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

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.