The Preparation And Properties Of CeO₂ Based Electrolyte Doped With Scandium Oxide And Dysprosium Oxide

Among the traditional SOFC electrolyte materials,Y₂O₃ stabilized ZrO₂?YSZ?is the most widely used electrolyte ceramic material,but because YSZ only has high conductivity at high temperature?1000??,with the decrease of temperature the conductivity reduced.The high temperature operation is not conducive to the chemical compatibility and the matching of the thermal expansion coefficient of the electrolyte and the electrode.For the battery stack,it is not conducive to the development of the connecting material and the sealing material,which not only increases the manufacturing cost of the battery,but also accelerates the fuel cell system ageing.The doped CeO₂-based electrolyte material has higher conductivity than YSZ in the range of 500?-800?.Therefore,the doped CeO₂-based electrolyte material has considered to be the most promising SOFC electrolyte material.Among of them,Samarium oxide and gadolinium oxide doped CeO₂ showed higher conductivity at low and medium temperatures.However,CeO₂ is easily reduced under reducing atmosphere or low oxygen partial pressure,which produces electronic conductance,resulting in internal short circuit,which reduces the open circuit voltage and output performance of the battery.The sol-gel method was used to synthesize Dy₂O₃ and Sc₂O₃ single-doped and co-doped CeO₂-based electrolyte materials.The phase,surface morphology,oxygen vacancy,conductivity,electronic conductance and thermal expansion coefficient were determined by polycrystalline X-ray diffractometry?XRD?,scanning electron microscopy?SEM?,Raman spectroscopy,electrochemical workstation and thermal dilatometer.With a view to contributing to the mid-low temperature and commercialization of SOFC technology.When the doping amount of Dy₂O₃ doped CeO₂-based electrolyte material is 5%,10%,15%,20%,25%and 30%,the crystal structure maintains the fluorite structure of CeO₂;The electrolyte powder is formed by pressure molding at 200 MPa,after sintering at 1450?for 5 hours in an air atmosphere,a dense electrolyte sheet was obtained.The grain size was observed to increase with increasing doping amount.When the doping amount x?20%,the grain size increases rapidly,which is about 4 times that of the doping amount of 5%?x?15%,and it is found by comparison with the literature that dysprosium oxide doped cerium oxide is more than gadolinium oxide doped cerium oxide in the growth of crystal grains.It is speculated that the addition of Dy₂O₃ contributes to the sintering of the electrolyte.The doping amount and oxygen vacancy concentration were studied by Raman spectroscopy.It was found that the oxygen vacancy concentration and DyO₈ defect concentration were proportional to the doping amount,and the oxygen vacancy concentration increased faster than the DyO₈ concentration with the increase of doping amount.Electrochemical performance studies have found that the conductivity increases first and then decreases with the increase of doping content.When the doping amount is 25%,the conductivity is maximum at 4.80×10^-22 S·cm^-1 at 750?.The activation energy is 0.91 eV.The electronic conductivity of Dy₂O₃ doped CeO₂ based electrolyte materials is relatively large.When the doping amount is 20%,the electronic conductivity is minimum at 4.63×10^-3 S·cm^-1.The Sc₂O₃ doped CeO₂-based electrolyte material has a maximum solid solubility of 5%due to the large difference in ionic radius.When the doping amount continues to increase,black precipitate will form,and with temperature increased the precipitation increased.The conductivity test results of Sc₂O₃ doped CeO₂ electrolyte show that the electrolyte conductivity is low in the range of Sc₂O₃ doping amount studied in this paper.The conductivity of CeO₂electrolyte with 8%mol Sc₂O₃ doping at 1500?is the highest.The conductivity of the electrolyte at 750?was 8.78×10^-3 S·cm^-1 and the activation energy was 1.220 eV.The Dy₂O₃ and Sc₂O₃ co-doped CeO₂-based electrolyte materials Ce_0.75Sc_xDy_0.25-xO_1.875?x=0.03,0.04,0.05 and 0.06?maintained a good CeO₂ fluorite structure in the doping amount range.When the surface morphology was observed,the co-doping was more favorable than the single doping,and the average grain size decreased with the increase of Sc₂O₃ content.When studying the relationship between the oxygen vacancy concentration and the doping amount of the co-doped electrolyte,it is found that the co-doping has a higher oxygen vacancy concentration than the single-doping.The vacancy concentration is the highest when the doping amount of Sc₂O₃ is 4%and the Dy₂O₃ is 21%.Electrochemical performance studies have found that co-doping has higher electrical conductivity and lower electronic conductivity than single doping.The conductivity at 750?is 9.39×10^-2 S·cm^-1,the activation energy is 0.80 eV and the electronic conductance is 9.15×10^-4 S·cm^-1 when the amount of Sc₂O₃ is 4%and the Dy₂O₃doping amount is 21%.The thermal conductivity of Ce_0.75Sc_0.04Dy_0.21O_1.875 electrolyte with the highest conductivity has good thermal compatibility with the electrode material and created good conditions for battery assemble.