Developing sodium-doped ceria-based electrolytes for low-temperature solid oxide fuel cells

• Na doping in CeO2 lowers the oxygen-vacancy formation energy, facilitating faster ionic transport. • A Na doping concentration of 0.15 molar ratio (0.15NDC) yields the highest oxygen-vacancy concentration and peak ionic conductivity. • 0.15NDC-based SOFCs achieve maximum power densities of 208 and 778 mW·cm−2 at 550°C depending on the fabrication method (ceramic vs. dry-pressing). • Moderate Na doping is a promising strategy for developing high-performance low-temperature SOFC electrolytes, whereas excessive dopant is detrimental.