Prearatiopn And Performance Of Intermediate-temperature Solid Oxide Fuel Cell Cathode Materials By Sol-gel Method

As one of energy conversion devices, Solid Oxide Fuel Cell(SOFC) had got too muchattention due to their advantages in terms of being solid state, with no electrolyte corrosion,and high efficiency. Intermediate-low temperature SOFC could better avoid the harmfuleffects by the reactions between electrolyte and electrode material. So SOFC can be used in along term.This paper is based on the synthesis of the intermediate-temperature solid oxide fuel cellcathode materials La0.7Sr0.3Fe0.8Co0.2O3(LSFC)powder. Dsicussing the effect on the powderby each process condition of the sol-gel method of modified PVA, we got the optimalexperimental conditions:when pH=7, the mass rate of the PVA and nitrate was1:5, and themolar ratio of citric acid to metal ion be1.5:1, it could be formed the transparent, clear, andthe well conformation of sol. The sol changed the gel after12h, the gel was made of LSFCprecursors at the155℃in oven. The LSFCprecursors, which was calcined at900℃for2h,has formed the powder with the single and stable perovskite structure and the diameterdistributing uniformity.A series cathode materials such as La0.7Sr0.3-xCaxFe0.8Co0.2O3(LSCFC，x=0.1，0.15，0.2)and La0.7Ba0.15E0.15Fe0.8Co0.2O3(LBEFC，E=Sr，Ca)could be preparation by the sol-gelmethod of modified PVA.The research showed that LSCFC powder could formed a singlephase perovskite structure when it was calcined at900℃for2hours. Double doped by A andB sites of LSCFC induced LaFeO3cell volume expanding. The expansion ratio ofLa0.7Sr0.15Ca0.15Fe0.8Co0.2O3is43.3%. The espasion ratio of LSCFC become smaller when thedoping content of small radius Ca2+was increased. LBEFC powder could be also formed asingle phase perovskite structure when it was at1000℃for2hours. The cell volume ofLBEFC changed when the larger radius Ba2+was doped. The expansion ratio of LBSFC andLBCFC are43.5%and42.7%. Between300-800℃, the electrical conductivities of the seriescathode materials such as LSCFC and LBEFC changed according with the adiabatic-hoppingof p-type small polarons. Their electronic transport behavior in low temperatureregion(300-480℃) is attributable to the small polaron hopping mechanism, and charge compensation of oxygen vacancies mechanism at high temperatures. At hightemperature(480-800℃), the conductive type undergo semiconductor to metal transitions.Besides, Ca2+induced the electrical activation energy, So the the electrical conductivitities ofLSCFC become smaller when the doping content of Ca2+was increased. The electricalconductivities of LBSFC is larger than LBCFC’s. Being doped by Ba2+is good for enhancingthe oxygen vacancies of crystal structure, decreasing the small polaron concentration of thesystem. That’s why the electrical conductivitities of LBEFC is smaller than LSCFC’s.Electrolyte materal Ce0.8M0.2O2-δ(CMO，M=Sm，La，Sr) was prepared by sol-gel method.By the analysis of XRD diagram of CMO, we got that the difficulty level is closely related tothe ion’s radius. The difficultity level of the followings are Ce0.8Sm0.2O2-δ＜Ce0.8La0.2O2-δ＜Ce0.8Sr0.2O2-δ. Sm3+has the smallest radius, so it can easily enter ceria latrtice, and formed astable fluorite-structure at800℃for2hours. So doesLa3+at900℃for2hours.Sr2+withlarger radius, formed an incomplete fluorite-structure at800℃. An impure peak appeared at29.64°. Raising temperature till900℃, there is still impure peak. It maybe indicated that Sr orits oxides precipitated. In addition, there is a study on the conductivity properties of CLO,which has150times of electrical conductivities than pure CeO2. The electrical conductivitiesof CLO can be0.049S/cm, and electrical activation energy be84.48kJ/mol.