Preparation And Performance Research Of BaFeO_3-δ-based Intermediate Temperature Solid Oxide Fuel Cell Cathode Materials

With the depletion of energy and the deterioration of the environment,the development and utilization of high-efficiency and environment-friendly energy have been widely studied.Solid oxide fuel cells（SOFCs）are used to improve energy depletion and environmental degradation as an efficient and clean energy conversion device.The working temperature of SOFC is in the range of 700～1000℃.When the temperature exceeds 850℃,it has strict requirements on the constituent materials,which will also reduce the SOFC life and hinder the commercial development of SOFC.Lowering the temperature will rapidly increase the cathode polarization resistance and reduce cell performance,so it is particularly necessary to develop cathode materials with high catalytic activity in the mid-temperature region（600–800℃）.This paper takes BaFeO₃perovskite oxide as the research object,and designs SOFC cathode materials with high oxygen reduction catalytic activity and CO₂tolerance through Hf and Co doping,composite cathode,surface modification and other methods.BaFeO_3-δ-based perovskite oxides are selected due to the large ionic radius of Ba at the A site and the variable oxidation and spin states of Fe at the B site with high oxygen vacancy concentration,which can improve the catalytic activity of the material.Perovskite oxides containing alkaline earth metal ions are prone to CO₂poisoning when used as SOFC cathode materials,which affects the performance of the cell.The Lewis acid-base theory regards the reaction between materials and CO₂as the reaction between bases and acids.Increasing the acidity of the material can increase the difficulty of the reaction.High-valence Hf⁴⁺is incorporated because it can improve the overall acidity of the material.The specific work is as follows:First,Doping Hf at the Fe site of BaFeO₃,The high-valence Hf⁴⁺doping not only enables the material to obtain a highly symmetrical cubic phase structure that is conducive to oxygen ion transport,but also improves the overall acidity of the material and obtains excellent CO₂tolerance（the R_pdropped to 0.12055Ωcm²after removing 10 Vol%CO₂）.In order to improve the catalytic activity of the material,Co and Hf co-doped BaFeO₃perovskite oxides(Ba Co_xFe_0.9-xHf_0.1O_3-δ,x=0.1,0.15,0.2)were prepared,with variable valence of Co/Fe ions.The state can promote the migration of oxygen ions and obtain excellent electrochemical performance.Ba Co_0.2Fe_0.7Hf_0.1O_3-δobtained the best electrochemical performance(R_pwas 0.04041Ωcm²at 800°C,the peak power density of the single cell was 1010.4 m W cm^-2,and the total degradation rate in the long-term stability test was 0.009%h^-1).In addition,Ba Co_0.2Fe_0.7Hf_0.1O_3-δstill maintains excellent CO₂tolerance（R_precovers to 0.04510Ωcm²after removing 10 Vol%CO₂）.To further optimize Ba Co_0.2Fe_0.7Hf_0.1O_3-δ,Composite materials,A-site defects,and polarizationtreatmentsareapplied.Thecompositecathode Ba Co_0.2Fe_0.7Hf_0.1O_3-δ+Ce_0.8Gd_0.2O_2-δmake the thermal expansion coefficient decreases,R_pdecrease（0.04023Ωcm²at 800°C）,and the peak power density increases(1385.8 m W cm^-2at 800°C).In the surface modification,the A-site defect material Ba_0.97Co_0.2Fe_0.7Hf_0.1O_3-δproduced a small amount of nanoparticles with smaller size on the surface,but the R_pdid not decrease.The polarization treatment produces a large number of nanoparticles on the surface of the material,which increases the specific surface area and improves the electrochemical performance（Before and after polarization,the R_pat 800°C are 0.04106Ωcm²and 0.03833Ωcm²,respectively）.Through a series of operations,we obtained SOFC cathode materials with excellent oxygen reduction catalytic activity and CO₂tolerance in the mid-temperature region,which contributed to the development of SOFC.