Effects of B-site Nb doping on the CO₂ resistance and rate-controlling step of Ce_0.8Gd_0.2O_2−#delta#–Pr_0.6Sr_0.4Co_0.5Fe_0.5O_3−#delta# dual-phase membranes

Dense fluorite–perovskite-type dual-phase membranes of 60% Ce_0.8Gd_0.2O_2−#delta#–40% Pr_0.6Sr_0.4Co_0.5Fe_0.4Nb_0.1O_3−#delta# (CG–PSCF_0.4N_0.1) were prepared successfully via ethylenediaminetetraacetic acid (EDTA)–citric acid method. Subsequently, the effects of B-site Nb doping on the CO₂ resistance, oxygen permeability, and rate-controlling step of Ce_0.8Gd_0.2O_2−#delta#–Pr_0.6Sr_0.4Co_0.5Fe_0.5O_3−#delta# (CG–PSCF) were systematically investigated. The results of high-temperature in situ X-ray diffraction under pure CO₂ atmosphere, X-ray photoelectron spectra, and oxygen permeation tests indicated that the thermal stability and CO₂ resistance of CG–PSCF could be improved significantly via Nb doping. Furthermore, by measuring the distributions of permeation resistances at certain temperatures using the adopted permeation model, the rate-controlling step was determined, and the oxygen permeability degradation mechanism of CG–PSCF was attributed to the increased bulk diffusion resistance caused by phase transition of PSCF and formation of carbonate. All the results demonstrated that Nb doping has a positive effect on the oxygen permeation stability of CG–PSCF, and CG–PSCF_0.4N_0.1 dual-phase membranes have promising potential for oxy-fuel combustion.