Role of the salt phase in GDC and alumina-based composites

Abstract

In ceria-salt composite systems, the reasons for a two-order enhancement in conductivity relative to that for doped ceria are still unclear. In our attempt to gain further insight in the phenomenon of conduction, we have investigated two different sets of composites: alumina-salt and ceria-salt. Various compositions in the two-phase composite system involving gadolinium-doped ceria (GDC) and alkali carbonates were prepared and characterized. Later, GDC was replaced with alumina, and similar compositions were prepared and characterized to examine the contribution of the GDC phase to the overall conductivity. The conductivity curves, in spite of variations in composition, exhibited a transition at about 500°C, which also corresponds to the melting temperature of the salt phase. From an analysis of the conductivity data, it is observed that at high temperatures, the salt phase plays a significant role in the conduction enhancement. However, at lower temperatures, GDC primarily appears to contribute significantly to the conductivity.

Compositional and microstructural effects in composite electrolytes for fuel cells

“…The absence of the transition temperature suggests a distinct role of the carbonate phase in the conductivity of this composite, in agreement with the strong chemical interaction between phases evidenced by XRD (Figure 2(b)). However, recently published results on similar composites based on AO show the preservation of the sharp conductivity jump close to the carbonates melting temperature 27. This conflicting evidence suggests that the exact microstructure and phase composition of these composites, depending on the starting AO powder particle size and adopted mechano‐thermal processing route, might influence significantly the electrical properties of these materials.…”

Fundamentals and Catalytic Applications of CeO2-Based Materials

“…There has been a convergence to study two-phase electrolyte materials on account of the highly improved ionic conductivity arising from the binary conductive nature (O 2– /H + ), and at present, the interest is predominantly focused on this type of electrolyte in which the doped-ceria is combined with other salts. Without doubt, the most explored and promising composite is obtained by combining ceria with carbonates, − although recently some skepticism has arisen for these systems that present several question marks. Ceria-carbonate composites are generally accessed by means of mechanical mixing or by infiltration techniques.…”