Improving the performance of oxygen transport membranes in simulated oxy-fuel power plant conditions by catalytic surface enhancement

The stability of dual-phase oxygen transport membranes consisting of 70 vol% (Y2O3)0.01(Sc2O3)0.10(ZrO2)0.89 and 30 vol% MnCo2O4 (10Sc1YSZ-MCO (70-30 vol%)) was investigated in simulated oxy-fuel power plant fluegas (250 ppm SO2, 5% O2, 3% H2O, balance CO2). Additionally, the influence of catalytic porous backbones on the performance of the membrane was studied in the same conditions.

The chemical stability of the dual-phase membrane was investigated by X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FE SEM). The tests performed before and after the exposure to the simulated flue gas showed excellent chemical stability. Electrochemical impedance spectroscopy (EIS) measurements were performed on activated (Ce-Pr catalyst) and non-activated porous catalytic backbones made of: (i) (Y2O3)0.08(ZrO2)0.92 (8YSZ), (ii) 8YSZ-MCO (40–60 vol%),(iii) 10Sc1YSZ-MCO (40–60 vol%), (iv) 10Sc1YSZ-MCO (70-30 vol%), and (v) Ce0.8Tb0.2O2-δ (CTO) - NiFe2O4 (NFO) (40–60 vol%) to achieve a better understanding of the oxygen surface reactions (especially in SO2 and CO2 containing atmospheres).

The lowest polarization resistances (Rp) were found for 10Sc1YSZ-MCO (40–60 vol%) and CTO-NFO (40–60 vol%) porous backbones. Oxygen permeation tests realized on 10Sc1YSZ-MCO membranes demonstrated that the catalytic porous backbones can significantly influence the oxygen permeation flux, and improvements of up to55% were achieved.

Both EIS and oxygen permeation measurements showed a significant influence of SO2 on the oxygen oxidation/reduction reactions (increaseof Rp, decrease ofoxygen permeation fluxes) due to SO2 adsorption and blocking of active sites for the oxygen reactions. Nevertheless, no microstructural degradation was found after SO2 exposure andinitial Rp values and oxygen permeation fluxes could be recovered in most cases.