Effect of A/B-Site Non-stoichiometry on the Structure and Properties of La0.9Sr0.1Ga0.9Mg0.1O3-delta Solid Electrolyte in Intermediate-Temperature Solid Oxide Fuel Cells

摘要

(La0.9Sr0.1)(x)(Ga0.9Mg0.1)(y)O3-delta [(LS)(x)(GM)(y)] (x = 0.97, 1.00, 1.03; y =1.00 and x = 1.00; y = 0.97, 1.00, 1.03) electrolyte is prepared through a sol-gel method followed by sintering at 1300 degrees C for 10h. The microstructures of the samples are characterized by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The electrical and thermal stability properties are measured by means of electrochemical impedance spectroscopy (EIS) and thermal expansion coefficient (TEC), respectively. It is shown that phase purity could improve by adjusting the non-stoichiometry of A/B-site. This, in turn, affects the conductivity and thermal expansion of the solid electrolyte. The samples with B-site defects [LS(GM)(0.97)] are found to exhibit the best phase purity and density with minimal grain boundary/total resistances, and superior thermal stability. The conductivity of LS(GM)(0.97) is 1.56 time higher than that of LSGM. The average thermal expansion coefficient of LS(GM)(0.97) at 50-850 degrees C is 4.13% lower than that of LSGM. The maximum power density of single cells containing LS(GM)(0.97) electrolyte could reach 0.54 W cm(-1) at 800 degrees C, which is 16.7% higher than that of cells containing LSGM electrolyte. The stability test for over 120 h at 800 degrees C indicates a slight decrease in performances during the first 10 h, but no significant differences in electrode polarization are observed even after long-term operation. These findings suggest the potential applications of LS(GM)(0.97) as a novel electrolyte for intermediate-temperature solid oxide fuel cells.