The Electrical Properties Of Pr Doped LaGaO₃-based Electrolytes

SOFC attracts much attention in the whole world because of its advantagessuch as high efficiency, cleanness, no leakage and so on. Solid oxide electrolyte asthe SOFC core components is usually working at high temperature, resulting inseveral negative effects, such as electrode reaction, reduction of lifetime, etc. Inorder to reduce the operating temperature of SOFC, much investigation focus onmid-and low-tenperture electrolyte materials. It is reported that LaGaO₃-basedelectrolytes possess high conductivity at high temperature, while the activationenergy is also large. Compared to doped LaGaO₃, the activation energy ofPrGaO₃-based electrolytes is much smaller, which leads to higher electricalconductivity at reduced tenpertures. Therefore, the effect of Pr doping on theelectrical properties of LaGaO₃-based electrolytes are investigated, in order to findelectrolyte materials with superior performance at mid-and low-tempertures.In this paper, La_1-xPrxGa1-yMgyO₃electrolytes are successfully synthesized andcharacterized by X-ray diffraction, AC/DC electrical conductivity, thermalexpansion, and ion transport number. When the ratio of La and Pr is1:1, the highestelectrical conductivity is achieved at the Mg content of15%(La_0.5Pr_0.5Ga_0.85Mg_0.15O₃), which is1.56¹0^-2S cm^-1at700℃. Its ion transportnumber is above_0.9, indicating that ionic conductivity is dominant. when dopedionic radius smaller Pr in La site, it resultes in the derease of cell volume or latticedistortions, which may contribute to the transport of oxygen ions and improve theelectrical conductivity and reduce the conductivity activation energy. In the paper,when the Mg content is15%, the conductivity of La_0.4Pr_0.6Ga_0.9Mg_0.1O₃andLa_0.3Pr_0.7Ga_0.85Mg_0.15O₃at700℃is2.1910^-2S cm^-1and2.1410^-2S cm^-1,respectively. While at600℃, it reduces to_0.9210^-2S cm^-1and_0.94710^-2S cm^-1, respectively. The activation energy is_0.618eV and_0.657eV at the mid-andlow-tempertures, respectively.Co-doping induces electron or hole conductivity in electrolyteLa_0.3Pr_0.7Ga_0.85Mg_0.15O₃. When the doping concentration is below0.03, the ionicconductivity is dominant. However, the ion transport number becomes very smallwhen the doping concentration is above0.03. The conductivity ofLa_0.3Pr_0.7Ga_0.835Mg_0.15Co_0.015O₃at700℃and600℃is3.0210^-2S cm^-1and^-1.8110^-2S cm^-1, respectively. The activation energy is0.302eV in the mid-andlow-tempertures. Some electrolytes are further characterized by thermal expansion measurement.An inflexion of thermal expansion occurs around600℃. The average thermalexpansion coefficient is about10×10^-6℃^-1, which is almost equal to that of YSZ,while smaller than LSGM.With Ag as the electrodes of La_0.5Pr_0.5Ga_0.9Mg_0.1O₃-based SOFC, the maximumshort-circuit current density and maximum power density are254mA cm2and46.1mW cm2at850℃, respectively. When using Ni/BSCF as electrodes, the maximumshort-circuit current density and maximum power density are450mA cm2and105mW cm2at800℃, respectively. At high temperature, the performance of SOFCbased on Co-doping electrolytes is lower than that without Co-doping. While at thelow temperature, higher performance is achieved with Co-doping electrolyte. ForSOFC based on La_0.3Pr_0.7Ga_0.835Mg_0.15Co_0.015O₃, the maximum short-circuit currentdensity and maximum power density are161mA cm2and38.7mW cm2at600℃,respectively.In summary, doping Pr and Co in LaGaO₃-based electrolyte can effectivelyimprove the comprehensive performance at the mid-and low-tempertures, making itmore competitive in the application.