Developing new ceria-based electrolytes for low-temperature solid oxide fuel cells by sodium doping

Na doped-CeO2 (NaxCe1-xO2-δ, NDC) electrolytes with x=0, 0.05, 0.10, 0.15, 0.20 (CeO2, 0.05NDC, 0.1NDC, 0.15NDC, 0.2NDC) were synthesized and systematically characterized for low-temperature SOFCs (LT-SOFCs). DFT calculations reveal that Na doping lowers the oxygen-vacancy formation energy. Structural analysis confirms progressive lattice expansion in the four NDC samples and a maximum oxygen-vacancy concentration in 0.15NDC, while incomplete incorporation of Na yields residual Na2CO3 in 0.2NDC. Conductivity studies demonstrate negligible electronic conductivity and a peak ionic conductivity for 0.15NDC, evidencing that moderate Na doping enhances ionic transport whereas excessive dopant is detrimental. Two 0.15NDC-based SOFCs are fabricated by ceramic and dry-pressing methods, which deliver maximum power densities of 208 and 778 mW cm-2 at 550 °C, respectively, indicative of rapid ionic transport. These results establish Na doping as an effective route for developing advanced LT-SOFC electrolytes.