Influence Of A-site Nonstoichiometry On Microstructure And Electrical Properties Of LSCF-GDC Composite Cathode

The polarization loss of Solid Oxide Fuel Cell,SOFC occurs mainly at the cathode reaction process, so the property of SOFC depends largely on its cathode material performance. As a kind of medium temperature solid oxide fuel cell, Cobalt base perovskite material is one of the most promising cathode materials, which owns high oxygen ion diffusion coefficient and good ion-electron conductivity.However, the catalytic activity of cobalt base electrolytes reduced obviously under the condition of medium temperature and impurities are easy to generate between cobalt base electrolytes and yttria-stabilized zirconia under the condition of high temperature. Domestic and foreign related research have proved that the nonstoichiometry is an effective method to improve material performance. By the perovskite material Lao.6Sro.4Coo.2Feo.8O3-δ(LSCF) as the research subject, this paper explored the effect of A-site nonstoichiometry on the material performance and determined the best proportion measurement. The best compound proportion was also explored through the research method of adding Gd2O3 doping CeO2(Ceo.8Gdo.2O2, GDC) into Lao.6Sro.4Coo.2Feo.8O3-δ (LSCF). The performance of the composite cathode which owns optimal proportion of LSCF and GDC was also explored. The main research content of this paper is as follows:(Lao.6Sro.4)xCoo.2Feo.803-5(x=0.95-1.05) and Ceo.8Gdo.202-δ(GDC) were prepared using the sol-gel method. The structure of (Lao.6Sro.4)xCoo.2Feo.803-δ(x=0.95-1.05) and Ceo.8Gd0.202-s(GDC) were measured by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Conductive performance was also tested by electrochemical impedance spectroscopy (EIS). The experiment result indicates:1. All of the (Lao.6Sro.4)xCoo.2Feo.803-δ(x=0.95～1.05) presented rhombic structure. Test results of FE-SEM show that the ample still retained good porosity cathode and electrolyte connection after the proper change of A-site nonstoichiometry. (Lao.6Sr0.4)1.05Co0.2Feo.803-δ has the minimum interfacial polarization resistance, which results the best electrochemical performance.2. LSCF and GDC composite cathode is mainly composed of perovskite structure and cubic fluorite phase composition. GDC can significantly inhibit the growth of the LSCF grain, increasing the porosity of materials. The sample owns the minimum interfacial polarization resistance when the GDC mass fraction is 40%.3. The crystal structure of (LS)1.05CF-40GDC composite cathode cannot change, Still composed of perovskite structure and cubic fluorite phase. (LS)1.05CF-40GDC cathode interface polarization resistance compared to a single than stoichiometric cathode orcomposite cathode are significantly reduced.