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

Abstract

Transition metal doped apatite La₁₀Si_6−xCo_xO_27−δ (x = 0.0; 0.2; 0.8) and La₁₀Si_5.2Co_0.4Ni_0.4O_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 Co²⁺ doping into apatite that is further increased by co-doping of Ni²⁺. The Co doped apatite (La₁₀Si_5.2Co_0.8O_27−δ) exhibited conductivity of 1.46 × 10⁻³ S cm⁻¹ while Co–Ni co-doped sample (La₁₀Si_5.2Co_0.4Ni_0.4O_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.