Synthesis of transition metal doped lanthanum silicate oxyapatites by a facile co-precipitation method and their evaluation as solid oxide fuel cell electrolytes

Transition metal doped apatite La(10)Si(6−x)Co(x)O(27−δ) (x = 0.0; 0.2; 0.8) and La(10)Si(5.2)Co(0.4)Ni(0.4)O(27−δ) are synthesized by co-precipitation method followed by sintering. The precursor precipitates and apatite products are characterized by XRD, FTIR, TGA/DTA, Raman Spectroscopy, SEM-EDX and electrochemical impedance spectroscopy. The presence of apatite phase with hexagonal structure is confirmed through the XRD results. The conductivity measurements of the samples sintered at 1000 °C show that the ionic conductivity increases with increasing content of Co(2+) doping into apatite that is further increased by co-doping of Ni(2+). The Co doped apatite (La(10)Si(5.2)Co(0.8)O(27−δ)) exhibited conductivity of 1.46 × 10(−3) S cm(−1) while Co–Ni co-doped sample (La(10)Si(5.2)Co(0.4)Ni(0.4)O(27−δ)) exhibited highest conductivity of 1.48 × 10(−3) S cm(−1). The maximum power density achieved is also for Co, Ni co-doped sample i.e., 0.65 W cm(−2) at 600 °C. The results represented show that Co and Ni enhances the SOFC performance of apatite and makes it potential electrolyte candidate for solid oxide fuel cell application.