Ionic transport mechanism of La0.9Sr0.1Ga0.8Mg0.2O2.85-(Li/Na)2CO3 composite electrolyte for low temperature SOFCs

Abstract

La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM)-(52 mol% Li2CO3: 48 mol% Na2CO3) composite was investigated as a novel electrolyte for low temperature solid oxide fuel cells (LT-SOFCs) operated at 400–600 °C. In this study, the stability of conductivity of LSGM-30 wt% (Li/Na)2CO3 composite electrolyte was been investigated by AC impedance measurements. The composite sample showed a relatively stable conductivity (0.098–0.12 S cm−1) over 120 h measurement in air at 600 °C. As the experiment time elapsed, the conductivity had a slight decline (0.085 S cm−1). Further, it was also the first time to discuss the conduction behaviours of LSGM-30 wt% (Li/Na)2CO3 composite electrolyte in various dry and wet atmospheres (nitrogen, hydrogen, oxygen, carbon dioxide and air) by electrochemical impedance spectroscopy. It was found that wet atmosphere could lower transition temperature at low temperature environment (450 °C), carbon dioxide was not inert gas for composite conduction but could improve the ionic conductivity. The value of O2− conductivity in oxygen and H+ conductivity in hydrogen was obtained by DC polarization method. Based upon the performances, the possible conduction mechanism of the composite electrolytes was discussed. The results indicated that the mixed O2−/H+/CO32− conduction happened in LSGM-(Li/Na)2CO3 composite electrolyte with the increasing dominance of CO32− conduction at high temperatures (600 °C).