The Performance Study Of Sr₂Fe_1.4Ni_0.1Mo_0.5-xNb_xO_6-? Materials As Cathodes For SOFC And Catalysts For DeNO_x

Perovskite oxides have been widely used as electrode materials for intermediate temperature solid oxide fuel cell?IT-SOFC?and automobile tail gas treatment due to its excellent oxidation and reduction stability,thermal stability and catalytic activity.Sr₂Fe_1.5Mo_0.5O_6-??SFM?,as one of the new perovskite oxides,has good electrochemical performance as the SOFC cathode.The doping modification on SFM materials is a hotspot in the field of IT-SOFC.At the same time,the perovskite materials are being used in the field of catalytic denitrification.Therefore,in this paper,power generation of SOFC is combined with denitrification technology to study the efficiency and electrochemical activity of SFM materials for removing NO_x in the air.Firstly,Sr₂Fe_1.4Ni_0.1Mo_0.5-xNb_xO_6-?(SFNi_0.1MNb_x,x=0,0.05,0.1 and 0.15)materials co-doping with Ni and Nb were synthesized by the one-step combustion method,and its microstructure,physical and chemical properties and electrochemical properties were studied.X-ray diffraction?XRD?is used to study the phase structures of the materials,and the results show that all the samples maintain orthorhombic structure.The unit cell volume and the thermal expansion coefficient of the sample increase slightly with the increase of Nb content.Scanning electron microscopy?SEM?is used to characterize the microstructure of the samples and the results show that the obtained samples had uniform porous network structures,which is favorable for the gas diffusion and transmission,thus improving the electrochemical performance of the electrodes.The XPS results show that the ratio of Fe²⁺/Fe³⁺and Mo⁶⁺/Mo⁵⁺in SFNi_0.1MNb_x is changed with the Nb doping,leading to the change of conductivity.SFNi_0.1MNb_0.05 show the best electrochemical performance,with the lowest polarization resistance of 0.21 and 0.11?·cm² and the highest power density of803 and 1260 mW·cm^-2 at 750 and 800 ^oC,respectively.Therefore SFNi_0.1MNb_0.05 has good performance as IT-SOFC cathode material.The characteristics of SFNi_0.1MNb_x materials as catalysts in selective catalytic reduction?SCR?are also studied respectively,including denitration efficiency,specific surface area,redox performance,acid strength and surface acidity of the catalysts.The results show that the denitrification activity of SFNi_0.1MNb_x perovskite materials increases with the increase of temperature.The redox performance is improved due to the addition of Nb element.When x=0.05,the material has the largest specific surface area and the maximum strong acid concentration.Therefore,the anode supported single SOFC with SFNi_0.1MNb_0.05 cathode is assembled for testing discharge performance and denitration efficiency.The results show that an competitive adsorption exists between NO and O₂which results in increased cell impedance and lower output power when exhaust gas as oxidation gas compared with that under air condition.The lower oxygen partial pressure of cathode in exhaust gas makes the open circuit voltage of cell less than 1.0 V.The conversion rate of NO increased with the increase of operating temperature,indicating that SOFC can output electric energy by converting NO into N₂.That is to say,SOFC possesses the ability of removing NO from the air and producing electricity at the same time.On the base,combing SOFC with denitrification technology can be betterly investigated further in the future.