Effect of La3+, Pr3+, and Sm3+ triple-doping on structural, electrical, and thermal properties of ceria solid electrolytes for intermediate temperature solid oxide fuel cells

Abstract

In the present study, we have investigated the effect of La3+, Pr3+, and Sm3+ triple-doping on structural, electrical, and thermal properties of ceria (Ce1–x(Lax/3Prx/3Smx/3)O2-δ). X-ray diffraction studies confirm the formation of samples with single-phase cubic-fluorite structure (JCPDS PDF File No: 34-0394). The lattice parameter values increases with increasing the dopant concentration (from 5.4190 Å to 5.4503 Å), shows that the dopants get totally dissolved into Cerium site. All the prepared samples were sintered at 1300 °C for 4 h. The values of relative densities were found to be higher than 95% and the high value is observed for the composition LPS8 i.e. 97.8%. The calculated crystalline size values were found to be in the range of 46 and 53 nm. Scanning electron microscope and energy dispersive spectroscopic techniques reveal the surface-microstructure and presence of elemental confirmation in the compositions. The average grain size values were found to be in between 231 and 366 nm. Raman spectroscopy study reveals the existence of oxygen vacancies in all the compositions and estimated concentration of oxygen vacancies is found to be high for LPS8 composition. The impedance spectroscopy revealed the total ionic conductivity and activation energies of all the compositions. The composition Ce0.76La0.08Pr0.08Sm0.08O2-δ (LPS8) displays the highest total ionic conductivity i.e. 0.043 S/cm with low activation energy i.e. 0.76 eV. Matched thermal expansion coefficient of the sample Ce0.76La0.08Pr0.08Sm0.08O2-δ with already existing electrode materials, makes it as an effective electrolyte material for the intermediate temperature–solid oxide fuel cell applications.