Preparation And Characterization Of Novel Ca-doped Sr₂Fe_1.5Mo_0.5O_6-? Cathode For SOFC

Solid oxide fuel cell?SOFC?has received worldwide attention,which is a new environmentally friendly and high efficiency energy conversion device.The high operating temperature from 800 ? to 1000 ? of high-temperature SOFC will result in many problems,such as the choice of materials,thermal match between the adjacent material and chemical compatibility,electrode sintering and mechanical properties of cells.Decreasing the operating temperature is one of the improved methods.Therefore,it is necessary to develop intermediate temperature solid oxide fuel cells?IT-SOFC?.Cathode is one of the key components to realize intermediate temperature solid oxide fuel cells.The perovskite Sr₂Fe_1.5Mo_0.5O₆?SFM?has high conductivity and catalytic activity.Therefore,this paper focuses on SFM as a starting point to modify material and study the properties.In this paper,the partial substitution of atomic elements from the A site of a perovskite is investigated in order to develop cathode materials for solid oxide fuel cell applications.Herein,Sr_2-xCa_xFe_1.5Mo_0.5O_6-??SCFM?,compounds were investigated by characterizing structural properties,chemical compatibility,electrical properties,electrochemical performance and stability.The XRD patterns indicated that there is a decrease of cell volume with the increase of Ca content.All materials exhibit clearly net structure and homogeneously distributed.The increasing of Ca substitution results in the decrease of thermal expansion coefficient.X-ray photoelectron spectroscopy analysis suggests that Ca doping significantly affects the Fe²⁺/Fe³⁺and Mo⁶⁺/Mo⁵⁺ratios.For a doping level of x=0.4,the sample showed the lowest interface polarization?R_p?,the highest conductivity and a maximum power density of 1.26 W·cm^-2 at 800 ?.It was concluded that the partial replacement of Sr by Ca improves the conductivity,electrochemical performance and decreases thermal expansion coefficient of SFM cathodes,therefore it is possible to improve the performance of cathode for IT-SOFCs applications.In this work,the SCFM-SDC composite cathode is synthesized by the method of a facile one-step combustion method.XRD results show that SCFM-SDC has identical pure perovskite crystal structure and no impurity phases.The microstructure analysis of samples clearly shows homogeneous pore dimensional network structure.Furthermore,with the increased content of SDC,the conductivity and thermal expansion coefficient of the composite cathodes decrease gradually.The composite cathode has optimal electrochemical performance with low polarization resistance?R_p?with 40%mass fraction of SDC.And at the working temperature range from 650 ? to 800 ?,the Rp are 0.091,0.148,0.376,0.832?cm²,respectively.Therefore,the discharge performance was measured by preparing single cell with SS40 composite cathode.The maximum power density of NiO-YSZ|YSZ|SDC|SCFM-SDC40 single cell is 1.06 W cm^-2 at 800 ?.These results suggest that SCFM cathode materials are excellent candidates for intermediate temperature solid oxide fuel cells applications.