Non-doped CeO₂-carbonate nanocomposite electrolyte for low temperature solid oxide fuel cells

CeO₂ is an oxygen nonstoichiometric material for the coexistence of redox pair of Ce³⁺ and Ce⁴⁺, even under an oxidizing atmosphere, and its self-doping is fulfilled bases on the multivalence characteristics. It has been served in versatile applications, including fuel cells and catalysis. Excellent electrochemical performances of solid oxide fuel cell (SOFC) have been achieved at intermediate and low-temperature range based on doped cerium oxide electrolyte. In this study, we utilize its self-doping form to prepare core-shell structure bi-phase nano-composite of CeO₂ and alkali carbonate (Li₂CO₃, Na₂CO₃ and K₂CO₃) through a two-step synthesis method. SEM, TEM, XRD, and EIS measurements were applied to characterize the morphology, crystal size, the ionic conductivity of the electrolyte, and the electrochemical performance of resulting ceramic fuel cells. An exceptional ionic conductivity of 0.34 S cm⁻¹ was generated at 550 °C in air, significantly different from its insulating property of the perfect CeO₂ phase. A power density of 910 mW cm⁻² was also achieved as the highest electrochemical performance of a single cell. The multi-ionic conduction behavior of CeO₂-carbonate is also discussed. The results reveal an effective approach to develop alternative SOFC electrolyte materials for low-temperature, high-performance energy conversion applications.