Microstructure and electrical conductivity of La10Si6O27–La0.9Sr0.1Ga0.8Mg0.2O2.85 composite electrolytes for SOFCs

Abstract

Composite ceramic electrolytes with heterostructure have attracted wide attention from the scientific community due to their enhanced conductivity and stability compared with single component electrolytes. Along these lines, in this work, to improve the conductivity of lanthanum silicate, a series of La10Si6O27 (LSO) - La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) electrolytes were developed, which were composed of apatite/perovskite heterostructure. The phase composition, heterogeneous structure, and morphology of the samples were investigated by performing X-ray diffraction (XRD), transmission electron microscopy (TEM) measurements, as well as, field emission scanning electron microscopy (FE-SEM) for in-depth analysis. In addition, the Archimedes method was employed to test the relative density of the samples. X-ray photoelectron spectroscopy (XPS) was used to examine changes in oxygen vacancies at different LSGM contents. Compared with the pure LSO material, the content of oxygen vacancies increases significantly and the conductivity is highest when the LSGM content is 10 %, which indicates that the newly formed oxygen vacancies in the composite LSO-LSGM electrolyte play an important role in improving the ionic conductivity. At 400 °C, the conductivity of 90 wt%LSO:10 wt%LSGM was 3.4 times that of pure LSO, and at 600 °C, the conductivity of 90 wt%LSO:10 wt%LSGM was an order of magnitude higher than that of pure LSO. From the electrochemical impedance spectra (EIS) analysis, it was shown that the small resistance achieved by the grain boundary was the main reason for its excellent performance. Our results provide valuable insights for the design of more composite electrolytes for intermediate-temperature SOFCs.