Preparation Of Multiple-doping Of Apatite-type Lanthanum Silicate Solid Electrolyte By Combustion Process

Solid oxide fuel cell?SOFC?has broad application prospects in the global energy market,so it has important practical significance for the development and research of its core components solid electrolyte.Today,high performance electrolyte materials are no longer limited to traditional fluorite-type electrolytes and perovskite electrolytes.Apatite-type silicate-based electrolyte materials?LASMO?have high electrical conductivity in the mid-temperature range?500-800??.And there is almost no electronic conductance in a wide range of oxygen partial pressures.It has become one of the most promising high performance electrolyte materials.In this thesis,the process conditions of multi-doping of LASMO electrolyte materials by combustion method were studied,and the mechanism of multi-position doping to enhance the conductivity was discussed.The details are as follows:Firstly,multi-doped LASMO electrolyte powders were synthesized by urea-nitrate combustion method,and the phase structure analysis was carried out.The calcined electrolyte powder has high crystallinity and a complete p6₃/m apatite crystal structure,and the multi-site doping does not significantly change the phase structure of the electrolyte powder.The average grain size of La_9.33Ca_xSi_6-yZn_yO_25+xis calculated to be 29.2 nm,the average grain size of La_9.33Sr_xSi_6-yZn_yO_25+xis 30.5 nm,and the average grain size of La_9.33Ba_xSi_6-yZn_yO_25+xis 32.2 nm.It is indicated that the grain size of the LASMO electrolyte powder prepared by the combustion method is in the nanometer range,which is beneficial to the sintering of the electrolyte sheet.Secondly,LASMO electrolyte sheets were prepared by sintering method.The effects of sintering temperature and doping content on the morphology and electrical properties of LASMO electrolytes were studied.The optimum process parameters of multi-doping were obtained.The optimum sintering temperature of Ca,Zn multi-doped La_9.33Ca_xSi_6-yZn_yO_25+xelectrolyte is 1500°C.The La_9.33Ca_xSi_6-yZn_yO_25+xelectrolyte has high density when Ca doping amount is x=0.2 and Zn doping amount is y=1.0.Its conductivity can reach3.58×10^-3S/cm at the test temperature of 800?.The optimum sintering temperature of Sr,Zn multi-doped La_9.33Sr_xSi_6-yZn_yO_25+xelectrolyte is 1400°C.The La_9.33Sr_xSi_6-yZn_yO_25+xelectrolyte has high density when Sr doping amount is x=0.2 and Zn doping amount is y=1.0.Its conductivity can reach 5.43×10^-3S/cm at the test temperature of 800?.The optimum sintering temperature of Ba,Zn multi-doped La_9.33Ba_xSi_6-yZn_yO_25+xelectrolyte is1400°C.The La_9.33Ba_xSi_6-yZn_yO_25+xelectrolyte has high density when Ba doping amount is x=0.2 and Zn doping amount is y=1.0.Its conductivity can reach 2.34×10^-2S/cm at the test temperature of 800?.Finally,the chemical composition of multi-doped LASMO electrolyte was characterized by XPS.The results show that the full spectrum of XPS before and after doping is well correlated,and the doping of polyposition does not significantly change the chemical structure of the electrolyte.At the same time,the relationship between conductivity and test temperature of multi-doped LASMO electrolytes is in accordance with the Arrehenius formula,indicating that the multi-doped LASMO electrolyte has good stability.The LASMO electrolyte conductance mechanism belongs to the interstitial oxygen conduction mechanism.The proper amount of ion doping can increase the amount of interstitial oxygen in the electrolyte crystal structure,thereby increasing the conductivity of the electrolyte.