Preparation And Performance Of Ce_1-xRe_xO_2-δ(Re=Sm, Gd) Based Composite Electrolyte Materials For IT-SOFCs

A fuel cell is a kind of energy conversion device which has advantages of higher energy conversion efficiency than traditional generator and are also friendly to environment. The fuel cell is composed of cathode, anode and electrolyte. Solid oxide fuel cell (SOFC) is a fuel cell with whole solid structure and its comprehensive utilization of energy can reach 80%. SOFC can use a l large of different fuels ,from H2, CO to natural gas, liquefied gas and other hydrocarbons. The main difficulty the SOFC faces currently is the problem caused by high temperature and the ceramic components'match.SOFC electrolyte is the core of the battery, whose performance has a direct impact on the overall performance of the battery. The electrolyte has to meet the following requirements: a high oxygen ion conductivity; low electronic conductivity; resistance to reactive gas. SOFC generally employs the traditional yttria stabilized zirconia (YSZ) as electrolyte, but this type of electrolyte for SOFC is required to work at 1000℃. Such a high operating temperature of the battery has already put forward various strict requirements for SOFC, which will bring a series of questions. Therefore, it is extremely important to reduce the operating temperature of SOFCs. On the one hand, we can make the electrolyte of YSZ into thin films to reduce the battery's internal resistance and finally improve the battery performance. On the other hand, we may look for new electrolyte materials that can work in intermediate- temperature range, below 800℃.Due to the high cost and complicated process of the films technology, the former proposal is restricted. CeO2-doped electrolyte is one of the most attractive material for IT-SOFC electrolyte. But its mechanical strength is low, moreover this material has a degree of electrical conductivity, which reduces the output performance of fuel cells. Therefore, CeO2-doped electrolyte is difficult to realize its industrial production. It is known that composite materials can not only be designed and produced according to the needed requirements, but also show a comprehensive advantage of all raw materials. In this paper, we did a detailed research on the Re-doped CeO2 (Re = Sm, Gd). And we synthesized Ce_1-xRe_xO_2-δ (Re = Sm, Gd) and LSGM composite electrolyte materials. We made a full advantage of the two kinds of electrolyte materials, and overcome the shortcomings of a single electrolyte.The electrolyte materials Ce_0.85Sm_0.15O_1.925(SDC),Ce_0.9Gd_0.1O_1.95 (GDC) and La0.9Sr0.1Ga0.8Mg0.2O3-δ(LSGM) were synthesized by means of glycine-nitrate process(GNP) and then the SDC-LSGM and GDC-LSGM composite electrolyte were prepared by solid-state method(the weight ratio between Ce_1-xRe_xO_2-δ powder and LSGM powder were 95∶0 5,90∶10,85∶15, respectively). We studyed the structure and properties of composite electrolytes in the present work. SOFC were fabricated with Ni_0.9Cu_0.1-SDC as anode and BaCo_0.7Fe_0.22Nb_0.08O_3-δ as cathode, The results showed that a small amount of LSGM can promoted grain growth. But the composite electrolytes with ratio of 85:15 has a few microporous, which will become an obstacle for oxygen ion conduction. The conductivity tests also showed poor performance. When a small amount of LSGM is composited, the boundary resistance can reduced, which is helpful to improve the total conductivity of samples. Among all the SDC-LSGM and GDC-LSGM composite electrolyte materials, the one with ratio of 95:05 showed the best performence. Single-cell tests showed that the output performance of the cells which employed the composite electrolyte are much better than cells with pure SDC or GDC.Among the SDC-LSGM composite electrolyte, the one with ratio of 95:05 showed the maximum power output density 0.484W / cm2 at 800℃. While among the GDC-LSGM composite electrolyte, the one with ratio of 95:05 showed the maximum power output density 0.477W/cm2 at 800℃.SDC-CoO composite electrolyte materials were prepared to study the structure and properties of composite electrolytes. SOFC were fabricated with Ni_0.9Cu_0.1-SDC as anode and BaCo_0.7Fe_0.22Nb_0.08O_3-δ as cathode. The results showed that cubic fluorite phase unit cell parameters of SDC-CoO composite electrolyte are basically unchanged under different sintering temperature. CoO can promoted grain growth. Especially for the SDC-CoO composite electrolyte sintered at 1400℃, the increment of grain size are very significant, which reduced the grain boundary resistance and enhance the conductivity. The conductivity of SDC-CoO composite electrolyte sintered at 1400℃is greater than the that of SDC sintered at the same temperature. While the conductivity of SDC-CoO composite electrolyte sintered at 1250℃is worse than that of SDC sintered at the same temperature. Single-cell tests showed that the power density of the cell, which employed SDC-CoO as composite electrolyte under 1400℃sintering temperature, is higher than the cell using SDC as electrolyte. The maximum power output density was 0.503W/cm2 tested at 800 oC for the cell with SDC+1mol%Co sintered at 1400℃as electrolyte.