Infulence Of Metal Oxides-Dopant On Microstructure And Electrical Properties Of Purity NDC And Doped NDC Electrolytes

Solid electrolyte is an important part of Solid Oxide Fuel Cell (SOFC), which determine the operating temperature of the SOFC largely. CeO2 based electrolyte is one of the most promising electrolyte materials in intermediate temperature solid oxide fuel cells, which has higher ionic conductivity and lower conduction activation energy. But the main shortcomings of CeO2 based electrolyte is hard to densification under 1500℃, and high temperature sintering increases greatly the manufacture cost of CeO2 based electrolyte. Transition metal oxides as sintering additives can reduce the sintering temperature of the materials, and improves the conductivity of CeO2 based electrolyte. However many impurities Si phase will gather in the grain boundary of polycrystalline CeO2 based electrolyte materials, which has an adverse effect on the conductivity. Adding the grain boundary improver can promote the electrical conductivity of CeO2 based electrolyte materials. And the alkaline earth metal and rare earth metal co-doped CeO2 based electrolyte has high oxygen vacancy concentration, which can increase the number of conductive oxygen ions to increase the conductivity of the samples. Based on AeO (Ae=Mg、Ca and Sr) and Nd2O3 co-doped CeO2 as the research subject, we research the best doping ratio in the system and confirm the best doping system of alkaline earth metal. At the same time, we also research the addition of transitional metal oxides in the system of NMDC-Si and discuss the change of conductivity. The main research content of this paper are as follows:The high purity Ce0.8Nd0.2-xAexO1.9 (molar fraction, x) and the impurity Ce0.8Nd0.1-xAexO1.9+0.1(w) SiO2+xMOs (mass fraction, w) were synthesized by the sol-gel method. The characterizations focused on phase structure and electrical conductivity of all the samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). Electrical conductivity of the pellets was measured by AC impedance spectroscopy. The results demonstrated that:(1)The samples of Ce0.8Nd0.2-xMgxO2-δ (x= 0,0.05,0.10,0.15 and 0.20) present cubic fluorite structure. When x<0.10, there is no impurity phase; however, when x>0.10, there is impurity. The test of FE-SEM shows that adding a small amount of MgO will reduce the porosity of the samples and improve the density of the sample, effectively. But the content of MgO is too much, the increasing of porosity having no effect on the increasing of density, which is no conducive to the improvement of electrical conductivity. The sample of Ce0.8Nd0.1Mg0.1O2-δ has the smallest grain boundary resistance, total resistance and relative small total conductance activation energy, which make it have the largest electrical conductivity. The best doping amount of MgO is x=0.1 in the sample of Ce0.8Nd0.2-xMgxO2-δ, that is to say, the best proportion of Mg and Nd is 1:1.(2)The samples of Ce0.8Nd0.1Ae0.1O2-δ (Ae=Mg、Ca、Sr) present cubic fluorite structure and there is no other impurity phase. The test of FE-SEM shows that the addition of CaO results in the increasing of porosity and the decreasing of density, which lead to the lower conductivity; the addition of SrO results in promoting the growth of grain size contributing to the sintering of sample, but the distribution of grain size is nonuniform. The sample of Ce0.8Nd0.1Mg0.1O2-δ has the smallest grain boundary resistance, total resistance and relative small total conductance activation energy, which make it have the largest electrical conductivity.(3)The samples of Ce0.8Nd0.1Mg0.1O2-δ-Si+xMO present cubic fluorite structure. The test of FE-SEM shows that the addition of ZnO or Fe2O3 can promote the growth of grain and density, which make the sintering temperature decrease. The sample of Ce0.8Nd0.1Mg0.1O2-δ-Si has the smallest grain boundary conductivity and total conductivity. The addition of ZnO or Fe2O3 can remove or inhibit the impurity of silicon in the grain boundary, which can improve the grain boundary conductivity effectively, which can increase the total conductivity.