Stability and performance of robust dual-phase (ZrO₂)_0.89(Y₂O₃)_0.01(Sc₂O₃)_0.10-Al_0.02Zn_0.98O_1.01 oxygen transport membranes

Dual-phase composite oxygen transport membranes consisting of 50 vol% Al_0.02Zn_0.98O_1.01 and 50 vol% (ZrO₂)_0.89(Y₂O₃)_0.01(Sc₂O₃)_0.10 were successfully developed and tested. The applicability of the membrane in oxy-fuel power plants schemes involving direct exposure to flue gas was evaluated by exposing the membrane to gas streams containing CO₂, SO₂, H₂O and investigating possible reactions between the membrane material and these gases. The analyses of the exposed composites by x-ray diffraction (XRD), x-ray fluorescence (XRF), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Raman spectroscopy revealed excellent stability. Additionally, an electrical conductivity measurement over 900 h confirmed that the composite is stable under prolonged exposure to CO₂. However, an instability of the dual-phase membrane under oxygen partial pressures below P_O2~10⁻⁴ atm. was found. Oxygen permeation tests on a 1 mm thick self-standing membrane resulted in an oxygen flux of 0.33 mL_N min⁻¹ cm⁻² at 925 °C in air/N₂. Stability tests in CO₂ with 3 vol% O₂ demonstrated the potential for the use of 10Sc1YSZ-AZO dual-phase membranes in oxy-combustion processes involving direct exposure to flue gas.