Synthesis and characterization of lanthanum silicate apatite by gel-casting route as electrolytes for solid oxide fuel cells

Lanthanum silicate oxyapatite, La10Si6O27 is successfully synthesized by a water-based gel-casting technique. The effect of calcination and sintering temperatures on the conductivity is investigated in detail in the temperature range between 300 and 800 °C by the impedance spectroscopy. The highest oxygen ion conductivity is 1.50 × 10−3 S cm−1 at 500 °C and 3.46 × 10−2 S cm−1 at 800 °C for an apatite electrolyte sintered at 1650 °C, which is one order of magnitude higher than that synthesized by the conventional solid state reaction route under the same sintering conditions. The thermal expansion coefficient (TEC) of the as-synthesized apatite is 9.7 × 10−6 K−1. A solid oxide fuel cell using La10Si6O27 as an electrolyte shows an open circuit potential of 1.06 V and power output of 7.89 mW cm−2 at 800 °C. The results demonstrate the potential of the silicate oxyapatite materials synthesized by the gel-casting as an alternative electrolyte in solid oxide fuel cells.