The Effect Of Single/double Sintering Aids On The Structure And Properties Of Nd_0.2Ce_0.8O_1.9 Electrolyte

The solid oxide fuel cell（SOFC）consists of three parts:cathode,anode,and electrolyte.It is worth noting that the dense electrolyte between the fuel gas and the oxygen acts as an intermediate barrier layer,eliminating the explosion.In addition,the dense electrolyte ensures the rapid transport of oxygen ions through grain boundaries,resulting in the high ionic conductivity.At medium and low temperature（<800℃）,the Ce O₂-based electrolyte achieves excellent ionic conductivity and good compatibility with commonly used electrode materials.However,Ce O₂-based electrolyte exhibits two major shortcomings:one is the introduction of electronic conductivity due to partial reduction of Ce⁴⁺to Ce³⁺at reducing atmospheres or at high temperatures;another is that the density is difficult below 1400℃.The high operating temperatures create many new challenges,e.g.,the increase of the aging rate,the decrease of the long-term stability,as well as the poor compatibility with the cell components.Addition of metal oxide（<5wt%）,has been extensively investigated as sintering aids to improve the sintering ability and electrical property of Ce O₂-based electrolytes.Using dual-sintering additives,high density ceramics were obtained at reduced temperature,and better electrical performance and microstructure than that using single sintering aid.In this paper,Nd₂O₃-doped Ce O₂（NDC）used as the research system,to study the effects of salt single sintering additives and double sintering additives.We systematically studied the 1-5 wt%Bi VO₄ and different mass ratio of Bi₂O₃/ZnO on the structure and electrical properties to ensure the optimal addition amount and ratio to improve the density and conductivity of NDC electrolytes.Bi VO₄（BV）,Nd_0.2Ce_0.8O_1.9（NDC）and NDC-based electrolyte powders were prepared by the sol-gel method.The prepared samples were analyzed by X-ray diffraction（XRD）,field emission scanning electron microscopy（FE-SEM）for phase analysis and microscopic morphology observation.Then the Ac impedance spectrum of samples was characterized by electrochemical workstation.（1）Adding BV as a sintering aid to the NDC samples,the sintering temperature reduced from 1400℃to 1200°C.By observing the cross-sectional morphology by SEM and calculating the corresponding shrinkage rate.BV acts as a sintering aid and promotes the densification process of the electrolyte.At 700°C,the total conductivity is 3.35×10^-2 S?cm^-1,the polarization resistance decreases more than 34%,and the maximum power density reaches 514 m W?cm^-2.The open-circuit voltage of the cell maintained a good long-term stability after 70 h.（2）Using"Bi₂O₃+ZnO"（Bi/Zn）as double sintering aid,"Bi₂O₃+ZnO"showed better effect than Bi₂O₃ or ZnO single sintering aid,and the conductivity and density of 3Bi/1Zn-NDC were significantly improved.The total conductivity of 3Bi/1Zn-NDC is 5.89×10^-2 S?cm^-1 at 700℃,which is 4.60 and 4.51 times that of 4Bi-NDC and 4Zn-NDC.The single cell was assembled by 3Bi/1Zn-NDC electrolyte,its open-circuit voltage is 0.67 V and the maximum power density reaches 402.25 m W?cm^-2 at 700°C.The single cell maintains excellent power output and stable open-circuit voltage during the long-term stability test of50 h.Both Bi VO₄ and Bi₂O₃/ZnO can effectively reduce the sintering temperature and increase the density of NDC electrolytes.They are good sintering aids and can significantly improve the electrical properties of NDC electrolytes.