| 摘要: | 有效提高氧離子傳導型固態氧化物燃料電池(Oxygen-ion-conducting solid oxide fuel cell, O-SOFC)操作效能除了將電極結構最佳化外，最直接的途徑為大幅縮短離子於電解質之傳輸路徑以降低其歐姆阻抗，也就是將電解質層厚度縮減至薄膜尺度。目前製備固態電解質薄膜方法相當多元，如電子蒸鍍(E-beam evaporation)、射頻磁控濺鍍(RF magnetron sputter)、脈衝雷射沉積(Pulse laser deposition, PLD)、旋轉塗佈(Spin coating)與電漿噴塗(Plasma spraying) 等。其中旋轉塗佈法是將基板置於塗佈機圓盤中，利用幫浦抽氣將基板固定，藉由載台旋轉將電解質均勻塗佈在基板上。由於不需要在真空環境操作，並且薄膜可以大量快速的塗佈於基板上，材料及設備成本較低，適用於商業化大量生產。同時薄膜厚度可藉由基本參數控制，如轉速、懸濁液黏性、溶劑揮發等。而過去幾年許多研究團隊也已利用PLD技術製作薄膜型O-SOFC進行許多相關研究，雖薄膜型O-SOFC在操作溫度600 ℃以下仍有優異之性能表現，但因電解質與陰極界面之化學穩定性不佳，即使利用Ce1-xGdxO2-δ (GDC)作為YSZ/LSC界面緩衝層，經過電池封裝、升溫、還原與測試等步驟之測試時程過久，仍會導致二次相出現使電池性能大幅下降。文獻亦發現其他O-SOFC材料亦有元素熱擴散行為(Thermally-activated diffusion)導致二次相生成的現象發生；例如 LaSrGa3O7與NiO二次相生成於GDC/La1-xSrxGa1-yMgxO3-δ (LSGM)界面，且隨電池測試時間增長La擴散效應愈發顯著，因此陽極支撐型(Anode-supported) O-SOFC在長時間操作下極可能遇到上述等問題而導致性能衰退。另外，由於陽極的氫氧化反應(Hydrogen oxidation reaction, HOR)及陰極的氧還原反應(Oxygen reduction reaction, OOR)主要發生於陰、陽極三相點(Three phase boundary, TPB)，因此長時間操作下陰、陽極內部三相點的密度與分布變化也直接影響電池的整體效能。因此本計畫工作重點即藉由聚焦離子束(FIB)三維重構技術(3D reconstruction)及穿透式電子顯微鏡解析(TEM) ASC O-SOFC長時間衰退行為與其劣化機制。 ;In addition to optimizing the electrode structure, the most direct route to the effectively improve oxygen-ion-conducting solid oxide fuel cell (O-SOFC) efficiency is to significantly reduce the electrolyte transport path and this to reduce its Ohmic resistance, that is, the thickness of the electrolyte layer is reduced to a film scale. Up to now, the approaches for preparing a solid electrolyte membrane are quite multi-functional, such as E-beam evaporation, RF magnetron sputtering, pulse laser deposition (PLD), spin coating, and plasma spraying and so on. In the spin-coating method, the substrate is placed on the coater disk, the substrate is fixed by pump suction, and the electrolyte is uniformly coated on the substrate by the rotation of the stage. Due to the fact that it is not required to operate in a vacuum environment and that the film can be coated on a large-scale substrate quickly and with low materials and equipment costs, it is suitable for commercial mass production. At the same time, the thickness of the film can be well controlled by the basic parameters, such as speed, viscosity of the suspension, solvent evaporation. In recent years, many research groups have also conducted many researches on the fabrication of thin-film O-SOFCs by using PLD technology. Although thin-film O-SOFCs have excellent performance under the operating temperature of 600 ° C. Even with Ce1-xGdxO2-δ (GDC) as the YSZ / LSC interface buffer layer, the cell package, high-temperature sintering, reduction and testing steps such as the test time is too long, will lead to the formation of secondary phase and cause the cell performance drops significantly. The literature also found that other O-SOFC materials also have elemental thermally-activated diffusion, resulting in secondary phase formation; for example, LaSrGa3O7 and NiO secondary phase formed in GDC / La1-xSrxGa1-yMgxO3-δ (LSGM) interface and the La diffusion effect becomes more and more significant as the cell test time prolongs. Therefore, the anode-supported O-SOFC may encounter the above problems under prolonged operation, resulting in performance degradation. In addition, since the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction reaction (OOR) at the cathode mainly occur at the three phase boundary (TPB) of the anode and the cathode, the variation of the density and distribution of the three-phase points in the anodes and anodes also directly affects the overall performance of the battery after long-time operation. Therefore, the focus of the project is to analyze the long-term degradation behavior and degradation mechanism of ASC O-SOFC by focused ion beam (FIB) 3D reconstruction and transmission electron microscopy. |
