Preparation and Electrochemical Performance of Rare-Earth Doped CeO₂-Based Electrolytes: A Systematic Comparison of Sm³⁺, Gd³⁺, Y³⁺ and La³⁺

The reduction of operating temperature for solid oxide fuel cells (SOFCs) imposes higher requirements on the ionic conductivity of electrolyte materials. CeO₂-based electrolytes have attracted considerable attention due to their superior ionic conductivity in the intermediate-to-low temperature range. However, pure CeO₂ tends to develop electronic conduction under reducing atmospheres, which severely limits its practical application. In this study, CeO₂-based electrolyte materials doped with four rare-earth ions, namely Sm³⁺, Gd³⁺, Y³⁺ and La³⁺, were synthesized via a co-precipitation method. The effects of dopant species on the crystal structure, microstructure, sintering behavior, electrochemical performance and single-cell output performance were systematically investigated. The results indicate that all doped samples form single-phase solid solutions with a cubic fluorite structure. Gd³⁺/La³⁺ doping significantly promotes the densification of CeO₂. Among all samples, Sm- and Gd-doped CeO₂exhibit the highest oxygen vacancy concentration. Sm-doped CeO₂ achieves an ionic conductivity of 0.04 S/cm at 700 ℃, and the single cell based on this electrolyte exhibits a maximum power density of approximately 90 mW/cm², which is substantially superior to those of the other doping systems. This comprehensive study demonstrates that Sm-doped CeO₂ is the most promising electrolyte material among the four systems for intermediate-to-low temperature SOFCs applications.