| 摘要: | 本論文之主旨為利用電化學交流阻抗頻譜法(Electrochemical impedance spectroscopy, EIS)，來解析(1) 氧化鑭鍶錳(Lanthanum Strontium Manganite, LSM)添加銀作為固態氧化物燃料電池(Solid oxide fuel cell, SOFC)陰極材料之電池性能特性，與(2) 質子交換膜燃料電池(Proton exchange membrane fuel cell, PEMFC)之膜電極組(Membrane Electrode Assembly, MEA)熱壓程序之對於反應介面影響。研究結果摘要如下：(1)氧化鑭鍶錳添加銀作為固態氧化物燃料電池陰極材料之研究結果：探討銀添加量對於電池性能影響之原因。由EIS分析發現Relectrolyte值與Roxy值因釔穩定氧化鋯（Yttria stabilized zirconia，YSZ）電解質材料特性與未有促進氧離子在三相區(Triple phase boundary, TPB)傳遞效應之緣故，故兩值均未有明顯之變化。另外，隨銀添加量增加，Relectron值隨之下降，原因為銀在電極中提供更多電子傳導路徑。另一方面，隨銀添加量增加，Rchem值亦隨之下降。經化學分析電子儀(ESCA)分析原因發現在高溫與極化環境，銀由未帶電之Ag轉換至帶2價電之AgO，每一個轉換會產生2個電子，來協助三相區之氧還原反應進行。除此之外，在較低操作溫度(如700 ℃)，由於銀蒸發問題減緩，可保留足夠之電子傳導路徑與電子濃度來參與三相區氧還原反應。故相較於未添加銀之電極，含銀電極在700 ℃仍可獲得較佳電池性能。總結實驗結果，發現40 wt.%銀添加量可獲得較佳電池性能。此外，探討燒結溫度改變對於電池性能影響之原因。由掃描式電子顯微鏡/能量散佈分析儀(SEM/EDS)觀察結果，發現隨燒結溫度增加會影響銀球基底擔載LSM電極顆粒之堆疊結構。另外，隨燒結溫度增加，則銀損失速率隨之增加，代表銀逸散量增加，使得電子傳導路徑減少。另外，由ESCA分析結果，發現隨燒結溫度增加，由Ag轉換至AgO過程生成之電子濃度亦減少，因此參與三相區氧還原反應之電子隨之遞減，影響電池整體性能變化。總結實驗結果，850 ℃為銀添加之LSM電極較佳之製備燒結溫度。(2)質子交換膜燃料電池之MEA熱壓程序對於反應介面影響之研究結果：由EIS與I-V極化曲線分析比對發現，Rif值可作為PEMFC電池性能評估之指標參數。首先分析改變熱壓壓力之影響，發現改變熱壓壓力並未影響電極中白金觸媒(固相)與Nafion膜或Nafion溶液(液相)之兩相介面區反應(亦即電極之觸媒活性幾乎一致)，僅影響電極中三相介面區反應。另外，分析改變熱壓溫度之結果，發現改變熱壓溫度，首先影響電極中之兩相介面區反應，但由於兩相介面區反應受到Nafion膜溫度效應之影響，故再間接影響到三相介面區之反應。The diagnosis technology of electrochemical impedance spectroscopy (EIS) was been used in the research for investigate the electrochemical kinetics in the system of (1) Ag powders were mixing with the LSM powders as cathode electrode material of solid oxide fuel cell (SOFC) and (2) the reaction interface effect of membrane electrode assembly (MEA) in proton exchange membrane fuel cell (PEMFC) by hot-pressing process. The results and contributions of the research were been summary as following:(1) The effect of different Ag mixing amount in the cathode electrode for cell performance was investigated by EIS. The values of Relectrolyte and Roxy were almost constant value, and they related to the electrolyte material properties of yttria stabilized zirconia (YSZ) and unenhanced the transfer property of oxygen ion in triple phase boundary (TPB) in cathode electrode. Moreover, the values of Relectron were decreased following the Ag content increasing, and it related that the Ag provided more electron conduct routes in the cathode electrode. On the other side, the values of Rchem were also decreased following the Ag content increasing, and it related that the Ag of electrically neutral was transformed to divalent of AgO on the electrode by ESCA analysis, and the transformation process produced more electrons to improving the oxygen reduction reaction (ORR) in TPB. In addition, the problem of Ag evaporation was been retard in the lower operation temperature (as 700 ℃). Therefore, electron conduct routes were retained in the cathode electrode and more electrons to improving the ORR in TPB at 700 ℃. Compared with Ag-containing and Ag-free cathode electrode that the Ag-containing cathode electrode could get better cell performance at 700℃. Finally, experiment results were summarized that the optimal Ag content was 40 wt.%.In addition, the effect of different electrode sintering temperature for cell performance was also investigated by EIS. However, the supporting structure of LSM particles supported on Ag-spheres was changed following the sintering temperature of electrode increasing by the analysis of scanning electron microscope (SEM) / energy dispersive spectrometer (EDS). On the other side, the Ag evaporation rate was also increased following the sintering temperature of electrode increasing. Therefore, the Ag evaporation mount was increased and caused electron conduct routes decreasing in the cathode electrode. In addition, the electron concentration was reduced by Ag transformed to AgO on the electrode. Therefore, the reaction of more electrons to improving the ORR in TPB was reduced, and affected the cell performance. Finally, experiment results were summarized that the optimal sintering temperature of Ag-containing cathode electrode was 850 ℃.(2) The value of Rif was an optimal index for the estimating of PEMFC performance by compared with EIS and I-V polarization curve. The MEA was prepared by hot-pressing process and used different hot-pressing pressure or temperature. The reaction interface effect of the MEA by hot-pressing pressure or temperature was investigated. When the hot-pressing pressure was changed, and the two phase interface reaction boundary of Pt catalyst/ Nafion membrane or Pt catalyst/ Nafion solution was not influenced. The varying of hot-pressing pressure just only influenced the triple phase interface reaction boundary. On the other side, when the hot-pressing temperature was changed, and it influenced two phase interface reaction boundary, firstly. Because two phase interface reaction boundary was influenced by temperature effect of Nafion membrane. Therefore, it indirect influenced for the reaction of triple phase interface boundary. |
