Chemical diffusivity and ionic conductivity of GdBaCo2O5+δ

The transport properties of layered perovskite GdBaCo2O5+δ (GBCO), which has recently been proposed as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs), are investigated as a function of oxygen partial pressure (OPP) over the oxygen partial pressure range of 10−4 ≤ pO2 (atm) ≤ 0.21 at 1073 ≤ T (K) ≤ 1323. The increase in total conductivity with increasing temperature below the low-temperature, order–disorder transition indicates a semiconductor-type behaviour with an activation energy of 0.42 eV. When OPP is increased to air pressure at a fixed temperature, the total conductivity increases with an apparent slope (∂log σ/∂log pO2) of 1/10 to 1/22. The maximum oxygen ion conductivity, as extracted from the oxygen permeation measurements, is around 0.01 S cm−1 under the nitrogen condition, which strongly supports the potential for cathode application. The chemical diffusion coefficient (D˜) and surface exchange coefficient (κ) are also calculated from the d.c. conductivity relaxation measurement and the values are best fitted by the following two equations:D˜   (cm2 s−1)=1.88×10−2 exp−0.77 eVkT, κ   (cm s−1)=1.37×100 exp−0.86 eVkT