Preparation And Properties Of BiFeO_3-δ-based SOFCs Cathode Materials By Electrospinning

Solid oxide fuel cells（SOFCs）have attracted much attention due to their environmental protection and high efficiency.The middle and low temperature is the main development trend.However,with the decrease of operating temperature,the polarization resistance of cathode increases sharply,which leads to the decrease of cell performance.Perovskite-type cobalt-free oxide BiFeO₃（BFO）is considered as an important candidate material for SOFCs cathode at medium and low temperature due to its high thermal stability,high chemical stability,low thermal expansion coefficient,non-toxic and so on.But its performance is lower than that of cobalt-based cathode material.This paper intends to improve the catalytic activity of BFO cathode by means of nanofiber morphology construction,element doping and surface modification.The main research contents and results are as follows:（1）Bi_0.8M_0.2FeO_3-δ（BMFO,M=Mg,Ca,Sr）nanofibers were prepared by electrospinning,and the electrochemical performance was studied.The results show that the polarization resistance（R_p）of BFO can be reduced by doping Ca or Sr at A-site,while Mg doping will lead to the increase of R_p.Among them,Sr doping is the most beneficial to the reduction of cathode polarization resistance.The R_pof Bi_0.8Sr_0.2FeO_3-δis 0.084Ω·cm² measured at 700℃,which is only 17%（0.496Ω·cm²）of the undoped cathode,and it shows excellent electrochemical performance.The maximum power density(P_max)of NiO-SDC|SDC|Bi_0.8Sr_0.2FeO_3-δanode supported single cell is 583.16mW·cm^-2at 700℃.After testing at 600℃for 50 h,the performance basically did not attenuated（about 0.7V）,which shows good long-term stability.（2）Bi_1-xSr_xFeO_3-δ（BSFO,x=0.1,0.2,0.3,0.4）nanofiber cathode materials with different Sr doping ratios were prepared by electrospinning technology.The results show that when Sr doping ratio x=0.3,BSFO nanofibers have the lowest R_p（0.137Ω·cm²,650℃;0.061Ω·cm²,700℃）,which is only about 20%of the same component nanopowders（650℃,0.771Ω·cm²;700℃,0.282Ω·cm²）.The P_maxof Ni O-SDC|SDC|BSFO（x=0.3）single cell can reach 663.81 m W·cm^-2at 700℃.In addition,after testing at 600℃for 50 h,the voltage is basically stable at about 0.75 V,which shows good long-term stability.（3）Bi_0.7Sr_0.3FeO_3-δwas selected as the research object,and BSFO-Ag composite nanofiber cathode was prepared by impregnation and rapid sintering process.The results show that the polarization resistance of BSFO-Ag composite cathode is significantly reduced.When the test temperature is less than or equal to 650℃,R_pdecreases with the increase of immersion times.When the test temperature is above650℃,R_pfirst decreases and then increases with the increase of immersion times.When the number of immersion times is 5,R_preaches the minimum（0.039Ω·cm²,700℃）,which is 64%of that of the BSFO cathode.The P_maxof Ni O-SDC|SDC|BSFO-Ag5 single cell at 700℃is 766.24mW·cm^-2and R_pis 0.06Ω·cm².In addition,after testing at 600℃for 50h,the voltage is basically stable at about 0.75V,which shows good long-term stability.