Preparation Of GDC Composite TiO₂/MgO And Study On Grain Boundary Scavenging Effect

As an energy production device,solid oxide fuel cell（SOFC）can effectively convert chemical energy into electrical energy,and has great development prospects.The electrolyte,one of its main components,has an important impact on the temperature and operation of the battery.For electrolyte materials with different conductivity between grain and grain boundary,the conductivity of grain boundary is usually affected by two main factors:space charge potential and grain boundary impurity coverage.In the process of material preparation,no matter what preparation method is adopted,some Si impurities will inevitably be produced.Therefore,reducing the coverage of grain boundary impurities is the main way to improve the grain boundary conductivity of samples.The common method of removing grain boundary impurities is cation doping,but in the relevant reports,the research on cation doping related to electrolyte does not systematically explain the variation law of grain boundary conductivity and grain boundary scavenging effect.In this paper,CeO₂,a traditional electrolyte material with simple preparation process and high conductivity,was selected as the matrix material,and transition metal oxide（TiO₂）and alkaline metal oxide（Mg O）were added respectively.GDC-Mg O and GDC-TiO₂series samples were prepared by self propagating combustion method.The sintering temperature of the samples was changed to make them above and below the eutectic temperature.According to the change of electrochemical impedance data of each sample,the electrical properties and grain boundary scavenging effect of the material are studied.The results show that the XRD spectra show that the diffraction peaks of all samples are consistent with the standard card,and no other heterophase peaks are observed,indicating that the samples are cubic fluorite structure.It can be seen from the SEM photos of the surface that the structure of all samples is dense,and the grain boundary grains are clearly visible and evenly distributed.This study shows that when the sintering temperature of the sample is higher than the eutectic temperature of impurities（Si）in the grain boundary,the added additives(Mg²⁺,Ti⁴⁺)can form eutectic compounds with impurities（Si）in the sintering process,and move these eutectic compounds to a specific area during the cooling process,so as to complete the impurity scavenging and realize the grain boundary scavenging effect.After in-depth investigation of a large number of reports on the effect of grain boundary additives on grain boundary conductivity,this study comprehensively expounds the mechanism of grain boundary impurity scavenging effect with transition metal oxides and alkaline metal oxides as additives respectively.