| Energy saving,emission reduction and green living are the major trends in our time.Solid Oxide Fuel Cell（SOFC）is a high-output power device that utilize clean gases as fuel and provide safe and environmentally friendly power output.Bi2O3 is a polycrystalline electrolyte material that plays a crucial role in conducting oxygen ions and isolating fuel gas in SOFC.The face-centered cubic phase of Bi2O3 possesses 25%oxygen vacancies and exhibits the highest electrical conductivity,but this structure only exists in pure Bi2O3 above 730℃.The temperature range of the high conductivity phase can be broadened and stabilized to room temperature using elemental doping.Therefore,studying the electrical properties of doped Bi2O3-based electrolyte materials is in line with the direction of low temperature development in SOFC.In this paper,we aimed to synthesize double-doped and triple-doped Bi2O3-based electrolyte materials using the nitrate combustion method at various calcination temperatures,and to modify them with doping to stabilize the cubic fluorite structure that possesses high electrical conductivity at room temperature.The sintered electrolyte’s microscopic morphology was analyzed and studied using X-ray diffraction;the electrolyte materials’thermal stability was analyzed using thermogravimetry;and the ionic conductivity and long-term stability of the electrolyte materials were tested using the AC impedance method.The main results of our study are as follows:(YO1.5)x（MoO3）0.05(ErO1.5)y(BiO1.5)0.95-x-y（x=0.05,0.10,0.15,0.20 and y=0.05,0.10,0.15,0.20）all have pure phases with face-centered cubic structure after sintering for 10 h.The increase in the total doping leads to the cell shrinkage.The SEM results showed that the grain size tended to decrease with increasing doping concentration,with the sample Y20Mo5Er5 exhibiting the smallest grain size.Among all samples,Y20Mo5Er5 exhibited the highest electrical properties,reaching 16×10-2S/cm at800℃.Additionally,Y20Mo5Er5 exhibits good thermal stability and high density（95.39%）,satisfying the requirements of SOFC.The(HoO1.5)x(SmO1.5)y(Bi O1.5)1-x-y（x=0.02,0.04,0.05,0.06,0.10,0.15 and y=0.03,0.05,0.06,0.10,0.15）electrolyte materials were prepared by nitrate combustion method.The XRD results show that Bi2O3-based solid solution with a single cubic fluorite structure in the range of 0.10≤x≤0.15,0.05≤y≤0.10,x=0.06,y=0.03 and x=0.05,y=0.05.AC impedance tests showed that the conductivity of Ho5Sm5 tended to increase and then decrease with the increase of total doping.In the Arrhenius curves of all cubic phase samples,the slope changed at 600℃.The Ho5Sm5 sample exhibited the lowest low and high temperature activation energies among all samples,indicating a simpler energy acquisition process and improved ion mobility.The conductivity of Ho5Sm5 sample reached 14.18×10-2S/cm at 800℃.The electrical properties of Ho5Sm5 were stable during a 50-hour aging test at a constant temperature of 500℃.In the(HoO1.5)x(NdO1.5)y(BiO1.5)1-x-y（x=0.02、0.04、0.05、0.06、0.10、0.15 and y=0.03、0.05、0.06、0.10、0.15）system,samples with pure cubic fluorite structure were detected in the range of 0.05≤x≤0.15,y=0.05 and x=0.15,y=0.10.The diffraction peaks of Ho5Nd5 were higher and sharper,indicating the sample has good crystallinity.The distribution of grain size ranges from 0.3 to 2.4μm when the total doping concentration reaches 25%.there is only one impedance arc in the impedance diagram of Ho5Nd5 at 400～800℃.With the increase of temperature,the impedance arc with the left end of the real axis gradually moves toward the high frequency.In the aging test,the electrical properties of Ho5Nd5 showed almost no degradation within 50 h.Compared with the data of the Ho-Sm-Bi system,Ho5Nd5 possesses higher high electrical properties with a conductivity of 16.29×10-2S/cm at 800℃,and shows great potential as an electrolyte material. |
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