利用溶膠凝膠法合成製備燒結促進劑摻雜於氧化釓摻雜氧化鈰電解質之材料特性與電性能研究

Materials Characteristics and Electric Performance of Gd2O3 doped CeO2 with the doping of Sintering Aids by Sol-Gel Methods

蘇昱銘(Yu-ming Su)

指導教授 ： 郭俞麟

大同大學/工程學院/材料工程學系所/碩士(2009年)

摘要

本研究將提出利用溶膠凝膠法摻雜氧化矽(SiOX)、氧化鈦(TiOX)並作為燒結促進劑(Sintering aids)於氧化釓摻雜氧化鈰(GDC)固態氧化物電解質，尋求達到降低燒結溫度，發展成為實用電解質材料改質之技術。製備後之粉體材料性質判定則以X光繞射儀(XRD)及比表面積分析儀(BET)分析其結晶結構及粉體尺寸與利用掃瞄式電子顯微鏡 (SEM)觀察其表面型態，密度及電性能則利用阿基米德法及交流阻抗分析儀來測量。
在氧化矽或氧化鈦摻雜於GDC電解質系統之鍛燒製程，顯示氧化矽或氧化鈦摻雜濃度為0~3.0 wt.%時之電解質粉末無第二相的產生。XRD結果顯示隨著氧化矽或氧化鈦摻雜濃度增加，其晶格常數會隨之減少，主要是由於矽離子或鈦離子其離子半徑小於釓離子及鈰離子所導致。從XRD及BET之分析， DBET及DXRD之數值顯示其晶粒尺寸及顆粒尺寸會隨著氧化矽或氧化鈦摻雜濃度增加而隨之減少，其晶粒尺寸及顆粒尺寸範圍在20~45 nm之間。TGA及DTA結果顯示無明顯的重量變化，且為穩定之相結構。從SEM結果顯示，當氧化矽或氧化鈦摻雜濃度高於1 wt.%時，其粉體會有團聚之現象產生。
在氧化矽或氧化鈦摻雜於GDC電解質系統之燒結製程，XRD結果顯示氧化矽或氧化鈦摻雜濃度為0~3.0 wt.%時無第二相產生。由SEM分析及阿基米德法得知，氧化矽或氧化鈦摻雜濃度為0.25~0.5 wt.%可減少燒節溫度及提高相對密度。從相對密度比較來看，在燒結溫度1500 ℃，持溫5小時之未摻雜的GDC電解質其相對密度約為91.99 %，而氧化矽或氧化鈦摻雜濃度為0.25 wt.%之GDC電解質其相對密度分別為91.21 %、92.01 %。此結果顯示，摻雜微量的燒結促進劑於電解質仍保有相當程度之緻密性。
在電性能方面，摻雜微量的氧化矽或氧化鈦於GDC電解質比起未摻雜的GDC電解質具有較高之導電性。當燒結溫度為1400 ℃，持溫5小時，在氧化矽或氧化鈦摻雜濃度為0.25 wt.%時，具有較高之導電性分別為2.84×10-2 S/cm及5.12×10-2 S/cm (量測溫度為800 ℃)，其值高於未摻雜的GDC電解質之2.65×10-2 S/cm (量測溫度為800 ℃)。
本研究結果顯示添加燒結促進劑於GDC電解質中能降低固態氧化物電解質緻密過程中所需之燒結溫度，且摻雜微量的燒結促進劑可提高其相對密度，其導電性比起傳統的YSZ較適合做為固態氧化物燃料電池之電解質。

