中溫型固態氧化物燃料電池陰極材料與金屬連接板之界面反應

Reaction at Interface between Cathode with Interconnect in Intermediate Temperature Solid Oxide Fuel Cells

周秉毅(Ping-Yi Chou)

指導教授 ： 洪逸明

元智大學/工程學院/化學工程與材料科學學系/碩士(2011年)

https://doi.org/10.6838/YZU.2011.00146

摘要

本論文研究之目的為探討中溫型固態氧化物燃料電池陰極與金屬連接板之界面反應。當金屬連接板經高溫熱處理後，會形成大量高阻抗且低導電率之氧化鉻，其部分將侵入並毒化陰極材料，造成材料之比表面積阻抗上升、氧離子催化能力下降以及導電率降低等問題，嚴重降低單電池之性能。因此，塗佈保護層防止鉻毒化陰極材料，並減少固態及氣態之氧化鉻產生，維持陰極電化學性質，為本實驗研究方向。
實驗中採用鐵基不繡鋼Crofer22 H與SUS 444作為金屬連接板。並利用 Citrate-EDTA法製備陰極材料La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF)及保護層材料LaxSr1-xCo0.5Mn0.5O3-δ，其中LaxSr1-xCo0.5Mn0.5O3-δ以x＝0.1、0.2及0.3作為測試。利用網印塗佈方式，分別將x＝0.1?0.3之材料塗佈於Crofer22 H上，經800 oC熱處理100小時後，使用X光繞射(X-ray Diffraction, XRD)鑑定，生成之氧化物以SrCrO3、LaCrO4及Mn1.5CrO4為主，其電性質遠優於Cr2O3等高阻抗氧化物。再以能量散射光譜儀(Energy Dispersive Spectrometer, EDS)作元素分佈分析後發現，以保護層La0.1Sr0.9Co0.5Mn0.5O3-δ抗鉻毒化效能最佳，並大量減少元素鉻往陰極方向擴散，配合X光繞射圖作分析，其生成之氧化物以SrCrO3為主。此外，將樣品在800 oC下，作100小時之比表面積阻抗(Area Specific Resistance, ASR)測試，La0.1Sr0.9Co0.5Mn0.5O3-δ之阻抗值約為5 mΩ．cm2 ；而La0.2Sr0.8Co0.5Mn0.5O3-δ及La0.3Sr0.7Co0.5Mn0.5O3-δ之阻抗值分別為15?40 mΩ．cm2及60?110 mΩ．cm2。綜觀各性質，以La0.1Sr0.9Co0.5Mn0.5O3-δ擁有最佳性能，因此選定以La0.1Sr0.9Co0.5Mn0.5O3-δ (LSCM)作為保護層材料。
選定保護層後，以網印將陰極材料LSCF塗佈於LSCM卅Crofer22 H及LSCM卅SUS 444，經 800 oC熱處理100小時後，作SEM、EDS及ASR測試分析，發現具LSCM塗佈之樣品，Cr擴散量遠低於未塗佈LSCM之樣品；於ASR方面，LSCF卅LSCM卅Crofer22 H及LSCF卅LSCM卅SUS 444樣品之最大及最小阻抗值為40 mΩ．cm2與17 mΩ．cm2以及42 mΩ．cm2與26 mΩ．cm2，明顯優於LSCF卅Crofer22 H及LSCF卅SUS 444的最大及最小阻抗值105 mΩ．cm2及60.23 mΩ．cm2 與 60 mΩ．cm2及25 mΩ．cm2。而經上述比較分析後，可發現塗佈LSCM之陰極，各性質皆遠優於未塗佈LSCM之樣品，因此，可證明La0.1Sr0.9Co0.5Mn0.5O3-δ為一優良保護層材料。
另外，本研究亦探討鉻毒化陰極之機制，以導電率 (Conductivity)及交流阻抗(AC Impedance)測試毒化對電子導性及氧離子導性之影響，發現受LSCM保護之陰極，經800 oC熱處理100小時後，導電率及氧離子傳導阻抗皆明顯優於未受LSCM保護之樣品。因此，為探討其毒化機制及原因，實驗中以低掠角XRD及EDS鑑定LSCF卅LSCM卅金屬連接板及LSCF卅金屬連接板間，各界面之氧化物，發現塗佈保護層之樣品，未生成Cr3O4及(Mn0.98Fe0.02)(Mn0.02Fe0.48Cr1.5)O4等高阻抗氧化物，且於LSCM卅金屬連接板界面處，未存在鐵鏽之主成分(Fe,Cr)2O3，此將利於維持較低之氧離子傳導阻抗以及較高之電子導性，不僅有助於維持陰極良好之電化學性質，於SOFC長時間運作時，效能可因此提升。

