Preparation And Properties Of Ta₂O₅-TiO₂ Based Solid Oxide Fuel Cell Electrolyte

With the depletion of traditional fossil fuels,the new utilization way of energy sources such as fuel cells and lithium batteries continue to emerge.Solid oxide fuel cell(SOFC)has become one of the focuses of research because of its high efficiency and environmentally friendly.Electrolytes,as the core components of SOFC,are directly related to the service life and performance of the entire battery system,and getting more and more attention.In this thesis,nano-Tantalum oxide-Titanium oxide based solid electrolyte powders were prepared by oxalate co-precipitation method.The properties of solid electrolyte powders were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD),and the optimum process parameters were determined.The relative density,electrochemical impedance spectroscopy(EIS)and coefficient of thermal expansion(CTE)of electrolytes with different dopants and different doping concentrations were calculated by Archimedes drainage method,electrochemical workstation and thermal expansion instrument.Based on the results of XRD before and after sintering of doped Fe2O3 electrolytes,the relationship between electrolyte structure of Ta2O5-TiO2-Fe2O3 system and electrical conductivity were discussed.The results show that:In electrolytes with different Fe2O3 doping ratios,when doping ratio is about 2.3%,the electrolyte has the relative density of 92.91%and the conductivity of 2.80× 10-2/cm at 800?,corresponding to the minimum activation energy of 0.9491eV.At the same time,the doped electrolyte has a low thermal expansion coefficient of 3.26×10-6K-1.In electrolytes with different Al2O3 doping ratios,when doped with 2.3%Al2O3,the electrolyte has the relative density of 86.24%and conductivity of 1.99 × 10-2S/cm at 800 ?,corresponding to the minimum activation energy of 0.9508eV.At the same time,the doped electrolyte has a low thermal expansion coefficient of 2.38×10-6 K-1.The relative density of electrolytes with different Ga2O3 doping ratio was lower than 80%.Meanwhile the conductivity of electrolyte decreased after doping with Ga2O3,and the coefficient of thermal expansion increased with the increase of doping ratio,from 3.04×10-6K-1 to 3.52×10-6K-1.The results of XRD show that the crystal type of electrolyte powder is orthorhombic crystal type,and the crystal type of sintered powder is triclinic crystal type.So the crystal type changed.The contents of FeTaO4 in impurity phase increase continuously with the increasing of Fe2v3 doping amount.When the smaller Ti4+ and Fe3+ replace the Ta5+ in polyhedron,in order to maintain electric neutrality,the O2-position around the Ta5+ in the polyhedron produces oxygen vacancy,and the adjacent O2+ in the polyhedron migrates to the position of the oxygen vacancy when excited by external energy.Thus,the process of conducting oxygen ions is completed.The occupancy of[TaO7]decahedron in the space group structure of triclinic crystal is higher than that in the space group of orthogonal crystal form,which provides a greater possibility for the generation of oxygen vacancy,and the electrolyte of triclinic crystal form has higher conductivity.