Magnesium doped lanthanum silicate with apatite-type structure as an electrolyte for intermediate temperature solid oxide fuel cells

Abstract

Electrical properties of magnesium doped lanthanum silicates as an electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs) have been investigated. Dense ceramic disks of La9.6Si5.7Mg0.3O26.1 with apatite-type structure have been prepared by sintering first at 1600 °C and then at 1750 °C. The ionic conductivity is remarkably increased by magnesium doping and La9.6Si5.7Mg0.3O26.1 has exhibited a conductivity of 30 mS cm−1 at 800 °C. Owing to low activation energy, the compound shows higher conductivity than yttria stabilized zirconia below 780 °C. Oxygen gas concentration cell measurements revealed that the compound is an oxide ion conductor. A solid oxide fuel cell using La9.6Si5.7Mg0.3O26.1 as an electrolyte was found to work at 608, 706 and 805 °C with power densities of 1.3, 5.8 and 20.0 mW cm−2, respectively, which demonstrates that magnesium doped lanthanum silicates can be used for IT-SOFC electrolytes. The low power densities are probably due to insufficient performance of Pt paste electrodes.