Effects Of MoO₃-dopant On Microstructure And Electrical Properties Of NDC/LSGM And Composite Electrolytes

Doped CeO₂-based polycrystalline electrolyte materials have higher ionic conductivities than YSZ does at low temperatures?500–700 ??and are considered to be the most promising medium low-temperature solid electrolytes.However,CeO₂-based electrolyte materials need to be sintered at a high temperature to obtain a higher density.While Ce⁴⁺ is easily reduced to Ce³⁺ in a reducing atmosphere or at high temperatures.Therefore,the application of CeO₂-based electrolyte materials is greatly limited.Increasing the sintering density of materials is an important means to optimize the structure and conductivity of CeO₂ electrolyte materials.The reduction in the grain size of the starting particles and the addition of sintering aids,such as Fe₂O₃?ZnO,CoO,CuO,and MoO₃ are effective ways to increase the density and thereby increasing the conductivity of the sample.On account of high ionic conductivity and ion transfer being almost independent of oxygen partial pressure,SrO-and MgO-codoped lanthanum gallate(La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8,LSGM)has become a promising medium and low temperature solid oxide fuel cell?IT-SOFC?electrolyte material.Owing to the complexity of cations in LSGM electrolyte,it is difficult to obtain pure LSGM samples at low sintering temperature?1500 ??.When some transition metal oxides[17] such as Mn₂O₅,CuO,V₂O₅,ZnO,CoO and Fe₂O₃ were added to LSGM respectively,the density,phase purity and ionic conductivity of LSGM had been improved.The combination of CeO₂ and LaGaO₃ electrolytes can overcome the shortcomings of the electronic conductivity of CeO₂-based materials and the poor stability of LaGaO₃-based materials.In addition,there is a lattice mismatch at the two-phase interface between the cubic fluorite structure of the CeO₂ and the perovskite structure of the LaGaO₃,which can produce many microstructure defects,the mobility of the oxygen vacancy in the dislocation-rich or high defect concentration regions is much higher than that in the ideal lattice.Therefore,the composite electrolytes show a higher total conductivity than that of single electrolytes.The addition of a small amount of MoO₃ in CeO₂-based electrolyte has the role of aiding sintering.Nevertheless,little information is available about adding MoO₃ to improve the sintering properties of LSGM and CeO₂-LaGaO₃-based composite electrolytes.The effects of the addition of MoO₃ on the microstructure and electrical conductivity of these different electrolyte systems were compared and discussed.The main research contents of this paper are as follows:?1?The Mo O₃ doped LSGM at 0-2.5 at.% respectively were prepared by an improved sol-gel method,the proper addition of MoO₃ can improve the phase purity of the LSGM samples.The complete crystalline structure formed temperature of LSGM-2Mo can be approximately reduced by 100 ? if the composition of the LSGM is slightly modified using 2 at.% of MoO₃.The sintering densification mechanism of LSGM samples was analyzed,and the relationship between the electrical properties of different samples and composition,structure were analyzed.The 2 at.% MoO₃-doped LSGM specimen exhibits highest phase purity,density,particle size and conductivity.MoO₃ is the ideal sintering additive for LSGM electrolyte.The optimum doping amount of MoO₃ is 2 at.%.?2?A small amount of MoO₃ was added in the NDC,LSGM and its composite system.By analyzing the XRD patterns and SEM images of the samples,it can be seen that the addition of MoO₃ contributes to the increase of the sample density and the growth of the sample particles,and MoO₃ has the effect of sintering auxiliaries.The grain,grain boundary and total conductivity of the MoO₃-doped electrolyte were significantly higher than those of the undoped MoO₃ electrolyte.The total conductivity at 450 ? of NDC-LSGM and NDC-LSGM-Mo were 0.87×10-3 and 1.01×10-3 S·cm-1,respectively,which are 1.81 and 2.10 times of the total conductivity of NDC.Therefore,doped MoO₃ NDC-LSGM composite samples have the highest total conductivity,is a potential alternative electrolyte materials of low-temperature solid oxide fuel cell.