Electronic and ionic transport in Ce_0.8Pr_xTb_0.2-xO_2-δ and evaluation of performance as oxygen permeation membranes

The electronic conductivity of Ce_0.8Pr_xTb_0.2-xO_2-δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range a_O2 ≈ 10³ to a_O2 ≈ 10^-17 at 700- 900 °C by means of Hebb-Wagner polarisation. The electronic conductivity of all the Ce_0.8Pr_xTb_0.2-xO_2-δ compositions was significantly enhanced as compared to that of Ce_0.9Gd_0.1O_1.95-δ, and its value was found to increase with increasing Pr/Tb ratio. The ionic mobility of Ce_0.8Pr_xTb_0.2-xO_2-δ is similar to that of Ce_{1- 2δ}Gd_2δO_2-δ at the same oxygen vacancy concentration. The calculated oxygen flux of a Ce_0.8Pr_xTb_0.2-xO_2-δ membrane is significantly enhanced relative to that of a Ce_0.9Gd_0.1O_1.95-δ membrane at high oxygen activities of the permeate gas (a_O2 ^an > 10^-15) due to the enhanced electronic conductivity of the Ce_0.8Pr_xTb_0.2-xO_2-δ compounds. Interference between the ionic and electronic flows has a significant positive effect on the deliverable oxygen flux, as evaluated for Ce_0.8Pr_0.2O_2-δ (1).