In recent years there are extensive activities on ceria-based two-phase materials, so-called composite electrolytes, used for advanced 300-600ºC fuel cell technology. In the ceria-based two-phase materials, typical ceria are samarium or gadolinium doped ceria (SDC or GDC) as one major function phase. This report makes a short review on this new type of the fuel cell material science and technology, including our latest developments on two-phase nanocomposites design, theoretical studies, advanced characterizations, microstructures on the two-phase region of interfaces, with emphasize on electrical conductivity studies on new functional materials possessing superionic conduction at low temperatures. We have first successfully developed some ceria-based two-phase materials can reach the conductivity 0.1 S/cm as low as at 300ºC being equal to YSZ at 1000ºC conductivity.

Mesoporous materials show obvious kinetic advantages over bulk materials used as components in SOFC (solid oxide fuel cell), e.g. forming continuous ionic/electronic conduction pathways. Using the ceria-based two-phase electrolytes combined with mesoporous components, the fuel cell technology has been demonstrated with power out put at 550ºC reaching 1W/cm². It has tremendously reduced working temperature of conventional SOFC from 1000ºC to 500ºC. The new approach and advanced fuel cell performance demonstrated have been benefited by the interfaces and interactions in the interfacial regions between the electrolyte and mesoporous electrode, that may significantly enhance the current and power outputs. Besides, the electrolyte material architecture of the two-phase composite displays a new scientific principle in material design and development where conductivity enhancement or superionic conduction is caused by the interfacial mechanism.