Preparation and Characterization of Mixed Protonic-Electronic Conducting Membrane

Author:Zhuang Li Bin

Supervisor:wang hai hui


Degree Year:2019





Mixed protonic and electronic conducting(MPEC)membrane is a kind of materials with protonic conductivity and electronic conductivity,which exhibit infinite selectivity to hydrogen theoretically.In order to meet the demand of industrialization,MPEC membrane must possess high hydrogen permeation flux and good stability.Currently,doping metallic ions and constructing dual-phase membrane are the methods to improve the performance of hydrogen permeable membranes,but the hydrogen permeability of membranes are still too low.Therefore,in order to improve the hydrogen permeability and stability of membranes,the paper chose the nonmetallic ions to dope into the membranes.And we studied the effect on the crystal structure,conductivity,permeability and stability of the membranes by doping nonmetallic ions.Lastly,the metal-ceramic dual-phase membrane was constructed to further improve the hydrogen permeability as well as the stability of perovskite type oxides.Firstly,series of different ratios of nonmetallic phosphorus ion doped lanthanum oxides La5.5W1-xPxO11.25-δ(x=0,0.1,0.2,0.3)were synthesized by the solid state method.The phase structure and hydrogen permeability of membranes were studied respectively.From the results of XRD,the oxides maintained the cubic phase structure after being sintered at 1550 oC for 10h.During the hydrogen test,the phosphorus ion doped membranes possessed higher hydrogen permeation flux.Secondly,Mo-doped lanthanum tungstate oxide was doped with the nonmetallic phosphorus ion and La5.5W0.6Mo0.4-xPxO11.25-δ(LWMPx,x=0,0.05,0.1,0.2)membranes were prepared.The effect on the conductivity,hydrogen permeability and stability of the materials had been studied.The protonic conductivity and hydrogen permeation flux of LWMP0.025membrane was improved.At 1000 oC,the permeation flux through LWMP0.025 membrane was 0.127 mL min-1 cm-2.Additionally,during the long term hydrogen permeation test at 950oC,the attenuation trend of hydrogen permeation through LWMP0.025 membrane was slower than that of LWM,indicating that the doping phosphorus ion inhibited the volatilization of Mo ion.Thirdly,nonmetallic fluoride ion was doped into the perovskite type oxides.Series of BaCe0.5Fe0.5O3-δFx(x=0,0.025,0.05,0.1)oxides were prepared and sintered to the dense membranes.It was found that the composition of BaCeO3 and BaFeO3 among the fluoride ion doped oxides were quite different.Moreover,the flouride ion effected the valance state of Fe elements and the binding energy of lattice oxygen.Besides,the hydrogen permeability of the corresponding membranes were studied and it was found that all the fluoride ion doped hydrogen permeable membranes possessed better hydrogen separation performance.Lastly,in order to further improve the electronic conductivity of the perovskie oxides,the metal Ni was introduced into the BaCe0.85Fe0.15O3-δceramic oxides,constructing the metal-ceramic dual phase membrane.Among the dual phase membrane,the metal Ni served as the individual electron transport channel while the ceramic oxides acted as the proton transport channel.The microstructure and element distributions of the dual phase membrane were studied.At the same time,the effect of testing temperature,dry or wet conditions,hydrogen partial pressure on the hydrogen permeation flux through the dual phase membrane were also been investigated.Moreover,the stability of the hydrogen permeability of membrane was studied.At 1000 oC,the hydrogen permeation flux through the dual phase membrane was as high as0.325 mL min-1 cm-2,which was four times higher than that the single phase membrane.During the long term test at 850 oC,the hydrogen permeation flux kept constant with the number of0.19 mL min-1 cm-2 for 50 hours.