Development Of High Oxygen Permeability Mixed Ion Electron Conductor Oxygen Permeable Membrane

Oxygen permeable membranes（OPM）are dense membranes with both electronic and ionic conductivity and are of great interest in carbon capture technology,membrane reactors,industrial oxygen production,solid oxide fuel cells and other applications.Due to the theoretical 100%selective oxygen permeability of mixed ion electron conductor（MIEC）OPM,efforts have been made in recent years to develop（MIEC）OPM materials such as Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δand La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ.The oxygen permeability and stability of these chalcogenide based OPMs are difficult to achieve in practice(oxygen permeability of at least 1.0 m L min^-1 cm^-2and stable operation for more than 3000 h under various conditions),therefore there is an urgent need to develop more active and stable OPMs.In this paper,a series of chalcogenide MIEC OPM materials,Sr_1-xCo_0.98Ti_0.01Ta_0.01O_3-δ（x=0,0.02,0.05,0.1）,and Sr_1-xCo_0.98Ti_0.01Ta_0.01O_3-δ(S_0.98CTT)with good oxygen permeability and stability were developed.With good ionic conductivity and fluorite oxide Ce_0.9Gd_0.1O_2-δ（GDC）were blended to produce a 60GDC-40S_0.98CTT biphasic OPM with excellent stability.A series of characterisations of the prepared powders and membranes were carried out to investigate the physicochemical properties of the materials and detailed performance tests were carried out on the prepared membranes.The main elements of the research in this paper are as follows:（1）A series of Sr_1-xCo_0.98Ti_0.01Ta_0.01O_3-δ（x=0,0.02,0.05,0.1）materials with A-site metal cation defects were prepared by the solid phase method based on the Sr Co_0.98Ti_0.01Ta_0.01O_3-δ（SCTT）chalcogenide oxide configuration using the defect principle,followed by the hydrostatic method to produce.A series of single-phase oxygen permeable diaphragms with good densities were prepared.Compared to the non-defective SCTT,Sr_0.98Co_0.98Ti_0.01Ta_0.01O_3-δ(S_0.98CTT)with a defect value of x=0.02 exhibited superior oxygen permeability,with an oxygen permeability of 1.12 m L min^-1 cm^-2 at 850 ^oC for 0.8 mm.Under inert atmosphere,S_0.98CTT also showed good stability,with no significant decrease in oxygen permeability after200 h of stability testing.（2）S_0.98CTT,a single-phase material with excellent oxygen permeability,was mixed with GDC in different weight ratios(GDC:S_0.98CTT=50:50;60:40;70:30)in a two-step process to prepare a series of biphasic powders.A series of biphasic OPMs were then pressed using the hydrostatic method.The effects of different weight ratios of the two phases on the membrane properties were systematically investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）and oxygen permeability testing.The results show that the addition of GDC is beneficial to the ion phase transport,increasing the oxygen ion surface exchange rate and improving the stability of the structure,but when too much GDC is added,it will hinder the resistance of the oxygen ion bulk phase transport and reduce the oxygen permeability.Since GDC does not react with CO₂,the stability of the biphasic oxygen permeable membrane was found to be stable with increasing GDC content when tested under CO₂ atmosphere.By evaluating the oxygen permeability and stability of the membrane,it was determined that 60:40 was the optimum weight ratio of the two phases in the GDC-S_0.98 CTT mixed phase material.The oxygen permeability of the 1 mm thick 60GDC-40S_0.98CTT biphasic membrane reached 0.51 m L min^-1 cm^-2 at 850 ^oC.Moreover,the membrane was stable for 200 h under CO₂ atmosphere without any significant degradation of oxygen permeability.