Electrochemical Properties Of Sr_2-xLa_xFe_1.5Mo_0.5O_6-δ Electrode Materials For Solid Oxide Cell

Currently,the shortage of fossil energy and global warming can be solved by developing new materials and improving conversion efficiency.Solid oxide fuel cell（SOFC）has some advantages compared with other energy conversion devices,such as high efficiency,fuels diversity and so on.Carbon dioxide is a major factor in the greenhouse effect and global climate change.How to reduce emissions or efficiently convert carbon dioxide has also attracted extensive research.Solid Oxide Electrolysis Cell（SOEC）is a promising technology that can convert carbon dioxide into valuable fuels such as carbon monoxide and can also be used as an energy storage technology.Considering that Sr₂Fe_1.5Mo_0.5O_6-δis a double perovskite material with good redox stability,it can be used as both cathode and anode of SOFC.In addition,Sr₂Fe_1.5Mo_0.5O_6-δcan also be used as SOEC cathode for CO₂ electrolysis However,its catalytic activity is low.La element was doped at Sr-site to improve the electrochemical performance in this thesis.The main contents and conclusions are as follows:（1）Sr_2-xLa_xFe_1.5Mo_0.5O_6-δperovskite materials with different La doping contents were synthesized by glycine-citric acid method and used as a symmetric electrode for SOFC.Electrochemical performance under various fuels were evaluated.XRD results show that pure phase can be obtained when the La content is lower than 10%,and Sr_2-xLa_xFe_1.5Mo_0.5O_6-δhas good chemical compatibility with the electrolyte La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ（LSGM）.Furthermore,the conductivity and polarization impedance test indicate that Sr_2-xLax Fe_1.5Mo_0.5O_6-δis more suitable as an anode material for SOFC.When using H₂,CO,CH₄and C₃H₈ as fuels,the peak power densities of the SLFM10symmetrical cells at 850℃are 769,561,439 and 653 m W cm^-2,respectively.（2）The electrochemical performance of Sr_2-xLa_xFe_1.5Mo_0.5O_6-δcathode of SOEC for pure CO₂ electrolysis was investigated.The ECR results show that the introduction of La improves the oxygen surface exchange coefficient（K）and bulk diffusion coefficient（D）.At700℃,the K values of SFM,SLFM5 and SLFM10 are 9.71×10^-6,2.03×10^-5 and 3.39×10^-5cm² s^-1,respectively,while the D values are 6.66×10^-7,7.87×10^-7 and 1.18×10^-5 cm² s^-1.The polarization resistances of the SLFM10 symmetric cells at 850,800,750 and 700℃are0.180,0.265,0575 and 2.281Ωcm²,respectively.In the end,the LSGM-supported electrolyzer with SLFM10 as the cathode achieves a current density of-2763 m A cm^-2at850°C at 1.5 V,which is higher than that of the undoped SFM cathode and other previously reported cathode materials.