Design And Development Of High-Performance Symmetric Solid Oxide Fuel Cell Electrode Materials

Solid oxide fuel cell（SOFC）is an electrocatalytic device capable of directly converting the chemical energy of a fuel into electrical energy in an efficient and environmentally friendly manner.It has received extensive attention in the energy industry due to its advantages of all-solid-state components,high energy conversion efficiency,fuel flexibility,and low emissions.In recent years,symmetric solid oxide fuel cells（SSOFCs）using the same electrode material as cathode and anode have become the focus of researchers due to their low manufacturing cost,good compatibility between electrolyte and electrode materials,and strong anti-carbon deposition ability.By studying the preparation conditions and methods of symmetric solid oxide fuel cells,this thesis systematically investigates and studies high-performance electrode materials,so as to choose the best electrode materials for symmetric solid oxide fuel cells.The main research contents are as follows:（1）La_0.6Ca_0.4Fe_0.7Ni_0.2Mo_0.1O_3-δ（LCFNM）was used as the electrode material for material evaluation in terms of phase structure,thermal expansion behavior,and conductivity.The electrodes were prepared by ball milling,physical mixing and impregnation methods,and a series of electrochemical performance analyses were performed by constructing symmetric cells and single cells with SDC as the electrolyte.The results showed that the LCFNM samples calcined at 1000°C for 5h under air showed orthogonal chalcogenide structure,and the samples still maintained the original chalcogenide structure after reduction at 750°C for 10h under H₂-Ar gas atmosphere,showing good stability.the TEC test results indicated that the LCFNM samples had good thermal matching with the electrolyte SDC.The conductivity of the LCFNM sample was tested by the four-probe method in the temperature range of 600-800℃in air,and the maximum conductivity value(56.1 S cm^-1)was obtained at 800℃.The electrochemical performance analysis of the electrodes revealed that the electrodes prepared by the dip method had the best ORR and HOR activities.The results of the single-cell performance tests showed that the LCFNM prepared by the impregnation method as the electrode,SDC as the electrolyte,and the electrolyte-supported single cell exhibited the best performance,for example,the maximum power density of the single cell fueled by wet hydrogen gas at800°C was up to 518 m W cm^-2.These results suggest that the LCFNM system material is a potential symmetric solid oxide fuel cell electrode material.（2）La_0.6Sr_0.4Fe_0.7Ni_0.2Mo_0.1O_3-δ（LSFNM）materials were developed by replacing Ca at the A-site with Sr,and the materials were characterized by physical phase,infrared,thermal expansion coefficient,and electrical conductivity.The electrodes were also prepared by ball milling,physical mixing and impregnation methods,and a series of electrochemical performance analyses were constructed for symmetric and single cells with SDC as the electrolyte,respectively.The results showed that the LSFNM samples calcined at 1000°C for 5 h under air showed an orthogonal chalcogenide structure,and the LSFNM samples reduced at 750°C for 10 h under H₂-Ar gas atmosphere still maintained the structural stability.The TEC test of LSFNM samples shows that the electrode material LSFNM is more suitable for the electrolyte SDC and can meet the basic requirements for battery operation.The conductivity of LSFNM samples was tested in the temperature range of600-800°C in air and reached a maximum value of 92.9 S cm^-1at 800°C,which is a great improvement compared with the maximum conductivity of 56.1 S cm^-1of LCFNM under the same conditions.In the impedance spectrum analysis of the symmetric cell,it was also found that the electrode prepared by the impregnation method had the most excellent ORR and HOR activity,and the specific area resistance（ASR）of this symmetric cell at 750°C air was a minimum of 0.19Ωcm².By comparison,it was found that the LSFNM series electrode materials had better ORR and HOR activity than the LCFNM series materials.Finally,single-cell performance tests were performed,and the best single-cell output performance was constructed with electrodes prepared by the impregnation method,which showed a maximum power density of 604 m W cm^-2at 800°C with wet hydrogen as fuel.the LSFNM series materials prepared under the same test conditions and methods showed better cell output performance compared with the LCFNM series materials.These results indicate that the LSFNM series materials are well suited as electrode materials for symmetric SOFC.