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 Na 2 CO 3 . Electrochemical impedance spectroscopy in air and 4 % H 2 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-Na 2 CO 3 nanocomposite offers promising transport properties for SOC applications, with trade-offs between conductivity and stability driven by sintering-induced microstructural changes. • SDC-Na 2 CO 3 composite electrolytes sintered between 700 and 900 °C were studied. • Protonic conductivity decreased with increasing sintering temperature in dry H 2 . • Degradation was registered under humidification for low sintering temperature. • Composites sintered at T ≥ 850 °C display significant conduction properties. • Composites sintered at 900 °C demonstrated near-theoretical OCV values at 600 °C.