High-temperature Electrochemical Performance And Oxygen Reduction Reaction Of Bi_0.5Sr_0.5FeO_3-?-based Cathode Catalysts

The perovskite oxides with mixed oxygen ionic-electronic conduction(MIEC)properties are the potential cathode candidates for solid oxide fuel cell(SOFC).Type cobalt-based perovskite MIEC materials,exhibit excellent electrocatalytic performance for the oxygen reduction reaction(ORR).However,these cobalt-based cathodes encounter some drawbacks like poor chemical stability,inadequate compatibility with the electrolyte material,and easy evaporation of cobalt.Therefore,developing cobalt-free cathodes with excellent electrocatalytic activity is a major target for practical applications of SOFCs.In recent years,iron-based oxides have attracted great attention because of their low cost and excellent electrochemical properties.In this paper,the porperties of a mixed ion-electronic conductor(MIEC)Bi_0.5Sr_0.5FeO_3-? with single perovskite structure are modified by doping high valence cations Mo⁶⁺,V⁵⁺and W⁶⁺into B site.Bi_0.5Sr_0.5Fe_1-xMo_xO_3-?(BSFMx,x=0.025,0.05),Bi_0.5Sr_0.5Fe_1-xV_xO_3-?(BSFVx,x=0.025,0.05 and 0.075),Bi_0.5Sr_0.5Fe_1-xW_xO_3-?(BSFWx,x=0.025,0.05,0.075 and 0.1)were synthesized by high-temperature solid-state method,respectively.The physical and electrochemical properties of the materials were studied by X-ray diffraction(XRD)analysis,thermal expansion(TEC)analysis,electrical conductivity test,micro-morphology(SEM)analysis and so on.BSFMx,BSFVx and BSFWx cathode materials all are high valence doping and have similar properties.The main work are as follows:(1)The cathode materials are crystallized in a single cubic structure with Pm3m space group,and the structure is stable.(2)The cathode materials not only showed a superior thermal stability and chemical compatibility with CGO(Ce_0.9Gd_0.1O_1.95)electrolyte,but also have a suitable coefficient of expansion,which ensures the good operation of the components under high temperature operation.(3)BSFMx,BSFVx and BSFWx cathode materials have excellent electrocatalytic activity.For example,BSFMx achieves the lowest polarization resistance of 0.12 ? cm² at 700? in air,and the maximum peak power density of 1.07Wcm^-2 at 700?.BSFV0.05 has the highest lowest polarization resistance(Rp)of 0.076 ? cm²,and a maximum power density of 1.157Wcm^-2 at 700?.At 700?,the polarization resistance of BSFW0.025 is only 0.076 ? cm²,and the peak power density is 1.27Wcm^-2.(4)The test of CO₂ tolerance and ABE calculation show that BSFMx,BSFVx and BSFWx have better CO₂ durability than parent material Bi-(0.5)Sr_0.5Fe_xO_3-?(BSF)(5)Combined with oxygen partial pressure test,DRT analysis and capacitance(C)and frequency(f)calculation,it can be concluded that the oxygen reduction rate control step of these oxides is oxygen adsorption and dissociation...