Phase stability and electrochemical properties of Fe-doped LSGM solid electrolyte for IT-SOFCs

Abstract

$La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.2}O_{3-\delta}$ (LSGM8282) perovskites show superior ionic conductivity and chemical stability, and are regarded as promising candidates for the electrolyte of intermediate temperature solid oxide fuel cells (IT-SOFCs). Efficiency of fuel cell using LSGM is related to the electrical conductivity of the electrolyte, since the minor charge carriers in the electrolyte, i.e., free electrons and electron holes, could result to a short circuit current. The studies of the conductivity of LSGM with a low concentration of transition metal ($\lt 8.5 mol%$) are still limited. Ishihara et al. investigated the electronic conductivity in cobalt doped LSGM with the ion blocking method. Electronic conductivities at various temperatures in $La_{0.8}Sr_{0.2}Ga_{0.8}Mg_{0.15}Co_{0.05}O_{3-\delta}$ (LSGMC5) and electronic conductivities at in LSGM8282 doped with various amount of cobalt were reported. It was considered that minor free electron and hole conductivity caused by the redox reactions. The properties of the single cell have a strong effect on the polarization resistance of the electrode supported on the electrolyte beside the dominant effect on the ohmic resistance of the cell. The single cells with transition metal doped lanthanum gallate electrolyte exhibited a low ohmic resistance and electrode polarization resistance. It was assumed that the properties of the charge carriers in the electrolyte could play a major role in determining the cell performance In chapter III, we discuss the phase stability and conductivity of Fe-doped LSGM with a “Sr-rich” composition (25 mol%), or $La_{0.75}Sr_{0.25}Ga_{0.8}Mg_{0.2 -x}Fe_xO_{3-\delta}$ (x = 0-0.08) and report the results of optimized composition for a promising electrolyte composition. It is of significance to systematically investigate the crystal structure, because the investigation brings the useful information to examine the oxide ion conduction mechanism. Thus we crystallographic analys...