Preparation And Performance Study Of（La,Ca）FeO_3-δ Based Solid Oxide Cells Cathode Materials

Solid oxide fuel cell(SOFC)has high energy conversion efficiency and is expected to replace traditional power generation method in the future.The conventional SOFC has problems of poor stability,short service life and high requirements due to its operation at higher temperatures(around 1000℃).Therefore,lowering SOFC working temperature becomes an inevitable trend,however,La0.6Sr0.4Co0.8Fe0.2O3-δ as the main material system of low and medium temperature SOFC oxygen electrode materials have many problems such as high thermal expansion coefficient,high cost and Sr segregation.In this work,Ca-doped LaFeO3-δ the material is chosen as the SOFC oxygen electrode to slove the above problems.First,La1-xCaxFeO3-δ(x=0.1-0.4;LCF)was synthesized by the sol-gel method.The XRD results show that Ca2+ ions are doped into the LaFeO3-δ lattice.The Ca doping was shown by XPS analysis to increase the oxygen vacancy concentration of the material.The conductivity test results showed that the conductivity increased with the increase of Ca doping percentage,and the maximum value of conductivity was 201.2 S cm-1 when x=0.4.The oxygen nonstoichiometric ratio of LCF materials was determined by coulometric titration versus oxygen partial pressure,indicating that LCF does not decompose at lower oxygen partial pressure,but there is a phase structure transition.In addition,the LCF oxygen electrode material exhibited good electrochemical performance as the doping ratio of Ca2+ions increased,with ASR values and power densities of 0.059 Ω cm2 and 1558 mW cm-2 at 850℃,respectively,when x=0.4.However,the single-cell attenuation is greater than that of x=0.3 at x=0.4 during the long-term test.Secondly,in combination with the poor stability of the previous high percentage Cadoped LaFeO3-δ material,its performance is improved by doping four elements(M=Nb,Co,Sb,Ni)in the B-site position of La0.7Ca0.3Fe0.9M0.1O3-δ.The XPS results showed that the Co and Ni doping improved the oxygen vacancies of the material.The electrochemical test results showed that the ASR values and power densities of the Co and Ni doped samples were 0.056,0.039 Ω cm2 and 1466,1604 mW cm-2 at 850℃,respectively.However,the singlecell decay of Ni-doped was greater than that of Co-doped during the long-term test.Therefore,the results indicate that the Co-doped oxygen electrode material has good oxygen catalytic performance and stability.Finally,a strategy of partial substitution of La with different rare earth elements at the A-position of La0.7Ca0.3FeO3-δ was used to improve the electrochemical performance of the material.The results showed that La0.5M0.2Ca0.3FeO3-δ(M=Pr,Nd,Sm,Gd;LMCF)material oxygen electrode material has good electrochemical performance.Among them,Gd has the best performance with ASR value and power density of 0.058 Ω cm2 and 1205 mW cm-2 at 800℃,respectively.During the long-term test,the single-cell decay ratio of La using Sm and Gd partial substitution is smaller than that of La0.7Ca0.3FeO3-δ single-cell decay ratio,and the oxygen electrode materials with Gd substitution have better performance than those with Sm substitution.The results indicate that the strategy of using the rare earth component Gd partially replacing La at the A-site effectively enhances the oxygen catalytic activity and stability of LCF.