| With the transformation of global energy,new energy materials have gradually become the focus of research,in which the demand for energy conservation is becoming more and more intense,and the solid oxide fuel cell,which is known as green and pollution-free and high power generation efficiency,has become a new energy use mode with great potential.During the research and development of solid electrolytes,it is a trend to reach the middle and low temperature（873-973K）gradually.And electrolyte having better electrical properties at lower working temperature is the focus of research.Therefore,it is necessary to develop an electrolyte material which can be used in medium and low temperature environment,which can promote the research of medium and low temperature fuel cells.In this paper,a new co-doped material Ta1-x-yTixRyO2.5-δ（R=Co、Sn、Nb、Cr,x=0.077,y=0-0.053）was synthesized by the oxalate co-precipitation method,and used as a novel electrolyte for medium-temperature solid oxide fuel cells（IT-SOFC）.The phase composition,microstructure,electrical properties and thermodynamic properties of the co-doped tantalum oxide-based electrolyte materials were investigated and characterized.The influence factors of the electrical properties of tantalum-based electrolytes were analyzed.Also the relationship between oxygen vacancies and electrical properties in the electrolyte structure was studied.The performance of the co-doped electrolyte of each doping element is studied as follows:at a working temperature of 973K,the co-doped electrolyte Ta0.89Ti0.077Cr0.033O2.5-δhas a conductivity of 1.48×10-1 S/cm,linear expansion coefficient is 3.09×10-6 K-1;co-doped electrolyte Ta0.89Ti0.077Sn0.033O2.5-δconductivity is 0.76×10-1S/cm,linear expansion coefficient is 3.03×10-6 K-1;co-doped electrolyte Ta0.89Ti0.077Nb0.033O2.5-δconductivity up to 1.18×10-1 S/cm,linear expansion coefficient is2.89×10-6 K-1;co-doped The electrolyte Ta0.91Ti0.077Co0.013O2.5-δhas a maximum conductivity of 0.43×10-1 S/cm and a linear expansion coefficient of 3.06×10-6 K-1.It is found that the conductivity of tantalum oxide based electrolyte is related to the cation radius of doped element,which can be described by effective factors.The co-doped tantalum-based electrolytes of the four doping elements all have low thermal expansion coefficients and belong to low-expansion materials.This property makes the electrolyte have good thermal cycling properties.All co-doped tantalum-based electrolytes have good thermal stability.The pure phase tantalum oxide has two crystal forms,which undergo the transformation of low temperature orthogonal phase to high temperature three oblique phase during the process of high and low temperature transformation.In this paper,the structure of tantalum oxide-based electrolyte is analyzed and found that the high temperature trioclinic phase can be stabilized to room temperature by doping.Based on the crystal struvture,we suppose that the co-doped tantalum-based electrolyte has two oxygen ion transport channels in its structure,which increases the oxygen ion transport efficiency and thus improves the conductivity.At the same time,it is found that the conductivity of the electrolyte is related to the oxygen vacancy concentration in its structure,and the increase of oxygen vacancy concentration in the electrolyte structure is beneficial to the transport of oxygen ions.The preparation and performance test of single-cell fuel cell based on co-doped tantalum oxide electrolyte Ta0.89Ti0.077Cr0.033O2.5-δwere carried out in this paper.The cathode and anode（symmetric electrodes）are made of20mol%Nb2O5 doped Sn O2 based low-expansion ceramic material,and the anode is nickel-catalyzed.The symmetrical single-cell prepared by the plate pressing method can effectively achieve the thermal matching between the components and the thin electrolyte layer,which meets the development requirements for reducing the operating temperature of fuel cells.It lays a foundation for further improvement of tantalum oxide-based electrolyte fuel cell. |
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