Preparation And Properties Of KNbO₃-based Proton Conductor Materials

Solid electrolyte,as a carrier of solid state ionic conduction,has attracted more and more attention of researchers.As an important functional material in solid electrolyte,proton conductors have been widely used in fuel cells,electrochemical sensors,electrochemical synthesis of ammonia and hydrodehydrogenation.BaCeO3,SrCeO3,CaZrO3,BaZrO3 and KTaO3-based solid electrolyte materials have been found to have some application value.The sintering temperatures of the first four matrix materials are all very high,about 1600℃.However,Ta in KTaO3-based proton conductors is expensive,so it is necessary to find a kind of proton conductor material with good sintering performance and low sintering temperature.Nb and Ta are in the same main group,and their physical and chemical properties are very similar.The ionic radius of Ta5+ and Nb5+with coordination number of six are both 0.064nm,but the price of Nb is relatively low.Therefore,we turn our attention to KNbO3-based solid electrolyte materials that have not been systematically studied as proton conductors.In this study,the B site of KNbO3 was modified by doping.The doping ions were divided into two series,the first series was doped by Ti4+,Zr4+ and Hf4+ in B site.The second series is doped by In3+,Sc3+,Yb3+ in B site.The results of this experiment are as follows:1.Seven kinds of solid electrolyte ceramics,KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf)and KNb0.9M0.1O3-α(M=In,Sc,Yb),were prepared by high temperature solid state reaction at 1000℃.XRD results showed that KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf,In,Sc,Yb)were synthesized.2.The relative densities of KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf,In,Sc,Yb)were determined by Archimedes and they were all>94%,and the relative densities of KNb0.9Yb0.1O3-α were 99%.SEM images showed that the microstructure of the seven materials were compact and had no obvious porosity.3.The absorption edge wavelengths and bandgap widths of KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf,In,Sc,Yb)were analyzed and calculated by UV-Vis diffuse reflectance spectroscopy.The order of bandgap widths was:KNbO3>KNb0.9In0.1O3-α>KNb0.9Yb0.1O3-α>KNb0.9Sc0.1O3-α>KNb0.9Hf0.1O3-αKNb0.9Zr0.1O3-α>KNb0.9Ti0.1O3-α,Among them,KNb0.9In0.1O3-α has the largest band gap of 3.274 eV,which indicates that the electronic conductivity is the weakest.4.The impedance spectra of KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf,In,Sc,Yb)solid electrolyte materials were measured by AC impedance method under experimental conditions,and the conductivities of each material at different temperatures were analyzed and calculated.Among them,the conductivity of KNb0.9In0.1O3-α is the highest,reaching 4.71×10-3S·cm-1 at 800℃.5.The Arrhenius curves,Arrhenius equations and activation energies of KNbO3,KNb0.9M0.1O3-α(M=Ti,Zr,Hf,In,Sc,Yb)were.obtained by fitting and calculating the conductivity data.Among the six doped proton conductors,KNb0.9Ti0.1O3-α has the lowest activation energy of 0.75eV,which is theoretically most favorable for ion conduction.6.The proton transfer number of KNb0.9M0.1O3-α(M=Ti,Zr,Hf)was studied by concentration cell method.The results show that the proton transfer number of KNb0.9Hf0.1O3-α is the highest among the three materials,and the proton transfer number is>0.99 within 500℃,which indicates that the material is a pure proton conductor at 500℃.Among the three proton conductors KNb0.9M0.1O3-α(M=In,Sc,Yb),the number of proton transfer of KNb0.9In0.1O3-α varies the least with temperature.The number of proton transfer of KNb0.9In0.1O3-α is more than 0.92 when the working temperature is less than 600℃.7.The electron transfer number of KNb0.9M0.1O-α(M=Ti,Zr,Hf,In,Sc,Yb)was measured and calculated by concentration cell method.The results show that the band gap width measured by ultraviolet spectrum is consistent with the electron transfer number.It further shows that KNb0.9M0.1O3-α has the weakest electron transfer ability.