Preparation And Electrochemical Performance Of Novel Cathode Materials For Solid Oxide Fuel Cells

Solid Oxide Fuel Cells（SOFCs）possess the features of clean and efficient,green and environmentally friendly,and are products with high conversion efficiency in developing fuel cells.However,SOFCs generally operate under high-temperature conditions,an excellent test for cell materials.Traditional electrode materials use precious metal elements such as cobalt（Co）and nickel（Ni）.Although the conversion efficiency is high,this will not only cause more significant pollution to the environment but also increase the cost of battery construction.One of the hot spots for research on electrode materials for SOFCs is the development of new cathode materials with outstanding performance in low and medium-temperature environments.Numerous studies have shown that strontium molybdate iron-based(Sr₂Fe_1.5Mo_0.5O_6–δ,SFM)cathode materials have high performance.Currently,SFM-based materials have become an emerging cathode material in low and medium temperature solid oxide fuel cells,where doping modification is the main way to enhance the electrical properties of SFM cathode materials.In this paper,doping modification experiments were carried out on Sr₂Fe_1.5Mo_0.5O_6–δcathode materials to investigate the influence of different doping elements and contents on the stability,conductivity,and electrochemical properties of the cathode materials.Using solution combustion methode to synthetise the Sr_2-xBa_xFe_1.5Mo_0.5O_6-δ（SBFM,x=0.3,0.5,0.7,0.9）,Sr₂Fe_1.5-xZn_xMo_0.5O_6-δ（SFZn M,x=0,0.025,0.05,0.075,0.1）,Sr_2-xPr_xFe_1.5Mo_0.5O_6-δ（SPr FM,x=0,0.025,0.05,0.075,0.1）cathode materials.The phase composition of the powders was probed using X-ray diffraction;the microscopic morphology of the powders was observed using scanning electron microscope;the thermal expansion coefficient of the cathode samples was measured using a thermal expansion coefficient tester to investigate its match with the electrolyte material;the electrical conductivity of the samples at different ambient temperatures was measured using the DC four-terminal method;and the electrochemical properties of the symmetric cells were measured using AC impedance spectroscopy.The conclusions show that:The Sr_2-xBa_xFe_1.5Mo_0.5O_6-δ（SBFM,x=0.3,0.5,0.7,0.9）cathode powder has a typical perovskite structure after high-temperature calcination;the microscopic morphology of SBFM powder shows a porous mesh structure;the coefficient of thermal expansion is similar to that of Ce_0.8Gd_0.2O_2-δelectrolyte;the variation pattern of conductivity with temperature is obviously,the conductivity of SBFM can reach the highest point at 450°C,which is 18.5 S/cm;the electrochemical performance test results can prove that the appropriate amount of Ba²⁺doping is beneficial to maintain the catalytic activity of SFM materials and effectively reduce the activation energy required for the reaction.The cathode powder of Sr₂Fe_1.5-xZn_xMo_0.5O_6-δ（SFZn M,x=0,0.025,0.05,0.075,0.1）was analyzed by X-ray diffraction technique and proved to have a typical perovskite structure;the SFZn M powder showed a fluffy and porous spongy shape as shown by the swept surface electron microscopy;the coefficient of thermal expansion and the XRD pattern after co-firing show that SFZn M has better chemical stability with Ce_0.8Gd_0.2O_2-δelectrolyte material;the conductivity of SFZn M can reach a maximum value of 27.3 S/cm at 450°C for the doping amount x=0.05,which is higher than that of SFM;the appropriate doping of Zn²⁺is beneficial to maintain.The appropriate doping of Zn²⁺is conducive to maintaining the catalytic activity of SFM,effectively reducing the activation energy required for the reaction and improving the conductivity of the cathode material.Sr_2-xPr_xFe_1.5Mo_0.5O_6-δ（SPr FM,x=0,0.025,0.05,0.075,0.1）cathode powder also has an apparent perovskite structure;the microscopic morphology of SPr FM powder shows a fluffy and porous character with uniform pores;the appropriate doping of Pr³⁺is conducive to reducing the thermal expansion change rate of the sample,which is easier to match the electrolyte;after co-fired experiments,it can be seen that the SPr FM cathode material has better chemical stability with Ce_0.8Gd_0.2O_2-δelectrolyte.The conductivity and electrochemical performance test results show that Sr_1.95Pr_0.05Fe_1.5Mo_0.5O_6-δmaterial has the best electrical performance,with a maximum conductivity of 32.0 S/cm and the lowest polarisation resistance of 0.266Ω·cm².