Preparation And Properties Of La₂NiO_4+? Oxygen-permeable Materials Based On Ruddlesden-Popper Structure

The perovskite-like materials with Ruddlesden-Popper(R-P)structure have inferior oxygen permeability than perovskite materials,but better stability,recently they have attracted much attention.We employed the dual-phase mixing and single-phase element doping methods to improve the oxygen permeability of La2NiO4+?(LNO)material with R-P structure.La2Ni1-xMoxO4+?(LNMX)powders were prepared by a sol-gel method,and La2NiO4+?-Ce0.9Gd0.1O3-?(Ce0.8Sm0.2O3-?)powders with various mass ratios were prepared by ball milling from LNO powder and Ce0.9Gd0.1O3-?(GDC)powder or Ce0.8Sm0.2O3-?(SDC)powder.The LNO-GDC,LNO-SDC and LNMX hollow fiber oxygen permeable membranes were prepared by phase inversion-sintering technology.The materials were characterized by XRD,SEM,TEM,etc.The oxygen permeability test and conductivity measurement for the prepared powders and hollow fiber membranes were also conducted.Those optimized dual-phase membranes and Mo-doped single-phase membranes with good oxygen permeability were selected to investigate the long-term CO2-resistant stability.The LNMX powders calcined at 1000 C present a typical orthogonal structure.The new phases La2MoO6 and La4Ni3O10 gradually appear when the doping content of Mo element is higher than 0.05.Among them,La2Ni0.95Mo0.05O4+?(Mo0.05)hollow fiber membrane has the best oxygen permeability with a highest oxygen permeation flux up to 3.27 mL min-1 cm-2 at 1000 C.When the purge gas changed from pure He to pure CO2 at 950 C,the oxygen permeation flux decreased from 2.88 to 2.75 mL min-1 cm-2.Although the oxygen permeation flux decreased by 4.50%,it remained stable in the subsequent 190 h.The oxygen permeation flux can be completely recovered when the purge gas was changed back to pure He.These results illustrate that the membranes possess excellent CO2 tolerance.Due to the element migration in the internal structure of the LNO-GDC,LNO-SDC dual-phase materials sintered at 1400 C,the characteristic XRD peaks of GDC/SDC shifted negatively.Also the(Gd)LNO-(La)GDC,(Sm)LNO-(La)SDC oxygen ion transport channels formed in the hollow fiber membranes.The hollow fiber membranes with 80wt.%LNO-20wt.%GDC(20GDC)and 80wt.%LNO-20wt.%SDC(20SDC)exhibit the optimum oxygen permeability in the respective systems,and the oxygen permeation fluxes of 20GDC and 20SDC at 1000? reach 3.53,3.31 mL min-1 cm-2,respectively.When the purge gas changed from pure He to pure CO2 at 950 C,the oxygen permeation fluxes of 20GDC and 20SDC decreased from 3.08,2.80 mL min-1 cm-2 to 2.80,2.57 mL min-1 cm-2,which decreased by%and 8.2%,respectively.However,it showed good stability under the CO2 atmosphere during the long-term oxygen permeability test.It was found that 20GDC has the highest oxygen permeability at 1000 C,which is 0.77 times higher than that of LNO in the same condition.While Mo0.05 has the optimum oxygen permeability at 750 C,which is 4.3 times higher than that of LNO.The conductivity of LNO-GDC/LNO-SDC decreases with the increase of the ratio of the GDC/SDC.And when the Mo doping level rises,the conductivity of LNMX decreases gradually.The TECs of LNO-GDC,LNO-SDC,and LNMX materials are close to those of the electrolyte materials in solid oxide fuel cell,which indicates that they have good thermal compatibility and presents a promising potential as cathode materials for solid oxide fuel cell.