Synthesis, structural and electrochemical properties of oxyapatites La10Si6−xNixO27−δ as electrolyte material for solid oxide fuel cells

There has been a global increase in energy demand, which has necessitated a considerable interest on renewable energy, amongst which are fuel cells. Research efforts in the Solid Oxide Fuel Cells (SOFC) is towards developing electrolyte materials that operate at intermediate temperatures: 500–800 °C which significantly reduce device cost. The purpose of this work is to prepare lanthanum silicate apatite using a low temperature solution synthesis method as electrolyte material in SOFC and enhance the ionic conductivity via Ni doping at the Si site. Nickel doped apatite La10Si6−xNixO27−δ (x = 0; 0.2; 0.4; 0.8) were synthesized from succinate precursors by co-precipitation and calcined at 1000 °C. The oxyapatites were characterized by Fourier Transformed Infrared analysis, X-ray diffraction, microstructural and elemental analyses, and conductivity measurements on the sintered pellets was carried out by the complex impedance spectroscopy. The X-ray diffraction results confirm the presence of apatite phase with hexagonal structure. The conductivity measurements of the samples show that the ionic conductivity increases with increasing Ni2+ content and temperature. The highest conductivity value, 2.07 × 10–2 S cm−1 at 750 °C was observed for La10Si5.2Ni0.8O27−δ electrolyte material which is higher than most values reported in the literature. Therefore, the synthesized nickel doped lanthanum silicate oxyapatites show enhanced conductivity and are suitable candidates as electrolyte for intermediate temperature SOFC.