Ln₂（Ln=Sm,Eu）M（M=Cu,Fe）O₄ Material Doping Modification,Crystal Structure And Material Properties Study

Solid oxide fuel cells（SOFCs）are of great interest due to their high energy conversion efficiency,low pollutant emissions and good fuel suitability.K₂NiF₄-type chalcogenide materials are a class of mixed electron-ion conductors with high oxygen ion diffusion and exchange coefficients,good electron conductivity and thermal expansion coefficients matching the electrolyte,which can as potential electrode materials for Intermediate temperature solid oxide fuel cells（IT-SOFCs）.Based on Ln₂CuO₄（Ln=Eu,Sm）materials,this thesis investigates the structural and performance changes by doping modification of A and B sites,respectively,to provide a new idea for the cathode materials of SOFCs.Eu_2-xK_xCuO₄（0≤x≤0.3）、Sm_2-xK_xCuO₄（0≤x≤0.3）and Sm_1.9K_0.1Cu_1-xFe_xO₄（x=0.1,0.3,0.5）materials were prepared by citric acid-nitrate method,characterized and structurally analyzed,and their cathode materials as IT-SOFCs cathode materials were evaluated.The electrochemical performance of IT-SOFCs cathode materials was evaluated.The main research and experimental results of this paper are as follows:First,the Eu_2-xK_xCuO₄（0≤x≤0.3）series materials were studied in this paper.The results show that the Eu_2-xK_xCuO₄ series materials form a K₂NiF₄-type phase structure after roasting at 800°C for 6 h.The Rietveld structure refinement results show that the oxide crystals belong to the tetragonal phase structure,I4/mmm space group.When the doping amount x=0.1,Eu_1.9K_0.1CuO₄ has the highest non-chemometric oxygen contentδ=-0.4707and the highest vacancy oxygen content.The electrochemical test results showed that the polarization resistance R_p（2.12Ω?cm²）of Eu_1.9K_0.1CuO₄ was the smallest at 750°C in air atmosphere,and the lowest polarization overpotential 139 mV was obtained at the cathode when the current density was 30 mA?cm^-2,which indicated the best oxygen-catalyzed reduction performance of the electrode.Density of States（DOS）indicates that the conduction band intersects the valence band at the Fermi plane and the compound has typical metallic properties.Secondly,Sm_2-xK_xCuO₄（0≤x≤0.3）materials prepared using the same conditions described above basically form a single phase of K₂NiF₄-type,and the Rietveld structural refinement shows that the oxide crystals belong to a tetragonal phase structure with a space group of I4/mmm.When the doping amount x=0.1,Sm_1.9K_0.1CuO₄ has the highest non-chemometric oxygen contentδ=-0.4699 Electrochemical tests showed that the Sm_1.9K_0.1CuO₄ polarization resistance R_p（0.90Ω?cm2）was the smallest in air atmosphere at 750°C,and the cathode had the best catalytic performance with the lowest polarization overpotential of 151 mV at a current density of 35 mA?cm^-2.DFT calculations showed that the Fermi DFT calculations show that the conduction band intersects with the valence band at the Fermi surface and the material exhibits typical metallic properties.Finally,the Sm_1.9K_0.1CuO₄ series was prepared by doping its B-site with Fe based on the above studied optimal performance Sm_1.9K_0.1Cu_1-xFe_xO₄（x=0.1,0.3,0.5）materials.XRD showed that the heterophase content in the samples increased with increasing Fe doping.Electrochemical tests show that the Sm_1.9K_0.1Cu_0.9Fe_0.1O₄ cathode material has the lowest polarization resistance R_p（0.53Ω?cm2）in air at 750°C,with a minimum polarization overpotential of 190.9 mV at a current density of 20 m A?cm^-2.DFT calculations show that the presence of the Fermi surface at the The doping of Fe provides orbital electrons to the top of the conduction band,which enhances the electronic conductivity of the material.