| Solid oxide fuel cell (SOFC) has been considered as a hot topic in the fuel cell research field because of its efficient, clean, safe and reliable, at the same time, it has high power density, solid-state structure, a wide range of fuel and little environmental pollution, etc. ZrO2-based electrolyte materials have been considered as the most promising electrolyte materials of SOFC for its high ionic conductivity and lower activation energy of conductivity. However, high sintering temperatures of over1600℃are required for ZrO2-based electrolyte to obtain a higher density, which not only increases the electrolyte material preparation costs, while accelerating degradation of the fuel cell system, and therefore under a lower sintering temperature to obtain higher density of ZrO3-based electrolyte materials that has become the focus of the study. In recent years, MoO3has caused widespread interest in the study for its unique layered structure, low solubility in organic solvents and low degree of polarization. Studies have shown that small amounts of transition metal oxides MoO3added to Nd2O3doped CeO2or Gd2O3system, not only has the role of sintering additives, and also has the role of grain boundary scavenge. However, with regard to MoO3-doped Zr0.84Y0.16O1.92system (hereinafter referred to as8YSZ system), whether it can be used as sintering aids, and the best amount of MoO3-doped and sintering temperature is very rarely been reported. In this paper, using the MoO3-doped8YSZ system for the study, we discussed the influence on the system structure and electrical properties of the different sintering temperatures and different amount of MoO3-doped8YSZ, confirmed MoO3-doped8YSZ system playing the role of sintering aids, and further determined the optimal sintering temperature and the best amount of MoO3-doping.The main research contents of this paper are as follows:The high pure (SiO2<50mg/kg) Zr0.844Y0.16O1.92(8YSZ) solid solution was prepared by the so-gel method. In its base, preparing the8YSZ+xMoO3(0.00≤x≤0.07) system. Their structures and ionic conductivities were characterized by X-ray Diffraction (XRD), Field-emission Scanning Electron Microscopy (FE-SEM) and Electrochemical Impedance Spectroscopy (EIS). Using0.05%MoO3-doped8YSZ system for the study, sintered at1350℃,1450℃and1550℃for20h, then it was discussed that the effects of different sintering temperature on the structures and conductivity of the system to determine the optimal sintering temperature; further, using8YSZ+xMoO3(x=0.00,0.01,0.03,0.05,0.07) system for the study, sintered at1350℃,1450℃and155O℃respectively for20h, then it was discussed that the effects of the different amount of MoO3-doped on the structures and conductivity of the system to determine the optimal doping amount of MoO3, and to determine whether MoO3can play the role of sintering additives. The results showed that:(1) In high-purity8YSZ system, the optimal sintering temperature of MoO3-doped is1450℃. MoO3-doped8YSZ system remains cubic fluorite-type structure; MoO3-doped8YSZ system can improve the density and grain size, while significantly increase the boundary conductivity and total conductivity of the system;1350～1450℃is the sintering active zone,1450～1550℃is the sintering terminable zone. MoO3-doped8YSZ solid electrolyte system can lower sintering temperature, increase density and promote the grain boundary movement; it has played the role of sintering additives.(2) In high-purity8YSZ system, the optimal doping amount of MoO3is0.05mol%. The grain and density of MoO3-doped samples are increased, then they reach the maximum at the doping of0.05mol%; MoO3doping can reduce the sintering temperature, promote grain growth and improve the system density, this is because the lower melting point of MoO3(795℃), it melts to the liquid phase in sintering process, play the role of lubricant between grains, while under the influence of the grain surface tension, making the location change between the grains and their contacts to speed up the grain boundary mobility, making the connection between the grains more closely, thereby enhancing the sintering rate, prompting the sample grain size and density increase. At different sintering temperatures, MoO3-doped system increases the total volume conductivity, electrical conductivity and grain boundary conductivity. |
PDF Full Text Request