關鍵字

固態氧化物燃料電池 ； 金屬連接板 ； 鉻毒化 ； 保護層材料

並列摘要

The purpose of this study is to investigate the development of the interfacial reaction between the different chemical compositions of protective layer (LaxSr1-xCo0.5Mn0.5O3-δ, LSCM) with (Crofer22 H) metal interconnect and LSCM protective coating layer with interconnect (Crofer22 H and SUS 444). In addition, the mechanism of Cr poisoning on electrochemical properties of La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) cathode was reported. The LSCM protective layer were load on the surface of Crofer22 H by screen printing. After heat treatment , the chromium in Crofer22 H would migrate outward to form chromia which decreasing the electrochemical character of SOFCs.
Crofer22 H is a potential metal interconnect for intermediate-temperature solid oxide fuel cell (IT-SOFC), because it has excellent conductivity in the operation temperature range even for a long term. However, the Cr will diffuse to cathode to form C2O3, CrO3 and CrO2(OH)2 etc. to poison the oxygen reduction of cathode electrode. The purpose of this study is to investigate the interfacial reaction between LaxSr1-xCo0.5Mn0.5O3-δ (x= 0.1~0.3, LSCM) with Crofer22 H metal interconnect. The LSCM layers were coated on Crofer22 H by screen printing, and be heat-treated at 800 oC for 100 h. From the result of XRD and EDS, it was found the composition of SrCrO3, LaCrO4 and Mn1.5CrO4. The Cr can be prohibited to diffuse to cathode, especially for the La0.1Sr0.9Co0.5Mn0.5O3-δ layer, to prevent the cathode poison by Cr. The Area Specific resistance (ASR) of La0.1Sr0.9Co0.5Mn0.5O3-δ/ Crofer22 H is about 5 mΩ．cm2, which is much lower than total of La0.2Sr0.8Co0.5Mn0.5O3-δ/ Crofer22 H and La0.3Sr0.7Co0.5Mn0.5O3-δ/ Crofer22 H samples.
The conductivity and resistivity of LSCF cathode respectively contacted with Crofer22 H and LSCM/Crofer22 H were investigated. It was found that the amount of Cr3O4 and (Fe,Cr)2O3 formed in the LSCF/ Crofer22 H, which is not detect in LSCF/ LSCM/ Crofer22 H. A large amount of good conductivity compound SrCrO3 was found in the LSCF/ LSCM/ Crofer22 H, therefore, the area specific resistance (ASR) of LSCF/ LSCM/ Crofer22 H interconnect is only 17~40 mΩ．cm2 after heat treatment at 800 oC for 100 hours. The conductivity and resistivity of LSCF respectively are after reacting with LSCM/ Crofer22 H at 800 oC for 100 hours that are much better than that of LSCF cathode reacted with Crofer22 H. It is expect that LSCM is a potential protective layer for Crofer22 H interconnect with low ASR and effectively prevent Cr poison LSCF cathode.
Besides, another metal interconnect SUS 444 which was also explored by coating cathode LSCF with/ without LSCM protective coating layer. It was found that the amount of Cr1.3Fe0.7O3 and FeCrO4 formed in the interfacial layer of LSCF/ SUS 444, which is not detect in LSCF/ LSCM/ SUS 444. It was also found a large amount of SrCrO3 in the LSCF/ LSCM/ SUS 444. therefore, the ASR of LSCF/ LSCM/ SUS 444 is only 26~47 mΩ．cm2 after heat treatment at 800 oC, and it is lower than LSCF/ SUS 444 for 100 hours. The conductivity and resistivity of LSCF respectively are after reacting with LSCM/ SUS 444 at 800 oC for 100 hours which are much better than that of LSCF reacted with SUS 444.
Consequently, the protective coating layer LSCM is a potential protective layer not only for Crofer22 H, but SUS 444. However, it could prevent Cr to poison cathode effectively, and always maintain low ASR, resistivity and high conductivity when SOFC operating for a long term.

並列關鍵字

SOFC ； Interconnect ； Chromium poison ； Protective layer

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