Protonic conduction properties of nanostructured Gd-doped CeO₂ at low temperatures

The electrical properties of nanostructured Gd-doped CeO₂ (n-GDC) as a function of temperature and water partial-pressure were investigated using ac and dc measurements. For n-GDC, protonic conductivity prevails under wet condition and at low temperatures (< 200°C), while oxygen ionic conductivity occurs at high temperatures (> 200°C) under both dry and wet conditions. The grain boundaries in n-GDC were highly selective, being conductive for protonic transport but resistive for oxygen ionic transport. The protonic conductivity reaches about 4 × 10^-7 S/cm at room temperature (RT).