中低溫固態氧化物燃料電池電解質傳導機制探討與高性能電池開發;Transportation mechanism and high performance research for intermedium-low temperature solid oxide fuel cell electrolyte

NCUIR > Engineering College > Energy of Mechatronics > Electronic Thesis & Dissertation > Item 987654321/81896

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/81896

Title:	中低溫固態氧化物燃料電池電解質傳導機制探討與高性能電池開發;Transportation mechanism and high performance research for intermedium-low temperature solid oxide fuel cell electrolyte
Authors:	莊哲瑋;Jhuang, Jhe-Wei
Contributors:	能源工程研究所
Keywords:	固態氧化物燃料電池;質子傳導性電解質;鈣鈦礦結構;離子導電性;晶體結構;單層燃料電池;Solid oxide fuel cell;Proton-conducting electrolyte;Perovskite structure;Ionic conductivity;Crystal structure;Single layer fuel cell
Date:	2019-11-13
Issue Date:	2020-01-07 14:30:51 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究中，第一部分鎖定傳統之固態氧化物燃料電池電解質改質，進而強化電解質之化學穩定性，以展現固態氧化物燃料電池燃料選擇性廣之優點。故於此部分，本研究設計新式抗毒化手法，並進行毒化前後之相鑑定、導電度量測及碳酸鋇生成位置鑑定，進而了解相穩定性、表面毒化覆蓋狀況與電解質導電性之關聯性。另外，與藉由摻雜鋯來提升電解質化學穩定性之手法進行比較，分析不同抗毒化手法之效果。由研究結果顯示，此新式保護法，氧化鈰(Cerium oxide, CeO2)保護法，是藉由1600 oC高溫燒結之固態反應法，使電解質表面自然生成CeO2，為電解質提供保護作用，抑制二氧化碳毒化反應發生，並維持電解質表面離子通道，進而維持電池電化學性能。由電解質導電性毒化前後之比對結果也可發現，無CeO2保護法之鋇鈰釔氧化物電解質經二氧化碳毒化後，導電度衰退率高達56%，而有CeO2保護法之鋇鈰釔氧化物電解質經二氧化碳毒化後，導電度衰退率僅有7%，說明CeO2於電解質表面能有效防止導電度之衰退。另外也配合相穩定性研究(XRD)及毒化物與表面生成位置分析(拉曼光譜mapping)之結果可發現，為維持電解質性能不受二氧化碳毒化所影響，除維持鈣鈦礦結構之相穩定性外，保護表面質子傳導路徑不受非離子導體之碳酸鋇阻絕也為重要的因素之一。第二部分研究，主要探討材料之晶體結構對電解質質子導電性之影響，進而做為未來材料改質優化之依據。由研究結果可知，材料可藉由不同量測氣氛，分析材料不同之離子傳導性。而不同離子傳導性則會受不同因素影響，如鋇鈰氧化物於空氣下之導電性主要受到氧離子傳導性之影響，故隨著鋯摻雜比例提升，會造成樣品晶粒變小，導致晶界阻抗上升使導電性下降。而氫氣下之質子導性則較為複雜，會受自由體積與載子濃度等因素影響，需藉由準確判斷材料之晶體結構、自由體積、載子濃度與遷移率才能分析材料質子傳導性，而此部分成功將EBSD應用於鈣鈦礦結構陶瓷材料晶體結構鑑定，成功分析不同鋯摻雜比例之樣品晶體結構，進而計算其晶體常數、自由體積等數值，並將晶體相關參數結果與質子導電性結果做連結。最後單層燃料電池之設計成功於本研究應用，單層燃料電池為一將燃料電池陽極/陰極/電解質功能混合成單一中間層材料之燃料電池，藉由三合一混合的效果，免去電極與電解質層中間之異質介面，並縮短離子傳遞距離，進而使電池性能大幅上升。另外，中間層(混合陽極/陰極/電解質功能之材料)也鎳發泡材於雙邊固定，提供電池機械強度，並製作肖特基結，防止電子短路現象發生。最後本研究設計同時擁有三傳導性(電子/氧離子/質子)材料(鋇鈷鐵鋯釔氧化物, BaCo0.4Fe0.4Zr0.1Y0.1O3)，作為單層燃料電池之中間層材料，藉由整合單層燃料電池與三傳導性材料之特，進而大幅增加燃料電池反應面積，提升單層燃料電池性能，並藉由三導體材料混合不同離子導體，調整中間層材料之導電性，成功製備於低溫下擁有高性能之燃料電池(於0.6 V 550 oC時之電流密度提升至1.2 A/cm2)。 ;This first part of study investigated the decline in the conductivity and mechanical strength after CO2 poisoning and found a new protective method for BaZrxCe0.8-xY0.2O3 (BCZY) proton-conducting electrolyte. The high temperature solid state reaction (SSR) was used in synthesizing electrolyte to naturally generate CeO2 on the surface. A comparison of the oxides in the conductivity decline test revealed that the sample with CeO2 on the surface substantially improved the stability of conductivity, reducing the decline ratio from 56% to 7% for BCY and 50% to 7% for BCZY. Raman mapping results indicate the naturally generated CeO2 on electrolyte surface can considerably reduce impurity formation and maintain the microstructure of electrolyte. This work demonstrates that samples with CeO2 on the surface effectively protect the BaCeO3-based proton-conducting electrolyte from CO2 poisoning. This method may be applied to similar BaCeO3-based perovskite materials as a new protective method. The second part of study, we vary the Ce to Zr ratio to investigate the microstructure and electrical property of zirconium doped barium cerate. The solid state reaction is used in synthesizing the BaCe0.8-xZrxY0.2O3 (BCZY0.1~0.5, x= 0.1~0.5). The electron backscatter diffraction (EBSD) is successfully applied to identify the crystal structure of barium cerate. EBSD results indicate that all samples maintain orthorhombic structure. Conductivity measurement results show that for temperatures below 700 oC, Zr-doped barium cerate has higher proton conductivity than oxygen ion conductivity. The protonic conductivity increases with the Zr ratio initially, but decreases after the Zr ratio is higher than 0.3. For stable operation in CO2 atmosphere, Zr ratio of barium cerates should be greater than 0.2. The last part of study, we build up the single layer fuel cell (SLFC). The BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY0.1) is be chosen as SLFC electrolyte materials in this study. Because BCFZY has been discovered as “triple conducting” cathode material, i.e. simultaneous proton, oxygen-ion and electron-hole conductivity. In comparison to the conventional mixed oxide ion and electron/hole conducting cathode, the triple-conducting BCFZY0.1 cathode may eliminate the three-phase-boundary constraints, which makes the entire cathode electrochemically active and be suitable for low temperatures SLFC. Additionally, the SLFC based on the Schottky type using perovskite BCFZY0.1 material is mixed with BaCe0.8Y0.2O3-δ (BCY) and Sm0.15Ce0.85O2-δ-Na2CO3 (NSDC) to modify electronic and ionic conductivities. Finally, the high performance SLFC have been found as 80% BCFZY mixing with 20% BZY (BCFZY0.1+20BZY). The BCFZY0.1+20BZY reach 1.2 A/cm2@0.6 V at 550 oC.
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