Preparation Of Transition Elements Doped Lanthanum Silicate Oxyapatite Electrolyte By Combustion Process

Apatite-type lanthanum silicate electrolyte is expected to be widely used in solid oxide fuel cells because of its high ionic conductivity and low activation energy at low temperatures.Therefore,the research on the ionic conductivity around the apatite-type lanthanum silicate electrolyte has been gradually enriched in recent years.The results show that the key to improve the electrical conductivity of LSO lies in two points:?1?reasonable preparation processes and?2?the researches about doping modification.Apatite type lanthanum silicate electrolyte as an excellent low temperature electrolyte material,its conductivity is closely related to composition phase and microstructure of electrolyte sintered body.Reasonable discussion of the influence of each process on the structure and properties of the electrolyte shows great significance for the preparation of electrolytic materials with excellent conductivity.Based on the as-synthesized La_9.33?SiO₄?₆O₂ electrolyte with best technological parameters,the doped electrolytes with suitable dopant were also discussed.The doping of metal ions were not only improve conductivity of electrolyte,but also keep the previous crystal structures well,which are the development trend in the research of electrolyte materials.Therefore,this paper explores the best preparation parameters of La_9.33?SiO₄?₆O₂ electrolyte by structural characterization and performance analysis to obtain LSO electrolyte with excellent conductivity.On the other hand,synthesize the LSMO electrolyte LSMO by doping transition metal ions into the lattice of LSO to improve the conductivity of LSO electrolyte.In this experiment,the preparation parameters such as ball milling time of La_9.33?SiO₄?₆O₂ powder,the preforming pressure of La_9.33?SiO₄?₆O₂ billet and the sintering system of La_9.33?SiO₄?₆O₂ electrolyte were studied by XRD,SEM and density analysis,and the optimum preparation process was obtained.The chemical structure and conductivity of the as-prepared La_9.33?SiO₄?₆O₂ electrolyte under the optimum preparation conditions were analyzed by XPS and AC impedance method.The as-prepared La_9.33?SiO₄?₆O₂ electrolyte has good chemical structure,the full-scale XPS spectrum suggest the characteristic peaks is obvious and does not contain other impurity elements,and the conductivity of as-synthesized electrolyte at800 ^oC up to 1.71×10^-3 S·cm^-1.In this study,Cu element was used to dope into LSO electrolyte.The optimum doping materials was determined by analyzing the phase and element distribution of as-prepared electrolyte with different dopant materials.The optimum doping content was determined by XRD,SEM and conductivity analysis of La_9.33Si_6-xCu_xO_26-x electrolyte with different doping content.The total conductivity of as-prepared La_9.33Si_6-xCu_xO_26-x at best process condition is 7.28×10^-3 S·cm^-1 at 800 ^oC.In this experiment,La_9.33Si_6-xZn_xO_26-x electrolyte was successfully prepared by using ZnO as the dopant raw material.Firstly,the influence of different doping content on the lattice of LSO was analyzed by XRD.Secondly,the change of crystallinity during the formation of La_9.33Si_6-xZn_xO_26-x powder was analyzed by TEM,and the change of LSO microstructure because of the doping of Zn was analyzed by SEM.Finally,the conductivity of the La_9.33Si_6-xZn_xO_26-x electrolytes with different doping contents was tested by using the AC impedance method to determine the optimum doping content.The XPS analysis suggests as-synthesized La_9.33Si_6-xZn_xO_26-x electrolyte with the best doping content possesses a good chemical structure,and the Zn-Si-O bond can be detected in the spectrum.The conductivity of as-synthesized La_9.33Si_6-xZn_xO_26-x electrolyte is about 2.11×10^-2S·cm^-1 at 800 ^oC.In this experiment,Fe,Co and Ni doped apatite lanthanum silicate electrolytes were prepared respectively.The phase structure and microstructure of La_9.33Si₅FeO₂₅,La_9.33Si₅CoO₂₅ and La_9.33Si₅NiO₂₅ electrolyte were compared.Comparing with La_9.33?SiO₄?₆O₂ electrolyte,the relative densities of the Fe-doped,Co-doped and Ni-doped LSO electrolytes were obviously decrease,which were mainly caused by the oxidation of metal ions during the sintering process.Finally,the electrical properties of five transition elements doped LSO electrolytes were compared.The improving mechanism of the conductivity in transition eleents doped LSO was been discussed.Among them,La_9.33Si₅ZnO₂₅electrolyte possesses the best conductivity.