Preparation And Electrochemical Properties Of SMM And SFM Double Perovskite SOFC Anode Materials

Solid oxide fuel cells（SOFCs）is an all-solid-state device that can directly convert the chemical energy stored in fuel into electric energy.Due to its high fuel applicability,high efficiency and environmental friendliness,SOFCs has attracted wide attention worldwide in recent years.Traditional SOFCs nickel-based anodes have the advantages of good electrical conductivity,high catalytic activity and low cost.But the direct use of hydrocarbon fuels can cause serious problems,such as carbon deposition and sulfur poisoning.Therefore,it is necessary to find suitable alternative anode materials.Double perovskite anodes（A2BB’O6）,with Mixed ion-electron Conductivity（MIEC）,redox stability,excellent sulfur resistance and carbon deposition resistance,are used as alternative anodes for SOFCs running directly on carbon-based fuels.However,the double perovskite anode has some problems such as low conductivity and low catalytic activity.This paper discusses and researches the above problems.（1）Firstly,the Sr2（MgMo）1-x/2MnxO6-δ（SMMMx）（x=0～0.6）anode powder prepared by Sol-gel method,and designed the electrolyte supported type single cell SMMMx-GDC‖GDC‖YSZ‖GDC‖LSCF+GDC.The effects of Mn ion doping on the crystal structure and electrochemical properties of SMM materials were compared.XRD results show that double perovskite phase can be synthesized at 1300℃at x=0.1,0.2.Mo5+/Mo6+and Mn3+/Mn4+contents were calculated by XPS peak separation.When x=0.2,the concentration of lattice oxygen vacancy and tolerance factor t were both increased,indicating that the conductivity and crystal symmetry of oxygen ions were improved.SMMM0.2 cell has the best electrochemical performance,with a maximum power density of 224 mW/cm2 and polarization resistance of 0.739Ω·cm2 at 850℃.In conclusion,the incorporation of B-site Mn ions doping is helpful to improve the electrochemical performance of SMM materials.（2）In order to further reduce the operating temperature of SOFCs,GDC was selected to replace YSZ as electrolyte material,and Sr2Fe1.5-xMnxMo0.5O6-δ（x=0～0.4）（SFMXM）anode powder with better conductivity and catalytic activity was synthesized by Sol-gel method.Designed SFMxM-GDC‖GDC‖LSCF-GDC single cell,explore in Fe-site Mn ions on the effects of doping.XRD results showed that SFMXM synthesized pure double perovskite phase at 1200℃ at x=0.1,0.2.The Fe2+/Fe3+and Mo5+/Mo6+contents were calculated by XPS peak separation.When x=0.2,the oxygen vacancy concentration and tolerance factor t were increased,and the oxygen ion conductivity and crystal symmetry were improved.TG-DTA results show that SFM and SFM0.2M have the same weight loss region and thermal effect,and both have a large amount of oxygen loss to provide sufficient oxygen vacancy capacity.The SEM section of the cell shows that SFMXM and GDC phases with sub-micron particle size are evenly mixed,and the composite anode presents a three-dimensional porous structure,which can effectively reduce the diffusion resistance of gas in the electrode.The electrochemical performance of SFM0.2M cell is the best,the maximum power density is 192 mW/cm2 at 800℃,and the anode polarization impedance is only 0.049Ω·cm2.Therefore,the incorporation of B-site Mn ions doping is helpful to improve the electrochemical performance of SFM materials.（3）To further improve the electrochemical performance of SFM materials,select A-site doping elements,through the synthesis of Sol-gel method Sr2-xGdxFe1.5Mo0.5O6δ（x=0～0.4）（SGXFM）anode powder,design the SGXFM-GDC‖GDC‖LSCF-GDC single cell,The effects of A-site Gd3+doping on the crystal structure and electrochemical properties of SFM materials were investigated.XRD results showed that SGxFM synthesized double perovskite phase at 1200℃.With the increase of Gd3+doping amount,the diffraction peak shifted and the crystal structure was destroyed.SG0.1FM has higher Fe2+/Fe3+,Mo5+/Mo6+ratio and maximum oxygen vacancy concentration by XPS peak splitting calculation.With the increase of Gd3+doping amount,the tolerance factor t value of SGXFM decreases gradually,and the symmetry of crystal structure weakens gradually.TG-DTA results also showed that SG0.1FM had the highest oxygen loss.It can be observed from the SEM section of the cell that the composite anode presents a three-dimensional porous structure,in which SGxFM and GDC phases are evenly mixed,which can provide enough TPB reaction sites for hydrogen dissociation and adsorption.The results show that SG0.1FM anode material has the best performance.The maximum power density at 800℃ is 264 mW/cm2,and the anode polarization impedance is only 0.021 Ω·cm2.It indicates that Gd3+doping at the A-site can affect the valence of the B-site element to obtain considerable oxygen loss,thus improving the electrochemical performance.