Sintering-Driven Optimization of Multi-Ionic SDC-Na2CO3 Nanocomposite Electrolytes for Low-Temperature Solid Oxide Cell Applications

Composite electrolytes based on samarium-doped ceria (SDC) and sodium carbonate were synthesized via a single-step coprecipitation method and evaluated for low-temperature solid oxide cell (SOC) applications. The impact of sintering temperature on phase composition, microstructure, conductivity, and stability was systematically studied. X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and solid state nuclear magnetic resonance analyses revealed strong interfacial interactions between SDC and Na2CO3. Electrochemical impedance spectroscopy in air and 4 % H2 atmospheres demonstrated multi-ionic conduction with dominant protonic transport under dry reducing conditions. Conductivity values above 20 mS/cm at 600 ◦C were achieved in samples sintered at 700 ◦C, although these exhibited significant decay under 72 h exposure to a humidified atmosphere. Samples sintered at 850 and 900 ◦C showed improved densification (up to 97 %), allowing proton conduction to follow the same hydration-based transport mechanism observed in conventional perovskite proton conductors, independent of the surrounding gas composition. Open-circuit voltage experiments conducted at 600 ◦C on highly dense pellets revealed values close to the theoretical Nernst potential, confirming gas tightness and low electronic leakage compared to the pure SDC phase. These findings demonstrate that the SDC-Na2CO3 nanocomposite offers promising transport properties for SOC applications, with trade-offs between conductivity and stability driven by sintering-induced microstructural changes.