關鍵字

固態氧化物燃料電池 ； 溶膠凝膠法 ； 氧化釓摻雜氧化鈰

並列摘要

In this study, we proposed sol-gel method to prepare gadolinia-doped ceria (GDC) solid electrolytes with the addition of SiOX or TiOX as the sintering aids. Materials characteristics of the prepared and calcined electrolyte samples were identified by X-ray diffraction (XRD) for crystalline structure, Specific surface area analyzer (BET) for particle size and scanning electron microscopy (SEM) for surface morphology of powders. The electric performance and density were measured by Archimedes method and AC impedance method.
For the calcined process of SiOX-doped or TiOx-doped GDC systems, the results showed that the prepared electrolyte powder had no additional impurity phases as the dopant concentrations of SiOX or TiOx were 0~3.0 wt.%. XRD results indicated lattice constants of prepared powder decreased as the dopant concentrations of SiOX or TiOx increased, because Si4+ or Ti4+ has smaller ionic radius than Gd3+ and Ce4+. For XRD and BET analyses, DBET and DXRD values showed particle sizes and crystallite sizes decreased as the dopant concentrations of SiOX or TiOx increased. The ranges of particle sizes and crystallite sizes were 22~55 nm and 20~45 nm. TGA and DTA spectra showed no obvious weight loss, and had a stable phase structure at higher temperatures (900°C). From SEM results, the agglomeration behavior of electrolyte powders for excessive SiOX-doped or TiOx-doped concentration (> 1 wt.% ) was obviously observed.
For the sintered process of SiOX-doped or TiOx-doped GDC systems, the sintered sample without additional impurity phases were obtained as the dopant concentrations of SiOX or TiOX were 0~3.0 wt.%. By SEM analysis and Archimedes method, doped 0.25~0.5 wt.% SiOX or TiOX could reduced the sintering temperature and increased the relative density. The relative density of undoped GDC pellet under the sintering process of 1500 °C and 5 hours was around 91.99 %, while the relative density of 0.25 wt.% SiOX-doped or TiOX-doped GDC pellets under the sintering process of 1400 °C and 5 hours were 91.21 % and 92.01 %. The results showed that the electrolyte with small doped concentration of SiOX or TiOX could achieve to a higher densification of electrolytes for solid oxide fuel cells (SOFCs).
For the electric characteristic, the small concentration of SiOX-doped or TiOx-doped GDC pellets had the higher conductivity than pure GDC pellets. As sintering at 1400 °C for 5 hours, the highest total conductivities were obtained in 0.25 wt.% SiOX-doped GDC pellet with σ800 °C = 2.84×10-2 S/cm and 0.25 wt.% TiOX-doped GDC pellet with σ800 °C = 5.12×10-2 S/cm, as compared to the undoped GDC with a total conductivity of 2.65×10-2 S/cm at 800 °C .
It could be concluded that the preparation of adding sintering aids in GDC electrolytes was successful to lower the sintering temperature of the densification for solid oxide electrolytes, and small concentration of sintering aids doped GDC pellets with the higher relative density and the comparable conductivity can be used as solid electrolyte layers for SOFCs system as compared to the well-known YSZ.

並列關鍵字

solid oxide fuel cells ； sol-gel method ； Gd2O3 doped CeO2

參考文獻

4. J. Larminie and A. Dicks, “Fuel Cell Systems Explained” Chichester, West Sussex : Wiley (2003) 2ed.

6. Chunshan Song, “Fuel processing for low-temperature and high-temperature fuel cells Challenges, and opportunities for sustainable development in the 21st century,” Catalysis Today 77 (2002) 17-49.

7. N. Q. Minh, “Ceramics Fuel Cells,” J. Am. Ceram. Soc., 76 (3) (1993) 563~588.

9. J. Mizusaki, H. Tagawa, Y. Miyaki, S. Yamauchi and K. Hirano, “Kinetics of The Electrode Reaction at the CO-CO2, Porous Pt/Stabilized Zirconia Interface,” Solid State Ion., 53 (1992) 126-134.

10. R. Peng, C. Xia, X. Liu, D. Peng, G. Meng, “Intermediate-temperature SOFCs with thin Ce0.8Y0.2O1.9 films prepared by screen-printing,” Solid State Ion., 152-153 (2002) 561-565.