| La doped SrTiO3(LST)is a promising oxide ceramic anode material because of its high electronic conductivity,matching coefficient of thermal expansion with ZrO2 based electrolytes,good sulfur resistance and excellent physical and chemical stability in redox atmosphere.Chen et al.found that there was obvious interfacial chemical reaction between stoichiometric LST and electrolyte 1CeO2-10Sc2O3-89ZrO2(ScSZ)at high temperature to produce La2Zr2O7(LZO)with poor catalytic activity and low conductivity,which significantly reduced the electrochemical performance of the cell.The introduction of A-site deficiencies can effectively inhibit the high temperature chemical reaction between stoichiometric LST and electrolyte ScSZ.Doping Al,Sc and Ga at B site of(La0.25Sr0.75)0.9TiO3((LS)0.9T)can effectively inhibit the element diffusion between(LS)0.9T and ScSZ,and Al doping is the most effective.However,Al doping reduces the catalytic activity of(LS)0.9T for anodic electrochemical reaction.In this paper,the catalytic activity of the anode was improved by doping Fe,Co,Ni,Mg and Mn elements with catalytic activity at the B site of(LS)0.9T.The phase structure and high-temperature chemical stability of LST materials with single doping and double doping were studied,and the influence mechanism of B-site doping on the high-temperature chemical stability of LST anode was studied by first principles calculation.The main contents are as follows:(1)(La0.25Sr0.75)0.9Ti0.9M0.1O3(LSTM0.1,M=Fe,Co,Ni,Mg,Mn)powders were synthesized by Sol-gel method.XRD results show that the LSTM0.1 forms a good cubic perovskite phase.The composite pellets of LSTM0.1/ScSZ annealed at 1200℃for 30 h were characterized by XRD,it was found that the chemical compatibility of LSTM0.1(M=Fe,Co,Ni)and ScSZ electrolyte was better than that of LSTM0.1(M=Mg,Mn)at high temperature.The first principles calculations show that the doping of Fe,Co,Ni,Mg and Mn in La0.25Sr0.75Ti0.875M0.125O3 at B site increases the vacancy formation energy(VFE)of Ti in La0.25Sr0.75TiO3.The chemical compatibility between LSTMn0.1 and ScSZ is poor because of the doping of Mn at B-site makes the VFE of Ti in La0.25Sr0.75TiO3 increase less.Although the VFE of Ti is greatly improved by doping Mg at B site,the TiO6 octahedron adjacent to Mg is seriously distorted after doping,which also makes the chemical compatibility between LSTMg0.1 and ScSZ poor.(2)B-site double doped LSTAl0.08Mx(M=Fe,Co,Ni,Mn;x=0.02,0.06)anode materials were synthesized by sol-gel method.XRD results show that the crystal structure of LSTAl0.08Ni0.06 is distorted due to the high concentration of Ni doping,and the other seven kinds of double doped powder samples form good cubic perovskite phase.The XRD results shows that the eight double doped LSTAl0.08Mx anode materials and ScSZ electrolyte had good chemical compatibility after annealing at 1200℃ in air for 30 h.Doping Fe,Co,Ni,Mn and other elements at B site results in different degrees of alloy oxides precipitated at B site of LSTAlM,which indicates that there is a critical B site doping concentration for oxide precipitation in B site double doping.(3)In the high concentration doped LSTMx,the VFE of the doped element itself can also affect the stability of the compounds.The RVFE of dopants in La0.25Sr0.75Ti0.875M0.125O3(M=Fe,Co,Ni,Mg)with high concentration B-site doping is calculated by first principles method,it is found that the VFE of Fe,Co,Ni is much lower than that of Ti in La0.2sSr0.75TiO3.The experimental results of high concentration B-site doping show that the high temperature chemical compatibility between(La0.25Sr0.75)0.9Ti1-xMxO3(M=Fe,Ni)and electrolyte ScSZ becomes worse when the doping concentration x increases from 0.1 to 0.2,which supports the first principle calculation in this paper. |
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