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.