| 摘要: | 儘管固體氧化物燃料電池（SOFCs）具有高效率、環保和燃料靈活性等重要優勢，但其較高的操作溫度（>800 ⁰C）通常導致快速的熱降解，限制了其商業應用。基於質子傳導電解質的SOFCs（稱為P-SOFC）近幾十年來受到關注，因為質子傳導具有比氧離子傳導更低的活化能，使得操作溫度能夠降低（400-800 ⁰C）。然而，P-SOFC的性能仍然受到限制，因為在較低的操作溫度下，極化電阻成為速率限制步驟，這是由於陰極氧還原反應（ORR）的遲滯性。在P-SOFCs中應用鈣鈦礦混合離子-電子導體（MIEC）La0.6Sr0.4Co0.2Fe0.8O3-δ（LSCF）陰極會將水形成位點限制在電解質/陰極界面相鄰的三相界面，從而限制電流密度。因此，急需開發具有更高電荷傳輸和轉移速率的陰極材料，以提高在中溫下操作的燃料電池的功率密度。
作為質子固體氧化物燃料電池（P-SOFCs）最有前景的陰極材料，具有三重導電性（e-/H+/O2-）的氧化物已被廣泛研究，因為它們在較低的操作溫度下具有優異的催化活性。然而，直接通過刷塗或網印來應用這些陰極材料，與下層電解質層的接觸面積有限，導致陰極歐姆電阻和極化電阻較高。在本文的第一部分中，演示了透過脈沖激光沉積（PLD）發生自發相分離，可以生長出具有混合異質結構，約5納米寬的Gd0.3Ca2.7Co3.82Cu0.18O9-δ（GCCCO）-BaCe0.6Zr0.2Y0.2O3-δ（BCZY）層。這種納米複合層位於旋轉塗佈的BCZY電解質和刷塗的GCCCO陰極之間，可以有效增加兩個不同相之間的界面面積，促進質子在界面上的傳輸。這種電極設計將歐姆電阻降低了0.35 Ω cm2，極化電阻降低了三倍，因此顯著提高了電池性能。隨後發現，在實施異質界面後，性能的提升有限的原因歸因於底層半電池存在問題。因此，在具有相同BCZY緩衝層、GCCCO-BCZY納米複合層和GCCCO陰極層的燃料電池上進行了對商業化的BCZYYb基半電池的測試。結果表明，在700 ⁰C時，峰值功率密度增加了一倍以上，達到863 mW/cm2，歐姆電阻在700 ⁰C時急劇降低到0.7 Ω cm2，是原來的五分之二。這證實了在使用PLD沉積的GCCCO-BCZY納米複合陰極界面時，具有GCCCO陰極的電池的電阻和峰值功率密度的瓶頸轉移到陽極和/或電解質，突顯了這種陰極結構的高性能。
在本論文的第二部分中，通過優化燃料電極的微觀結構，完成了對內部基板的改進。由於陽極支撐是燃料電池中最厚（約1mm）的部分，其微觀結構可以在一定程度上影響陽極支撐的質子陶瓷燃料電池（PSOFCs）的電化學性能。這是因為燃料電極中的孔徑大小及其分佈與與燃料相關的質量傳輸阻力密切相關，影響其能夠達到用於氫氧化反應的電化學活性位點之能力。
因此，我們報告了使用無灰紙纖維作為P-SOFCs氫電極的造孔劑的可行性研究，展示了其獨特的微觀結構--具有大規模連接的圓柱形孔洞，可以增強燃料的運輸效率。一個含有20 wt %紙纖維的Ni-BaCe0.7Zr0.1Y0.1Yb0.1陽極基板實現了37.97 vol%的孔隙率，相比使用30 wt%馬鈴薯澱粉造孔劑（29.12 vol%）具有更低的含量。隨後，通過電泳沉積對孔填充層表面進行改性，使用脈沖激光沉積（PLD）實現了在大孔洞陽極基板上的陶瓷功能層和中間層的薄膜沉積。
一個含有20 wt %紙纖維的陽極支撐單電池在600 ⁰C時展現了最佳的電化學性能，其峰值功率密度為550 mW/cm2，歐姆電阻為0.678 Ωcm2，極化電阻為0.172 Ωcm2，相比之下，使用30 wt %澱粉造孔劑的電池為電化學性能，其峰值功率密度為389 mW/cm2，歐姆電阻為0.802 Ωcm2，極化電阻為0.252 Ωcm2。這些發現強調了紙纖維作為氫電極造孔劑的效能，凸顯了在中溫下改進PSOFC性能的潛力。
;Despite the significant advantages of solid oxide fuel cells (SOFCs) such as high efficiency, environment friendliness, and fuel flexibility their high operation temperatures (>800 ⁰C) often result in fast thermal degradation, which limits their commercialization. SOFCs based on proton-conducting electrolyte (termed P-SOFC) has drawn much attention in the last few decades, because proton conduction has a substantially lower activation energy compared to that of oxygen ion conduction, rendering the possibility of a lowered operation temperature (400-800 ⁰C). However, the performance of P-SOFC is still limited, because at lower operation temperatures polarization resistance become the rate-limiting step due to the sluggish nature of oxygen reduction reaction (ORR) at the cathode side. Application of a mixed ionic-electronic conductor (MIEC) perovskite oxide La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode in P-SOFCs can restrict the water formation site to three-phase boundaries adjacent to the electrolyte/cathode interface, thereby limiting the current density. Thus, the development of cathode materials with higher charge transport and transfer rates is urgently needed for raising the power density of a fuel cell operated at intermediate temperatures.
