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 Ce0.8PrxTb0.2-xO2-δ (x = 0, 0.05, 0.10, 0.15, 0.20) was determined in the oxygen activity range aO2 ≈ 103 to aO2 ≈ 10-17 at 700- 900 °C by means of Hebb-Wagner polarisation. The electronic conductivity of all the Ce0.8PrxTb0.2-xO2-δ compositions was significantly enhanced as compared to that of Ce0.9Gd0.1O1.95-δ, and its value was found to increase with increasing Pr/Tb ratio.

The ionic mobility of Ce0.8PrxTb0.2-xO2-δ is similar to that of Ce1- 2δGd2δO2-δ at the same oxygen vacancy concentration. The calculated oxygen flux of a Ce0.8PrxTb0.2-xO2-δ membrane is significantly enhanced relative to that of a Ce0.9Gd0.1O1.95-δ membrane at high oxygen activities of the permeate gas (aO2 an > 10-15) due to the enhanced electronic conductivity of the Ce0.8PrxTb0.2-xO2-δ compounds.

Interference between the ionic and electronic flows has a significant positive effect on the deliverable oxygen flux, as evaluated for Ce0.8Pr0.2O2-δ (1).