研究生: |
黃健銘 Cheng-ming Huang |
---|---|
論文名稱: |
高導電活化電極應用於陽極支撐型固態氧化物燃料電池 Development of a highly ionic conductivity anode for an anode-supported Solid Oxide Fuel Cell design |
指導教授: |
周振嘉
Chen-Chia Chou |
口試委員: |
郭東昊
Dong-Hau Kuo 鄭逸琳 Yih-Lin Cheng |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 機械工程系 Department of Mechanical Engineering |
論文出版年: | 2009 |
畢業學年度: | 97 |
語文別: | 中文 |
論文頁數: | 107 |
中文關鍵詞: | 固態氧化物燃料電池 、陽極支撐 、活化陽極 |
外文關鍵詞: | Solid Oxide Fuel Cell, anode-supported, active layer |
相關次數: | 點閱:179 下載:3 |
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為了提升陽極支撐型固態氧化物燃料電池的陽極之催化活性與離子導電,40wt.%高離子導共摻雜釔穩定氧化鋯(Zr0.92Y0.155Mg0.005O2.0775,YMSZ)混合60wt.%氧化鎳開發之新型陽極Ni-Zr0.92Y0.155Mg0.005O2.0775 (Ni-YMSZ)置入於常用陽極與電解質之間當作活化陽極層以降低陽極極化阻抗。AC 阻抗圖譜技術用以檢視界面活性及陽極微觀所造成的信號,鐵弗曲線分析和功率密度測量分別用來觀察三相點之電化學反應與檢驗實際燃料電池轉換化學能為電能的效率。
本實驗利用刮刀成型手法製作電解質和陽極,並將陰極網印在電解質和陽極共燒之後的電解質表面。SEM顯示刮刀成型製備陽極支撐層、活化陽極層與電解質,網印之陰極在陽極支撐半電池(Ni-YSZ / Ni-YMSZ / YSZ / Pt-YSZ )共燒1350℃一小時,並於20%H2+80%N2溫度800℃持溫2小時下還原得到電解質緻密與電極多孔之要求,而白金陰極、電解質(YSZ)、活化陽極層(Ni-YMSZ)、陽極支撐層 (Ni/YSZ)之間接合良好,無分層或剝落現象。陽極陶瓷離子導體與金屬電子導體呈現均勻的網絡狀分布,顯示了良好的微觀形貌。
從交流阻抗圖中的極化電阻(Rp)結果指出,添加活化陽極層之陽極在800℃下擁有較低的極化電阻(0.69 ohm-cm2),較常用陽極能夠降低界面之極化損失,此結果解釋添加高離子導之活化陽極層,確實有降低電極在電解質與燃料間的極化損失。在相同氣氛(40%H2-60%N2)中分析鐵弗曲線,添加活化層的陽極在800℃之交換電流密度(0.038 A/cm2,log i0)值明顯較常用陽極要高。由此可知陽極添加活化層除了降低極化阻抗,更提升了電極對燃料氣氛下的催化能力。對照發現交換電流密度(log i0)與極化電阻(Rp)具有相依性,較低的極化損失讓帶電粒子(O2-與e-)在陽極與界面(陽極與電解質)容易傳遞,使得三相點催化能力提升,並釋放出更多電子。
本研究在40%H2+60%N2 流量100sccm的燃料氣氛,陽極支撐含活化層半電池 (Ni-YSZ / Ni-YMSZ / YSZ / Pt-YSZ )於800℃最大功率密度為98.49mW/cm2大於陽極支撐半電池(Ni-YSZ / YSZ / Pt-YSZ )之功率密度87.68 mW/cm2。而陽極支撐含活化層單電池陰極搭配LSCF-YSZ複合陰極 (Ni-YSZ / Ni-YMSZ / YSZ / LSCF-YSZ) 於800℃功率密度可提升至135.71mW/cm2,依然優於陽極支撐無活化層單電池(Ni-YSZ / YSZ / LSCF-YSZ )之功率密度110.73 mW/cm2。因此陽極支撐型電池若添加陽極活化層將可用來提高SOFC於高、中溫的工作效率。這個製程在未來可應用於多個單電池疊合成的電池堆( cell stack ) 的裝置來產生高功率輸出。
For enhancing the catalytic activity and ionic conductivity of anode, yttria and magnesium oxide co-doped zirconia electrolyte Zr0.92Y0.155Mg0.005O2.0775 modified with 60wt% nickel particle (Ni) was applied to be a active layer coating at the interface between Ni-YSZ traditional anode and YSZ electrolyte to decrease the polarization resistance. AC impedance spectroscopy technique was adopted to check interfacial property and anode structure, Tafel curve analysis was used to observe the performance of electrochemical reaction at the TPB’s and power density measurement was used to check the efficiency of the fuel cell in converting chemical energy into electrical energy.
Electrolyte and anode thick films were successfully fabricated using tape casting technique and co-firing of electrolyte and anode. Microstructure analysis using SEM pictures shows that the co-sintering of anode supported the half cell at 1350℃for 1h had a dense electrolyte and anode/anode active layer with uniform distribution of ionic conducting YSZ/YMSZ particles and catalytic Ni particles, sufficient porosity and homogeneous network structure. The interfacial property between different components of the half cell was improved significantly by using co-sintering electrolyte, anode, anode active layer, cathode.
Experimental results show that the polarization resistance of traditional anode, Ni-YSZ, was reduced from 1.79 Ω-cm2 to 0.69Ω-cm2 by adding a active layer, Ni-YMSZ, at 800℃, because of increasing the amount of triple phase boundary (TPB) and decreasing of activation energy of oxygen ion migration in YSZ was observed by modifying appropriate elements to YSZ. The catalytic activity of anode with an active layer correlated with the value of exchange current density (logi0) identified from Tafel plots under 40% H2 condition. The exchange current densities of anode with an active layer are higher than that of Ni-YSZ at 800oC. Therefore the catalytic activity of anode depends on the ionic conductivity of co-doping zirconia in anode with an active layer. Besides, it is found that there are some correlations between logi0 and Rp, increasing of exchange current density and decreasing of polarization loss were observed due to mass transfer of oxygen ion and charge transfer easy in anode with an active layer.
The efficiency of the half cell in converting the chemical energy in to electrical energy was estimated by measuring the power density using 40%H2+60%N2 (100 sccm) as fuel and air as oxidant. Anode-supported with an active layer half cell has shown the power density of 98.49 mW/cm2 at 800℃which is much higher than non active layer half cell of 87.68 mW/cm2. Power density of Single cell with an active layer reached 135.71 mW/cm2. Hence it can be concluded that the anode supported unit cell containing Ni-YMSZ anode can be used to develop high efficiency unit cells for high and intermediate temperature fuel cell applications. This process can also be applied to develop SOFC stack with multiple unit cells for high power output in future.
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