Preparation And Properties Of Non-Metallic Ion Doped SrCoO_3–? Oxygen Permeable Membrane

Perovskite-type(ABO_3–?)mixed conductor oxygen permeable membrane with theoretically 100% oxygen selectivity is a kind of ceramic material with electronic and oxygen ions conductivity.The migration of electrons and oxygen ions are based on the overlap of the d metal orbits of the transition metal ions and the p orbits of the oxygen ions and oxygen vacancies,respectively.However,in the development of oxygen permeable membranes for more than 30 years,the trade-off effect between oxygen permeability and stability has always limited its practical industrial applications.At present,doping metal cations at the A or B site in the perovskite structure is the main strategy for developing high performance perovskite-type oxygen permeable membranes.Recently,numerous scholars have reported that anion-doped perovskite-type oxygen permeable membranes can construct a fast transmission channel for oxygen ions,which has attracted attention.In addition,it has been reported in the relevant literature that the doping of non-metallic cations can not only stabilize the cubic phase structure of the perovskite solid oxide fuel cell cathode,but also improve the electronic conductivity,but the application of this strategy in the field of mixed conductor oxygen permeable membranes is still blank.Therefore,in order to solve the problem that high oxygen permeability and high stability cannot be acquired simultaneously,this thesis proposes to optimize oxygen permeability and stability of perovskite mixed conductor oxygen permeable membrane by doping non-metallic cations and/or anions.Two strategies of non-metallic cation doped as well as non-metallic cation-anion co-doped strontium cobalt oxide(SrCoO_3–?)were the research subject of study.The effect of non-metallic ion doping strategy on the structural stability and oxygen permeability of perovskite materials was systematically studied.The main conclusions obtained are as follows:1.A series of Sr Co_1-x Px O_3–??100_x = 0,3,5,7,10?powders with different levels of P⁵⁺ ions were prepared by the sol-gel method and prepared into dense sheet shaped oxygen permeable membrane.X-ray diffraction analysis proved that the cubic phase of SrCoO_3–? oxygen permeable membrane can be stabilized to room temperature through doping P⁵⁺ ions.However,when the doping level was greater than 5%,inpurity phase of Sr₅?OH??PO₄?₃?PDF # 44-0654?was generated.Though the performance of P⁵⁺-doped membrane is slightly lower than that of SrCoO_3–?,the stability of SrCoO_3–? membrane below 850 ? is improved.When the doping amount of non-metallic P⁵⁺ ion reachs 5%,the oxygen permeability and stability were the best,and reached 1.70 m L·min^-1·cm^-2 at 825 ?.Beside,oxygen permeation flux maintained at 0.3 m L·min^-1·cm^-2 without any attenuation was observed in more than 150 hours long-term stability testing at 600 ?.2.In order to improve the permeability of the non-metallic P⁵⁺ ion doping,Sr Co_0.95P_0.05O_3–?Cl_0.05 oxygen permeable membrane with the co-doping of non-metallic cation-anion(P⁵⁺/Cl^-)was developed.The results show that the non-metallic cation-anion co-doping can not only stabilize the cubic phase structure of the SrCoO_3–? perovskite oxygen permeable membrane,but also improve the oxygen permeation flux,3.15 m L·min^-1·cm^-2 at 950 ?,and 1.95 m L·min^-1·cm^-2 at 825 ?.Both of which were higher than non-metallic P⁵⁺ ion doped Sr Co_0.95P_0.05O_3–? oxygen permeable membrane and close to SrCoO_3–? oxygen permeable membrane.