Dual-phase membrane based on LaCo0.2Ni0.4Fe0.4O3-x-Ce0.8Gd0.2O2-x composition for oxygen permeation under CO2/SO2-rich gas environments

A dual-phase material with high ambipolar conductivity composed by the perovskite LaCo0.2Ni0.4Fe0.4O3-delta (LCNF) as the electronic phase and the fluorite Ce0.8Gd0.2O2-delta (CGO20) as oxide-ion conductor is proposed for use as oxygen transport membrane. The chemical compatibility between both materials depends on the synthesis method, i.e. one-pot sol-gel synthesis leads to the formation of the fluorite and the perovskite phases, as well as a third NiO-based phase. The formation of this last phase can be avoided by previously stabilizing the phases separately. The composite material shows high electrical conductivity, i.e., 7.25 S cm(-1) at 800 degrees C for LCNF-CGO20 with NiO impurity, and 2.6 S cm(-1) at 800 degrees C for LCNF-CGO20. A maximum oxygen flux, J(O-2), of 0.74 ml min(-1) cm(-2) is obtained at 1000 degrees C for a surface-activated membrane in Air/Ar gradient at ambient pressure. The membranes were tested under i) 30% CO2 in Ar, and ii) 250 ppm of SO2 in 30% CO2 in Ar, reproducing oxyfuel-like conditions. Oxygen flux decreases in these atmospheres, especially at temperatures below 900 degrees C, due to competitive adsorption of these gases with the O-2. After CO2 and SO2 exposure, initial oxygen fluxes are recovered when switching back to Ar sweeping at temperatures above 900 degrees C. Nevertheless, at temperatures < 900 degrees C the original J(O-2) before SO2 exposure is not fully recovered and postmortem FESEM images reveal the membrane surface degradation in SO2.