Fast Oxygen Separation Through SO2- and CO2-Stable Dual-Phase Membrane Based on NiFe2O4–Ce0.8Tb0.2O2-δ

Composite membranes with enhanced oxygen permeability and unprecedented stability in oxyfuel-like gas environments are reported. Specifically, 60 vol% NiFe2O4 - 40 vol% Ce0.8Tb0.2O2-δ (NFO-CTO) composite has been successfully obtained by one-pot fabrication method showing both spinel and fluorite pure phases. Narrow grain size distribution centered around 1 μm and homogeneous distribution of grains is attained, as well as percolative pathways from side to side of the dual-phase membranes. The composite resisted a stability test in wet SO2 and CO2 containing gas at 800 °C for 170 h, which represents a step forward toward its use in oxyfuel power plants. The conductivity of both phases is investigated as a function of temperature and oxygen partial pressure (pO2). Oxygen separation in this kind of NFO-doped-ceria composite membranes occurs via the separate ambipolar transport through the two distinct percolating networks. Oxygen permeation flux values of 0.17 mL·min–1·cm–2 and 0.20 mL·min–1·cm–2 are achieved at 1000 °C when argon and pure CO2 are used as sweep gas, respectively, through a 0.68 mm-thick membrane. Experiments at 900 °C showed that the material is stable and effective in pure CO2 atmospheres and the oxygen permeation is even improved after 76 h on CO2 stream.