Enhanced ionic conductivity and reduced electrical conductivity in Ce0.8Gd0.2O1.9: Effect of calcium Co-doping

Gd 3+ -doped ceria Ce 0.8 Gd 0.2 O 1.9-δ (GDC) is a well-known electrolyte for solid oxide fuel cell technology. This study is designed to understand the influence of Ca 2+ doping in GDC on the electrical conduction behavior, in particular the electronic conductivity, of the resulting electrolytes. Using a sol-gel method, Ce 0.8 Gd 0.2-x Ca x O 1.9-δ (C x GDC; x = 0.01, 0.03, 0.05, and 0.10) electrolyte materials were synthesized and studied. It revealed that Ca 2+ doping significantly improved the total conductivity of the electrolyte and, at the same time, suppressed its electronic conductivity. At 750 °C, C 0.03 GDC has a total conductivity of 0.069 S cm −1 , 1.4 times higher than that of GDC, whilst has an electronic conductivity of 4.13 × 10 −5  S cm −1 , 81% lower than that of GDC. The electrolyte-supported C 0.03 GDC single cell delivers a maximum power density of 0.399 W cm −2 at 750 °C, more than 40% higher than the GDC single cell. Additionally, the open circuit voltage of the C 0.03 GDC single cell reaches 0.98 V at 550 °C, in contrast to the 0.90 V of the GDC cell. The superior performance of this C 0.03 GDC single cell is attributed to not only the enhanced total conductivity but also the suppressed electronic conductivity of the C 0.03 GDC electrolyte.