Oxide ionic conductivities of apatite-type lanthanum silicates and germanates and their possibilities as an electrolyte of lower temperature operating SOFC

Electrical properties of LaxM6O12+1.5x (M = Si, Ge) as an electrolyte for solid oxide fuel cell (SOFC) have been investigated. In LaxSi6O12+1.5x and LaxGe6O12+1.5x of x = 8-11, the highest conductivities were achieved at x = 9.7 (La9.7Si6O26.55) and x = 9.0 (La-9.0(GeO4)(6)O-1.5), respectively. The conductivity of La-9.0(GeO4)(6)O-1.5 was higher than that of La9.7Si6O26.55 in a temperature region higher than 700 degrees C, and the conductivity (2.4 x 10(-3) S cm(-1)) of La9.7Si6O26.55 at 400 degrees C was higher than that (8.3 x 10(-5) S cm(-1)) of La-9.0(GeO4)(6)O-1.5. The power densities of SOFC (H-2 vertical bar Pt vertical bar electrolyte (thickness: 1 mm) vertical bar Pt vertical bar O-2) using La-9.0(GeO4)(6)O-1.5 as an electrolyte were 14.3 mW cm(-2) (700 degrees C) and 24.0 mW cm(-2) (800 degrees C). The corresponding SOFC using La9.7Si6O26.55 was found to work even at lower temperatures of 400 and 500 degrees C with power densities of 0.011 and 0.12 mW cm(-2). The SOFC (H-2 vertical bar Ni-Sm0.2Ce0.8O1.9 vertical bar electrolyte vertical bar Ba0.55Sr0.5Co0.8Fe0.2O2.5 vertical bar air) using 0.3 mm thickness La9.7Si6O26.55 electrolyte gave the 3.4 mW cm(-2) power density at 500 degrees C. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.