臺灣博碩士論文加值系統

本研究的目的是利用電泳披覆(EPD)製程應用於質子交換膜燃料電池(PEMFC)的領域，使用奈米級Pt/C與乙二醇(EG)合成之Pt/CNT觸媒粉體，經電泳披覆製程製作電池膜極組(MEA)。選擇水系溶劑混合最佳比例之Pt/C觸媒及離子聚合物(Nafion Ionomer)，改變懸浮液酸鹼度值，探討對懸浮液之穩定性及分散性狀況；當pH值為8時，觸媒粉體表面Zeta電位值為-54.8 mV，粉體之分散性頗佳且懸浮穩定度亦良好。當溶劑中離子聚合物為23.2 wt%固含量時可獲得最佳的觸媒電化學活化面積(EAS)。比較並探討EPD製程與傳統熱壓製程製備的膜極組(MEA)之發電效能優劣，從測試數據中發現EPD製程製備之膜極組，其電池效能(154 mW/cm2)較傳統熱壓製程(122.3 mW/cm2)佳，從SEM顯微結構發現熱壓後的觸媒團簇更趨嚴重，使得反應三相點呈減縮，且交流阻抗分析結果指出熱壓後電極阻抗變大。EPD製備之0.2 mg/cm2 Pt膜極阻其電池效能(154 mW/cm2)優於商用E-TEK 0.4 mg/cm2 Pt厚層疏水電極(122.1 mW/cm2)。水分的濃度與前驅物(H2PtCl6•6H2O)添加速度對Pt奈米觸媒粒徑之影響。當反應溶劑中去離子水的含量從0-30 vol%將造成Pt奈米觸媒粒徑分佈由2.4-4.2 nm。此乃水分多寡影響反應溶劑之pH值，並促成粒徑尺寸與分散狀態之差異。吾人以合成之18.6 wt% Pt/CNT觸媒粉體與商用E-TEK 20 wt% Pt/C觸媒粉體作一電池效能比較，從SEM顯微圖像發現觸媒電極其孔隙率較Pt/C觸媒粉體電極來得高，使得Pt觸媒使用率獲得提升，如此使得電極反應三相點增加，故電池效能亦隨之提升。

In this study, the multi-walled carbon nanotubes (MWNTs) were treated through a chemical oxidation by mixture of nitric acid and sulfuric acid. Nearly monodispersed nanosized platinum catalysts (2-3 nm) for proton exchange membrane fuel cells (PEMFCs) were synthesized by the reduction of hexachloroplatinic (IV) acid precursor with ethylene glycol (EG) solvent at 50oC, which were simultaneously distributed over the surface of the carriers of MWNTs. The structure and materials of membrane electrode assembly (MEA), which was in form of nanoscaled Pt/C and Pt/CNT catalysts coated by electrophoretic deposition (EPD) onto Nafion membrane to be sandwiched with the carbon-based electrodes of PEMFC such as carbon fabric, become the key component to booster the entire power efficiency of PEMFC. The goal of this study is to develop the novel processing technique to enhance the efficiency of catalyst loading and distribution on the electrodes, because of considerable cost for novel metal catalysts materials such as Pt.
Prior to the EPD process, the choice of aqueous solution of adequate acidity with optimized ratio of Pt/C nanocatalysts and Nafion ionomer to prepare the EPD suspension with a good colloidal stability and dispersivity. The zeta potential of Pt/C particles in the suspension is -54.8 mV for pH value was tuned approximately at 8 to maintain good suspension stability. The electrochemical active area (EAS) of nanocatalysts reached the highest value as solid content of Nafion ionomer in the suspension was 23.2%.
The results show that the performance of fuel cell with the MEA prepared by EPD technique was (154 mW/cm2) excels that of MEA prepared by the conventional hot press method (122.3 mW/cm2) because the nanocatalysts were heavily agglomerated by the hot press process, which led to a significant reduction of available triple-phase areas in the electrodes from SEM observation and an increase of impedance of electrodes by AC impedance measurement. The EPD process proved to have lower Pt loading for MEA fabrication (0.2 mg Pt/cm2) and better cell performance as compared the commercial E-TEK MEA (0.4 mg Pt /cm2) with hydrophobic treatment. The size of nanosized platinum catalysts (2.4-4.2 nm) by the reduction of H2PtCl6.6H2O precursor and EG solvent is affected by water content (0-30 vol%) in the solution and the influx rate of Pt precursor. The water content is in conjunction with the variation of pH value of reaction solution and the dispersion of synthesized Pt particles. It is also noticeable that the PEM fuel cells with Pt/MWNT nanocatalysts (18.6 wt%) had an increased power performance than the commercially available Pt/C nanocatalysts (20 wt%, Pt on Vulcan XC-72, E-TEK) for the catalyst effectiveness for Pt/MWNT is much higher with an increase of porosity and triple-phase areas in the electrode.

中文摘要 I

英文摘要 II

目錄 IV

圖目錄 VII

表目錄 XI

第一章 緒 論 1

1.1 燃料電池簡介 1

1.2 質子交換膜燃料電池的發展 6

1.3 燃料電池之電極材料 7

1.4 電泳技術發展簡介 8

1.5 電泳懸浮液系統種類 10

1.6 研究目的及重點 14

第二章 理論基礎 15

2.1 電泳披覆機制 15

2.2 電泳粒子表面電荷來源 16

2.3 表面電位之基本概念 19

2.4 電雙層理論 20

2.5 工作電場所影響的電雙層結構 23

2.6 膠體化學與DLVO理論簡述 24

2.7 高分子的空間穩定作用 31

2.7.1 理論解釋兩種穩定機構 34

2.7.2 穩定機構的判斷 35

2.7.3 空間穩定效應的特點 36

2.8 懸浮液中粉體的沉降速率 37

2.9 定電壓與定電流之電泳披覆 38

第三章 實驗步驟與方法 41

3.1 EPD溶劑的選擇 41

3.2 以循環伏安法決定離子聚合物添加最適化 42

3.3 電泳批覆法製備膜極組 44

3.4 觸媒鍍層組成量測 45

3.5 多壁奈米碳管載體之鉑觸媒製備流程 50

3.6 發電效率測試 52

3.6.1 五層膜極組單電池組裝 52

3.6.2 燃料電池測試條件 54

第四章 結果與討論 57

4.1 EPD懸浮液之製備與最適化 57

4.1.1 EPD懸浮液溶劑之選用 57

4.1.2 Zeta電位量測與DLS粒徑分析觸媒粉體於三種溶劑之
差異 59

4.1.3 觸媒粉體表面帶電荷最佳化 64

4.1.4 藉由循環伏安曲線分析觸媒於三種溶劑中之分散行為 65

4.2 EPD製程參數的測試與評估 66

4.2.1 找尋電泳披覆參數最佳化 66

4.2.2 Nafion離子聚合物含量對電泳披覆的影響 69

4.3 Nafion離子聚合物含量對觸媒粉體之電化學活化反應的
影響 71

4.4 EPD製程製備之膜極組與傳統熱壓法之發電效能比較 75

4.5 EPD製程製備之膜極組與商用E-TEK膜極組的效能比較 79

4.6 利用多璧奈米碳管作為Pt催化劑載體合成Pt觸媒粉體 82

4.7 奈米Pt金屬觸媒材料分析 86

4.8 商用E-TEK Pt/C及Pt/MWNT膜極組之單電池效能分析 91

4.9 未來研究方向 96

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