Optimizing Y and Pr co-doped CeO2 electrolytes for intermediate-temperature solid oxide fuel cells

Abstract

The ceria-based electrolytes with high ionic conductivity are promising for SOFCs, garnering extensive research interest. This study examines Y and Pr co-doped Ce_1-xY_x/2Pr_x/2O_2-δ (x = 0–0.30) electrolytes for IT-SOFCs. The synthesized compositions are characterized to assess their functional properties. All samples formed cubic fluorite structures at 600 °C. YPDC20 shows the highest relative density (94.8 %) and, the smallest grain size, highest dislocation density, and largest micro strain. X-ray photoelectron spectroscopy (XPS) reveals the mixed valence states of cerium (Ce⁴⁺/Ce³⁺) in both CeO₂ and YPDC20, along with coexisting Pr³⁺/Pr⁴⁺ states in YPDC20. Electrochemical impedance spectroscopy combined with capacitance calculations confirms significant differences in the contributions of grain, grain boundary, and electrode components. The study reveals that for YPDC05, the characteristic grain boundary resistance arc shifts to higher frequencies with increasing temperature, with only electrode response observed at 800 °C. As doping concentration increases, the disappearance temperature of grain boundary response significantly decreases: YPDC10 exhibits only electrode contribution at 700 °C, while higher-doped samples (x > 0.10) reached this state at 600 °C. Notably, YPDC20 demonstrates optimal performance, achieving an ionic conductivity of 1.2 × 10⁻¹ S cm⁻¹ at 800 °C—nearly two orders of magnitude higher than undoped CeO₂. This performance enhancement primarily stems from the dual effects of Y/Pr co-doping: the introduction of cations (Y³⁺/Pr^3+/4+) significantly increases oxygen vacancy concentration, while the optimized microstructure provides fast transport channels for oxygen ions. These characteristics make YPDC20 a highly promising electrolyte material for IT-SOFCs.