Nano Ceo <sub> 2 </ Sub> Preparation And Properties Of Solid Electrolytes

Solid oxide fuel cells (SOFCs) are known as a kind of clean, pollution-free, high-efficientcy energy system in the 21st century. Solid oxide electrolyte (oxygen ion conductor) is a key component in SOFCs. The solid electrolytes based on CeO2 are a type of potential solid electrolyte materials at intermediate temperatures because of its higher oxide-ion conductivity compared to those of solid electrolytes based on ZrO2. However, there remain some flaws for CeO2 electrolyte materials, which would limit its commercial application. For example, the synthesized process of CeO2 electrolyte is complicated; the sintering temperature is too high to form a high quality ceramic pellet, In addition, the oxide-ion conductivity of CeO2 electrolytes decrease at intermediate and low temperature regimes. Therefore, CeO2 electrolytes with better electrical performance and simply prepared process are necessary to be developed. In this thesis, ther research work is focused on the followings:Ce1-xLnxO2-δ(Ln=Pr, Nd, Sm, Gd) (x=0.05～0.25) nanosized mateials are synthesized by a composite-hydroxide mediated (CHM) method. The samples are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD patterns indicate that the products have cubic ceria structures. TEM images show that Ce1-x(Nd/Pr)xO2-δand Ce1-x(Sm/Gd)xO2-δsamples are composed of nano-spindles and nanoparticles, respectively. The relative density of species sintered at 1350-1400℃is about 80%. The electrochemical properties of these materials are preformed by EIS technique. The results suggest that Ce0.80Nd0.20O2-δhas a higher conductivity of 4.1×10-2 S cm-1 at 800℃in air, and the activation energy is 0.83 eV.In order to improve the density and electrical performance of Ce1-xLnxO2-δ(Ln=Pr, Nd) materials, we prepare a serials of Ce1-x-yLnxCoyO2-δ(Ln=Pr, Nd) nanosized electrolyte materials using the similar method, and investigate the characterizations and properties of the products. The as-preparfed Ce1-x-yPrxCoyO2-δand Ce1-x-yNdxCoyO2-δsamples consist of nanorods and nanoparticles, respectively. The relative density of specie can reach about 90% after sintering at 1400℃. Ce0.78Nd0.2Co0.02O2-δhas a conductivity of 0.1 S cm-1 at 800℃. The CeO2 nanosized electrolytes doped by lanthanide-transition metals have the higher conductivity and lower activation energy compared to those of lanthanide-doped CeO2 nanosized electrolytes.