Effect Of Lanthanum Doping On Perovskite High-temperature In-situ Exsolution And Its Application In Solid Oxide Cells(SoCs)

High-temperature in-situ segregation,as a highly efficient method for preparing ceramic-supported metal,has received extensive attention from catalyst manufacture.When the ceramic of perovskite structure is in a reductive atmosphere,the ion of B-site will be segregation on the surface of material.If the B-site ion can be reduced to a metal element by the atmosphere,the material surface will be precipitated by the metal particles,i.e.in-situ exsolution of the metal particles in perovskite materials.The exsolution of the metal particles will be evenly distributed on the ceramic substrate surface which are ideal catalyst shapes.For example,Sr₂Fe_1.4Ni_0.1Mo_0.5O₆,a solid oxide cell（SOC）anode material,will exsolute nanometer-level Fe-Ni particles at the surface in the reductive atmosphere,and it can enhance the catalytic performance of the material.However,the relative larger radii of Ni ionic and less charge it has lead to excessive precipitation of metal particles,and at last destroy the surface of ceramic.Therefore,La³⁺,a high valence and small size ion,was used to restrain the excessive resolution of metal particles at the surface and to keep highly catalytic activities.First,a sol-gel method was used to synthesize the La_xSr_2-3x/2Fe_1.4Ni_0.1Mo_0.5O₆ceramic powder.It was found that with the increase of La³⁺doping,the lattice parameters were changed,which was consistent with the different ion radii.Using SEM to observe the surface morphology of particle precipitation in reducing atmosphere.We can find that with the addition of La elements,the number of particles precipitates decreased,and the holes on the surface of the ceramic substrate also disappeared,which showed that La element did inhibit the particle precipitation and maintained the catalyst’s surface topography.When the amount of La doped arrive 0.3,the dissolved metal particles are evenly distributed while the ceramic substrate is basically smooth,which can be considered as the best doping value.And in EDS test,it was confirmed that the precipitated particles were metal Fe-Ni alloys,which were consistent with the in-situ dissolution theory.For material performance,in TPR test,with the increase of La element,the corresponding temperature of Fe³⁺and Ni²⁺reduction peaks is reduced,as well as the peak area,which is consistent with the decrease of precipitated metal particle’s size and amount.As to the conductivity test,dropped 0.3 La ceramic sample has the highest conductivity in the 10%H₂/N₂ environment,which due to La_0.3SFNM’s best surface topography.For the cell performance,La_xSr_2-3x/2Fe_1.4Ni_0.1Mo_0.5O₆（L_XSFNM）|LSGM|L_XSFNM Symmetrical Anode cell was prepared by Tap Casting-Impregnation method.When x=0.3,the polarization impedance is the lowest,which is 0.15 Ohm·cm^-22 and0.29 Ohm·cm^-2 at 750℃and 650℃,respectively.Similarly,the L_XSFNM|LSGM|SmBa_0.5Sr_0.5Co₂O₆（SBSCO）single cell prepared in the same way,and we can find best performance cell at x=0.3.The maximum power density at 750℃and 650℃are 1.26W/cm2 and 0.90 W/cm2,respectively.Compare the cell without drop La element which maximum power density are 1.04W/cm² and 0.59W/cm²,the addition of La elements will indeed enhance the performance of the electrode performance.Finally,we used La_0.3Sr_1.55Fe_1.4Ni_0.1Mo_0.5O₆(La_0.3SFNM)material as the fuel electrode catalyst,and prepared La_0.3SFNM|LSGM|SBSCO electrolysis cell.with50%H₂O/H₂ as electrolytic gas,and exert 1.5V voltage,the current density reaches2.67A/cm² and 1.92A/cm² under the condition of temperature 800℃and 700℃,that is,hydrogen production rate is 18.63ml·min^-1cm^-2and13.40ml·min^-1cm^-2.In pure CO2electrolysis at the same temperature,the production rate of CO at 1.6V Voltage is14.7ml·min^-1cm^-22 and 7.0ml·min^-1cm^-2 respectively.and the electrolytic performance is fine.From the above experimental results,the addition of La has inhibited the dissolution of Fe-Ni particles,and as fuel electrode materials in the fuel cell and electrolytic cell improve performance.