Preparation And Performance Of CeO₂ Based Electrolyte Composite Transition Metal Oxides (CoO, MgO) For SOFCs

A fuel cell is a kind of energy conversion device which can convert the chemical energy stored in the fuel and oxidizer into electricity directly. The conversion is efficient and friendly to environment. The fuel cell is composed of cathode, anode and electrolyte. It has advantages of higher energy conversion efficiency and lower pollution to environment. Solid oxide fuel cell (SOFC) is a fuel cell with all solid components and its comprehensive utilization of energy can reach 80%. SOFC can use a large of different fuels, from hydrogen, carbon monoxide to natural gas, liquefied gas and other combustive gases.Solid electrolyte is the most core components in the SOFC, whose performance not only affect the operating temperature and conversion efficiency, but also decide the electrode materials matching with electrolyte and the choice of preparation technology. The requirements of electrolyte are: high oxygen ionic conductivity; low electronic conductivity; resistance to reactive gas. Solid oxide fuel cells use the traditional yttria stabilized zirconia (YSZ) as electrolyte and it has a sufficiently high ionic conductivity at temperatures higher than 1000℃. The high temperature may cause serious problems for sealing materials, thermal mismatches and reaction between interface materials, leading to higher manufacturing cost and application limitation. If we reduce the operating temperature of the fuel cells to 800℃, then we can avoid a series of problems which caused by working in high temperature. The doped ceria electrolyte has a higher ionic conductivity than the traditional YSZ electrolyte operating at 600-800℃, which is considered a promising electrolyte materials for intermediate temperature solid oxide fuel cell (IT-SOFC). The doped ceria electrolyte is the most attractive IT-SOFC electrolyte material. Its mechanical strength is low and the electronic conductivity has reduced the output performance of fuel cells. 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 doped ceria electrolyte. And we prepared transition metal oxides (CoO or MgO) and doped ceria electrolyte composite electrolyte materials, in order to reduce the sintering temperature and increase the conductivity.We prepared 1mol%CoO and Ce_0.9Gd_0.1O_1.95(C℃GO) composite electrolyte materials by means of glycine-nitrate process. Then we prepared Ce_0.9Gd_0.1O_1.95(CGO) electrolyte materials by the same process. They have different structure and properties at different sintering temperature. SOFCs were fabricated with Ni_0.9Cu_0.1-CSO as anode and BaCo₍0.70Fe_0.2Nb_0.1O_3-δ as cathode. Then we analysed the output performance of the single battery. Conductivity test showed that the total conductivity of CGO is larger than C℃GO sintered at 1400℃. The electrolyte material C℃GO sintered at 1200℃showed the highest total conductance, and it is higher than CGO sintered at 1400℃. Single-cell tests showed that the power density of the cell, which employed C℃GO as composite electrolyte, increased with the sintering temperature of the C℃GO electrolyte. The electrolyte material C℃GO sintered at 1200℃showed the maximum power output density 480mW/cm2 at 800℃. The power density of the cell, which employed C℃GO sintered at 1200℃and 1300℃as composite electrolyte were higher than the cell employing CGO sintered at 1200℃as electrolyte. The results show that 1mol%CoO could reduce the sintering temperature of the CGO electrolyte.We prepared transition metal oxide MgO and Ce_0.9Gd_0.1O_1.95(CGO+xMgO) composite electrolyte materials by means of glycine-nitrate process. The electrolyte materials CGO+xMgO have different structure and properties with different proportions of MgO. SOFCs were fabricated with Ni_0.9Cu_0.1-CSO as anode and BaCo_0.7Fe_0.2Nb_0.1O_3-δ as cathode. Then we analysed the output performance of the single battery. Conductivity test showed that the total conductivity of CGO+1MgO than CGO sintered at 1400℃. The total conductivity of the other composite electrolyte is slightly lower than the CGO sintered at 1400℃. Single-cell tests showed that the maximum power density of the cell, which employed CGO+1MgO as composite electrolyte, is 439mW/cm² at 800℃. As the MgO content increased, the output performance of cells decreased.The electrolyte materials of transition metal oxides MgO and Ce_0.85Sm_0.15O_1.925 (CSO+xMgO) composite electrolyte materials was prepared by glycine-nitrate process, and the impacts of the different ratios of MgO on the composite structure and properties of the electrolyte were investigated. With Ni_0.9Cu_0.1-CSO as the anode, BaCo_0.7Fe_0.2Nb_0.1O_3-δ as cathode, composite different proportions MgO of the CSO as the substrates the cell was fabricated, and its output performance was tested. Electrical conductivity tests show that, the total conductivity of CSO+1MgO composite electrolyte sintered at 1400℃were almost the same,the other composite electrolytes' were all improved. Single-cell tests showed that the maximum power density of the cell, which employed CGO+1MgO as composite electrolyte, is 534mW/cm² at 800℃. As the MgO content increased, the output performance of cells decreased.