Study On The Electrical Properties Of Bi₂O₃ Composite Oxygen Ion Conductors

Solid oxide fuel cell?SOFC?is characterized by the use of ceramic electrolyte materials,an all-solid structure.The key to the improvement of SOFC performance lies in the development and research of electrolyte materials.Currently,the electrolyte materials of SOFC are mainly divided into cerium oxide base,bismuth oxide base,perovskite structure electrolyte,etc.Among them,the fluorite structure bismuth oxide base electrolyte material has many advantages,while the Bi₂O₃ electrolyte material can present different crystal structures at different temperatures and conditions,thus affecting its performance improvement.In order to obtain the best performance and better stability of Bi₂O₃ oxygen ion conductor electrolyte materials,the research work of this paper mainly focuses on the following aspects:In this paper,the delta phase of Bi₂O₃ was stabilized by a double doping system,and the oxygen ion conductor electrolyte materials with Er and Yb,Y and Zr co-doped Bi₂O₃ were prepared by glycine-nitrate method.The properties of the samples were characterized by means of X-ray diffraction?XRD?and scanning electron microscopy?SEM?.The phase analysis by XRD showed that all the ceramic electrolyte samples had good single-phase cubic fluorite structure,and no other heterofacies peaks were observed in the XRD pattern.When the sintering temperature of the sample is 800?,the relative density of sample Bi_0.76Y_0.18Zr_0.06O_1.5+?is about94.2%.Moreover,the electrochemical properties of the material were tested.The results showed that the Bi_0.76Y_0.18Zr_0.06O_1.5+?electrolyte material had a high conductivity,which reached 0.1421scm^-1 and 0.62eV in an atmosphere of 750?.In order to further improve the density and electrical properties of doped Bi₂O₃oxygen ion conductor electrolyte materials,solid phase sintering method was used to prepare the electrolyte materials that were co-doped with Bi₂O₃ by Zr,Lu,Lu and Ti respectively.The experimental results show that the electrolyte materials obtained by Zr and Lu co-doping Bi₂O₃ and Lu and Ti co-doping Bi₂O₃ can form good electrolyte thin sections after sintering at 800? for 5 hours.The microscopic morphology of all samples was observed by SEM,and the grain differentiation was obvious and the compactness was good,without obvious pore formation.Through the analysis of the conductivity test,the sample Bi_0.76Lu_0.16Ti_0.08O_1.5+?at 750? has the highest conductivity of 0.6843 scm^-1.However,due to the formation of a layer of fuzzy morphology on the surface of Zr and Lu co-doped Bi₂O₃ series samples,the relative density of sample Bi_0.76Lu_0.16Ti_0.08O_1.5+?reaches 95.2%.These results show that the delta-Bi₂O₃ phase is well stabilized after co-doping,and the electrolyte material has high ionic conductivity and low conductance activation energy,which improves its electrical performance and makes it a good oxygen ion conductor electrolyte material.