sc contents,the cell volume decreases first and then increases,thus leading to the largest cell volume of BFBS0.04.The cathode has a poor compatibility with SSZ but a good compatibility with GDC.When the content of Bi is 10 mol%,the oxygen vacancy content reaches the largest value.The shrinkage rate of BFBSx achieves its peak faster with more Sc doping content.When x is 0.04,it archive a TEC of 21.72×10-6 K-1 within the temperature range of 50 700 ℃,which is 18 % lower than that of BFBS0.The electrical conductivity of BFBSx is accorded with the small polaron hopping mechanism.With the increase of Sc contents,its electrical conductivity decreases first and then increases,with its maximum conductivity of 9.41 S cm-1 at 500 ℃.Y0.5Bi1.5O_3-δ（YSB）is used as interlayer to prevent reactions between the cathode and SSZ electrolyte.The best preparation conditions of the cells are confirmed using the electrochemical impedance spectrum.The optimum calcining temperature of YSB as an interlayer is 950 ℃,which is also the optimum for the cathode.The lowest polarization of BFBS0.04 is 0.129 Ω cm2 at 750 ℃.The activation energy for oxygen reduction reaction of BFBS0.06 is only 0.70 e V,which is much lower than that of iron base cathode.The Ni-SSZ|SSZ|YSB|BFBS0.04 single cell archives its maximum power density of 0.93 W cm-2 at 850 ℃.The composite cathodes comporising BFBSx and 30 wt% GDC are synthesized.The polarization resistance of BFBS0.05-GDC on YSB is 0.091 Ω cm2,while it is 0.119 Ω cm2 on GDC at 750 ℃.These are lower by 57.5 % and 69.2 % respectively than the non-composite BFBS0.05 cathodes.