Synthesis and sintering of Gd-doped CeO2 electrolytes with and without 1 at.% CuO dopping for solid oxide fuel cell applications

Nano-sized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce0.8Gd0.2O2−δ and Ce0.79Gd0.2Cu0.01O2−δ possessed similar powder characteristics, including cubic fluorite crystalline structure, porous foamy morphology and agglomerated secondary particles composed of gas cavities and primary nano crystals. Nevertheless, after ball-milling these two powders exhibited quite different sintering abilities. A significant reduction of about 400 °C in densification temperature of Ce0.79Gd0.2Cu0.01O2−δ was obtained when compared with Ce0.8Gd0.2O2−δ. The Ce0.79Gd0.2Cu0.01O2−δ pellets sintered at 1000 °C and the Ce0.8Gd0.2O2−δ sintered at 1400 °C exhibited relative densities of 96.33% and 95.7%, respectively. The sintering of Ce0.79Gd0.2Cu0.01O2−δ was dominated by the liquid phase process, followed by the evaporation-condensation process, Moreover, Ce0.79Gd0.2Cu0.01O2−δ shows much higher conductivity of 0.026 S cm−1 than Ce0.8Gd0.2O2−δ (0.0065 S cm−1) at a testing temperature of 600 °C.