Design of Micro-Structure at Atom Level in Dy Doped CeO2 Solid Electrolytes for Fuel Cell Applications

Rare earth doped ceria compounds are fluorite related oxides which show oxide ionic conductivity higher than yttria stabilized zirconia in oxidizing atmosphere. As a consequence of this, considerable interest has been shown in application of these materials for ‘low (below 500°C)’ temperature operation of solid oxide fuel cells (SOFCs). In this study, the nano-sized powders of DyxCe1-xO2-x/2 (x=0.15 and 0.2) were prepared using ammonium carbonate co-precipitation method. To design the nano-structure in aforementioned materials, the round shape particles were prepared in nano-scale. The combined process of Spark Plasma Sintering (SPS) and Conventional Sintering (CS) was examined for fabrication of nano-structured doped CeO2 solid electrolytes. The nano-structural features in the (SPS+CS) specimen and CS specimen were observed using transmission electron microscopy (TEM). This micro-analysis suggested that the micro-domain with distorted pyrochlore structure exists in the grain of these materials. The conducting properties in the specimens were strongly influenced by the micro-domain size. It is found that the present combined process minimized the micro-domain size and maximized the conductivity in the specimens. Also nano-structured Dy doped CeO2 sintered bodies in the present study had wide ionic domain and high transport number of oxygen. This suggests that fabricated sintered bodies are suitable for the solid electrolyte in low temperature operated SOFCs. It is concluded that a control of micro-domain size is a key for development of high quality doped CeO2 electrolytes for fuel cell application. It is expected that advanced solid electrolytes for clean energy production will be produced by a design of nano-structure in rare earth doped CeO2 solid electrolyte.