The triple-conducting (e-/H+/O2-) oxides have been extensively studied as the most promising cathode materials for protonic solid oxide fuel cells (P-SOFCs) because of their excellent catalytic activity at lower operating temperatures. However, direct application of these cathode materials by brush-painting or screen-printing provides limited contact area with the underlying electrolyte layer, resulting in high cathode ohmic and polarization resistances. In the first section of this dissertation, it is demonstrated that a bulk heterojunction Gd0.3Ca2.7Co3.82Cu0.18O9-δ (GCCCO)-BaCe0.6Zr0.2Y0.2O3-δ (BCZY) layer with a domain width of ~5 nm can be grown by pulsed laser deposition (PLD) via spontaneous phase separation. Such a nanocomposite interlayer between spin-coated BCZY electrolyte and brush-painted GCCCO cathode can effectively increases the interfacial area between the two distinct phases and facilitates proton transport across the interface. This electrode design reduces the ohmic resistance by 0.35 Ω cm2 and the polarization resistance by a factor of three, thus significantly boosting the cell performance. Later it is identified that the limited performance enhancement after the implementation of bulk heterojunction interlayer, is attributed to issues in the underlying half-cell. Therefore, a fuel cell with same BCZY buffer layer, GCCCO-BCZY nanocomposite interlayer, and GCCCO cathode layer is tested on a commercial BCZYYb-based half-cell. Results show a more than twofold increase in power density, reaching 863 mW/cm2 at 700 ⁰C, and a dramatic 2.5-fold decrease in ohmic resistance to 0.7 Ω cm2 at 700 ⁰C. This confirms that the bottle neck in cell resistance and peak power density, with the GCCCO cathode, shifts to the anode and/or electrolyte when using a PLD-deposited GCCCO-BCZY nanocomposite cathode interlayer, highlighting the high performance of this cathode structure.
In the second section of this dissertation, the improvement of in-house substrate is accomplished by optimizing the microstructure of the fuel electrode. Since the anode support is the thickest (~1mm) part in the fuel cell, its microstructure can influence the electrochemical performance of an anode supported protonic ceramic fuel cell (PSOFCs) to a certain extent, due to the fact that the pore size and its distribution in the fuel electrode are closely linked to the mass transport resistance associated with the fuel, impacting its ability to reach the electrochemically active sites available for the hydrogen oxidation reaction. Therefore, we report our findings about the feasibility of using ashless paper-fibers as a pore former for the hydrogen electrode of P-SOFCs, demonstrating its unique microstructure with large interconnected cylindrical pores that enhance fuel transport efficiency. A Ni-BaCe0.7Zr0.1Y0.1Yb0.1 anode substrate with 20 wt % paper fibers achieve a porosity of 37.97 vol% with a lower content of paper fibers, as compared to using 30 wt% potato starch porogen (29.12 vol%). Subsequently, the thin film deposition of ceramic functional layers and interlayers on a macro-porous anode substrate is achieved using pulsed laser deposition (PLD), facilitated by its surface modification through electrophoretic deposition of a pore filler layer. An anode supported single cell with 20 wt % paper fibers exhibit the best electrochemical performance at 600 ⁰C with a peak power density of 550 mW/cm2, ohmic resistance of 0.678 Ωcm2, and a polarization resistance of 0.172 Ωcm2 as compared to the cell with 30 wt % starch porogen (389 mW/cm2, 0.802 Ωcm2, and 0.252 Ωcm2). These findings underscores the efficacy of paper fibers as a pore former for tailoring the microstructure of the hydrogen electrode, highlighting the potential for improved PSOFC performance at intermediate temperatures. |
