The Preparation and Chemical Characteristic of Bi0.85-xCa0.15ZrxO1.5-δ Solid Oxide Fuel Cell Electrolyte

• Main Authors: Yu-Ting Chiu, 邱郁庭
• Other Authors: I-Ming Hung
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/ba4y5c

碩士 === 元智大學 === 化學工程與材料科學學系 === 102 === In this study, Ca and Zr doped Bi2O3 composite electrolyte was synthesized by the solid state reaction method to stabilize the cubic phase Bi2O3 ceramics. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS) and the temperature-programmed reduction (TPR). XRD data showed that in the stoichiometric ratio of range 0.12 ≤ x ≤ 0.24, all of the Bi0.85-xCa0.15ZrxO1.5-δ samples had cubic fluorite structure. The lattice parameters were found in the range of 5.512～5.525 #westeur006#. The highest value of conductivity was 0.05 S/cm at 750 oC for x= 0.15. The Arrhenius plots of the Bi0.85-xCa0.15ZrxO1.5-δ samples showed that there was a change in conductivity activation energy at the temperature of 550 oC. The typical impedance spectra for Bi0.85-xCa0.15ZrxO1.5-δ samples showed that all resistances were decreased when the temperature increased. The main resistance was electrode polarization resistance at 600 oC, however, the main resistance was ohmic resistance at 750 oC. All the grain size conductivities were higher than grain boundary conductivities because the second phase existed on grain boundary region. The coefficient of thermal expansion(CTE) varied from 12.1 #westeur024# 10-6 K-1 to 15.0 #westeur024# 10-6 K-1 in the temperature range from 300 to 600 oC. Compared with YSZ, Bi0.85-xCa0.15ZrxO1.5-δ had better matching CTE with the cathode materials. The temperature-programmed reduction (TPR) showed that oxygen released below 400 oC but the operating temperature for LT-SOFC is from 500 to 750 oC. For the bismuth oxide system electrolyte, how to avoid Bi2O3 reducing Bi is still a problem need to be overcome. At the stability test, the phase of Bi0.85-xCa0.15ZrxO1.5-δ samples changed from cubic to monoclinic. After annealed at 600 oC for 48 hours, the relative conductivity decreased below 0.1. From the SEM results, the second phase ratio increased. xBi0.67Ca0.15Zr0.18O1.5-δ - (1-x)Bi0.5Sr0.5MnO3- composite materials were formed with cubic and perovskite structure, and no chemical reaction between Bi0.67Ca0.15Zr0.18O1.5-δ and Bi0.5Sr0.5MnO3- materials. The highest value of conductivity was 88.34 S/cm for x= 0.3. From the cross-sectional micrographs of xBi0.67Ca0.15Zr0.18O1.5-δ - (1-x)Bi0.5Sr0.5MnO3- symmetric cell, the microstructure showed a porous character of the cathode layer. The typical impedance spectra for xBi0.67Ca0.15Zr0.18O1.5-δ - (1-x)Bi0.5Sr0.5MnO3- samples showed that all resistances were decreased when the temperature increased. The polarization resistance, Rp , had a lowest value of 0.345 Ω．cm2 at 750 oC for x= 0.3.