The Influence Of Ba-deficiency On The Microstructure And Catalytic Activity For Oxygen Reduction Reaction Of Perovskite Metal Oxides

Solid oxide fuel cells?SOFC?technology can meet the country's needs in"clean and efficient use of fossil fuels","off-grid power supply"and"high-value utilization of rare earth resources".The bottleneck problems that restrict the practicality of SOFC are the low activity of cathodic oxygen catalytic reduction?ORR?and poor working stability.This problem is closely related to the microstructure of the cathode coating and its evolution during the operation of SOFC.Our previous research work and other relevant literature reports have confirmed that the introduction of a suitable amount of cation vacancies in the perovskite cathode can optimize the chemical defects of the material and improve the electrochemical performance of the cathode.But so far,the micro-mechanism of the cathodic vacancy control cathode electrochemical performance is still unclear.Based on this,this thesis takes perovskite metal oxides Pr_0.5Ba_0.25-xCa_0.25CoO_3-?and La_0.5Ba_0.5-xCoO_3-?as research objects,and systematically studies the influence of Ba-deficiency on its physical and chemical properties and ORR catalytic performance.In order to prove the cation vacancy control of the microstructure and electrochemical performance of perovskite cathode through relevant work,enrich the knowledge system of perovskite catalyst,and provide the necessary experimental and theoretical accumulation for the development of high-performance ORR catalyst.The main research work of this thesis is introduced as follows:?a?Ba-deficiency can reduce the unit cell volume,thermal expansion coefficient and oxygen vacancy content of Pr_0.5Ba_0.25-xCa_0.25CoO_3-?and La_0.5Ba_0.5-x.5-x CoO_3-?.?b?Ba-deficiency can increase the symmetry of the crystal structure at the operating temperature of SOFC while reducing the volume of the La_0.5Ba_0.5-xCoO_3-?unit cell,and reduce the lattice distortion.?c?Ba-deficiency can significantly improve the conductivity of Pr_0.5Ba_0.25-xCa_0.25CoO_3-?,which may be related to the Ba-deficiency that can reduce the cell volume of Pr_0.5Ba_0.25-x.25-x Ca_0.25CoO_3-?,increase the orbit of O 2p and Co 3d Overlapping,reduce the hole transition barrier and other factors.?d?Ba-deficiency can significantly promote the oxygen exchange process on the surfaces of Pr_0.5Ba_0.25-xCa_0.25CoO_3-?and La_0.5Ba_0.5-xCoO_3-?,which may be related to the Ba-deficiency can inhibit the precipitation of alkaline earth and rare earth elements on the surface of the perovskite cathode.?e?Ba-deficiency can significantly reduce the diffusion barrier of oxygen ions in La_0.5Ba_0.5-xCoO_3-?,and promote the phase conduction process of oxygen ions.However,we also confirmed that the Ba-deficiency will cause a slight decrease in the diffusion coefficient of oxygen ions in Pr_0.5Ba_0.25-xCa_0.25CoO_3-?system,which is not conducive to the bulk conduction process of oxygen ions.The different responses of the two perovskite cathodic oxygen ion conduction processes to Ba-deficiency are closely related to their composition and microstructure.?f?Ba-deficiency can significantly improve the ORR catalytic activity and working stability of Pr_0.5Ba_0.25-xCa_0.25CoO_3-?and La_0.5Ba_0.5-xCoO_3-?.For example,the maximum output power of a single cell based on Pr_0.5Ba_0.25-x.25-x Ca_0.25CoO_3-??x=0.005?at 800°C is 2.084 W/cm²,which is about 15%higher than the original sample.The specific surface polarization resistance?ASR?value of the corresponding symmetric battery at700°C is 0.0349?cm²,which is about 52%lower than the original sample.The ASR growth rate of La_0.5Ba_0.5-x.5-x CoO_3-?at 700°C decreased from 0.72%/h?x=0.000?to 0.13%/h?x=0.025?.