Impact of rare-earth co-dopants in ionic conductivity of ceria-based materials for SOFCs

This study involved the synthesis of rare-earth (Sm 3+ and Nd 3+ ) co-doped ceria (CeO 2 ) through the co-precipitation method, utilizing sodium hydroxide (NaOH) as the precipitating agent to improve the ionic conductivity of the materials intended for use as an electrolyte of solid oxide fuel cells (SOFCs) applications. The crystal structure and morphology of the synthesized materials were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The absence of secondary phases indicates the material's phase purity. Structural analysis revealed that the lattice constant ( a ) and average crystallite size ( L ) increased with higher Nd 3+ concentrations as a result of substituting a minor amount of Nd 3+ with Sm 3+ , which possesses larger ionic radii in comparison to Sm 3+ . SEM images showed that particle size grew from 52 n m to 102 n m as the Nd 3+ concentration increased predicting the grain growth suppressing grain boundaries. Energy-dispersive X-ray spectroscopy (EDX) confirmed the elemental composition that agreed with the starting composition of the synthesized materials. Impedance analysis indicated a decrease in grain and grain boundary resistances with increasing Nd 3+ content up to 10 %. Consequently, ionic conductivity was enhanced, reaching a maximum value of 6.24 × 10 − 2 S / c m at 750 ° C as compared to single-doped ceria (SDC) for the composition. Ce 0.80 Sm 0.10 Nd 0.10 O 2 − δ , with the lowest activation energy recorded at 0.53 ± 0.01 e V . These findings indicate that NaOH-assisted co-precipitation is a beneficial technique for synthesizing co-doped ceria materials. The resulting materials possess ionic conductivity comparable to that synthesized with ammonium carbonate and urea as precipitating agents, making them interesting candidates for SOFC electrolyte applications requiring high ionic conductivity.