Preparation And Properties Of Double Perovskite Cathode Materials For Medium And Low Temperature SOFC

La_1.5Ba_0.1Sr_0.4Co MO_5+?(M=Co,Cu,Fe,Ni)(LBSCM),)cathode materials for medium and low temperature solid oxide fuel cell(IT-SOFC)were synthesized by sol-gel method.The microstructure and electrochemical properties of the materials were studied by X-ray diffraction(XRD),thermal expansion coefficient(TEC),scanning electron microscope(FESEM)and DC four-electrode method.The results of XRD study show that the cathode materials prepared by sol-gel method form a stable layered perovskite structure except LBSCN after calcined at 1000 ^oC for 10 h,and it can be seen that:LBSCM(M=Co)has the best morphology and structure with uniform particle size and many pores through SEM observation of the cross section of cathode strip.The electrical conductivity test results show that LBSCM series cathode materials have high electrical conductivity at 400-800 ^oC,the largest of which is LBSCM(M=Co)reaching 1204 S cm^-1 at 400 ^oC.The average coefficient of thermal expansion(TEC)of cathode material is 18.471×10^-6 K^-1(LBSCM(M=Co)),17.3017×10^-6 K^-1(LBSCC),17.6407×10^-6 K^-1(LBSCF),16.503×10^-6 K^-1(LBSCN),17.1306×10^-6 K^-1(LBSCCF),is higher than that of commonly used electrolyte SDC(TEC is 12.6×10^-6 K^-1),and the thermal expansion test results are passed.It can be seen that the thermal expansion coefficient of LBSCM cathode materials doped with Cu,Fe and Ni decreases obviously.Preparation of cobalt-free cathode La_1.5Ba_0.1Sr_0.4Cu₂O_5+?(LBSC),cobalt-based cathode La_1.5Ba_0.1Sr_0.4Co_0.8Cu_1.2O_5+?(LBSCC),La_1.5Ba_0.1Sr_0.4Co_0.8Cu_0.5Ni_0.7O_5+?(LBSCCN),La_1.5Ba_0.1Sr_0.4Co_0.8Cu_0.5Cr_0.7O_5+?(LBSCCC),La_1.5Ba_0.1Sr_0.4Co_0.8Fe_0.7Ni_0.5O_5+?(LBSCFN),composite cathode La_1.5Ba_0.1Sr_0.4Co_0.8Fe_0.7Ni_0.5O_5+?-Sm_0.2Ce_0.8O_2+?(LBSCFN-SDC)material by sol-gel method.The prepared cathode materials were tested and characterized by X-ray diffraction(XRD),thermal expansion coefficient(TEC),scanning electron microscope(SEM)and electrical conductivity.The XRD results show that the series of cathode materials prepared by sol-gel method form a stable layered perovskite structure after calcination at 1000 ^oC for 10 h,and there is only a diffraction peak of pure cathode LBSCFN and electrolyte SDC in LBSCFN-SDC spectra,indicating that there is no reaction between LBSCFN and electrolyte SDC.SEM observed that the cathode powders of LBSCCN and LBSCCC are uniform in size,compact in arrangement and high in crystallinity.The test results of electrical conductivity show that the electrical conductivity of other cathode materials is greater than 100 S cm^-1,except that LBSCFN-SDC is 94 S cm^-1 at 800 ^oC,and the highest conductivity is 730 S cm^-1 at 400 ^oC.The average thermal expansion coefficients of cathode materials are 10.9468×10^-6 K^-1(LBSC),17.276×10^-6K^-1(LBSCC),17.0072×10^-6 K^-1(LBSCCN),19.1445×10^-6 K^-1(LBSCCC),17.2143×10^-6 K^-1(LBSCFN)and 12.7604×10^-6 K^-1(LBSCFN-SDC).It can be seen that the thermal expansion coefficient of cathode materials decreases obviously after doping Cu,Fe and Ni,and the thermal expansion coefficient of doped Cr is the highest.The TEC of cobalt-free cathode LBSC is 10.9468×10^-6 K^-1,which is lower than that of electrolyte SDC(TEC(12.6×10^-6K^-1).Then the composite cathode LBSCFN-SDC,was prepared by mixing LBSCFN and SDC at a mass ratio of 1:1.The thermal expansion coefficient was 12.7604×10^–6 K^-1,which was well matched with the common electrolyte SDC.NdBa_0.5Sr_0.5Ni_0.7Co_1.3-xCu_xO_5+?cathode materials were prepared by sol-gel method and characterized by X-ray diffraction(XRD),thermal expansion coefficient(TEC),scanning electron microscope(SEM)and electrical conductivity.The XRD results showed that the NBSNCC cathode powders formed a stable layered perovskite structure after calcined at 1000 ^oC for 10 h,and SEM observed that the size of the particles in the cross section of the cathode strip was uneven,there were many pores,and the crystallization was general.The test results of electrical conductivity show that NBSNCC exhibits a metal-like conduction mechanism at 400-800 ^oC,which accords with the variation characteristics of electrical conductivity of double perovskite cathode materials.The largest conductivity is that NdBa_0.5Sr_0.5Ni_0.7Cu_1.3O_5+?reaches 240 S cm^-1 at 400 ^oC,and when x is0.3,0.8,1,the conductivity is lower than 100 S cm^-1,and when x is 0.3,0.5,1.3,the conductivity is more than 100 S cm^-1.When NdBa_0.5Sr_0.5Ni_0.7Cu_1.3O_5+?is 0.3,0.5,1.3,the conductivity is more than100 S cm^-1,and when NdBa_0.5Sr_0.5Ni_0.7Cu_1.3O_5+?is 0.3,0.5,1.3,the conductivity is more than 100 S cm^-1.The results of thermal expansion coefficient study show that with the increase of Cu doping content,the thermal expansion coefficient of NBSNCC series cathode materials decreases obviously,of which the lowest is NdBa_0.5Sr_0.5Ni_0.7Co_0.3Cu O_5+?,which is 15.6355×10^–6 K^-1,which matches well with electrolyte SDC.