以無機分散劑製備質子交換膜燃料電池(PEMFC)陽極

本研究主要宗旨為利用較為簡易的製程且對環境較為友善的無機分散劑(蒙脫土)製備質子交換膜燃料電池單電池，並與傳統有機製備方式做比較。首先以超音波震盪法分散碳黑，利用無機分散劑改善其親水度，藉以增加碳黑對白金(Pt)接觸面積，以期達到減少白金用量的目的；第二步，利用化學熱回法將氯鉑金(H2PtCl6)在乙醇溶液中加熱至80oC生成氫氣(H2)、氯氣(Cl2)與白金，氫氣與氯氣經10oC的冷凝管離開系統，留下的白金與分散劑在高溫與攪拌下會與碳黑結合，形成Pt/C觸媒；第三步，將製備完成的Pt/C觸媒以刮刀塗佈於聚四氟乙烯(PTFE)薄膜上，再以125oC、120psi條件下將觸媒熱轉印至Nafion 212薄膜兩側，後撕除聚四氯乙烯薄膜，並組合成單電池樣品。本實驗利用無機分散劑與有機分散劑(春大地 AS-1164)以不同分散頻率(40kHz、80kHz、120kHz)再披覆10%wt與20%wt的白金，做排列組合製備出10種不同的單電池樣品，並與市售單電池做比對。在常溫下以20sccm的氫氣流量進行發電測試，市售單電池發電功率密度為4.24mW/cm2。在經120 kHz震盪3小時，白金含量為10%wt的條件下，有機分散劑樣品的表現為 3.694mW/cm2，無機分散劑樣品的表現為4.49 mW/cm2；有機分散劑樣品相較市售單電池低12.9%，無機分散劑樣品相較市售單電池有5.89%的發電效率提升。以相同震盪頻率製備樣品並提升白金含量其發電效率可以再提升。此外無機分散劑經震盪3小時並披覆10%wt含量的白金條件下，120kHz與40kHz發電效率分別為4.49mW/cm2與0.95 mW/cm2，可見高頻分散有助於白金的平均分布。目前主流製程仍以有機分散劑為主，但其對環境不友善(如：揮發後會形成有毒氣體、直接排放會造成汙染……等)，研究結果得知發電效率不如無機分散劑。無機分散劑樣品透過掃描式電子顯微鏡(SEM)觀察可發現其具有鋁氧八面體的結構，比有機分散劑在相同比例下使碳黑有更強的白金吸附能力，並於金相顯微鏡下觀察其表面白金也分散較為均勻，能有較大的化學反應面積，以及使用四點探針量測可發現其有較佳的電阻率與使用水接觸角系統檢測陽極觸媒層時有較佳的親水性。

關鍵字

無機分散劑；聚四氟乙烯(PTFE)薄膜；熱回流法；質子交換膜燃料電池(PEMFC)

並列摘要

The main purpose of this research is to study a single proton exchange membrane fuel cell by using a simple process and an environmentally friendly inorganic dispersant, and to compare with traditional methods by using organic dispersant. First, the hydrophilicity of carbon black was improved by using an inorganic dispersant and ultrasonic stirring, and the contact area of carbon black to platinum is increased. Second, hydrogen (H2), chlorine (Cl2) and platinum were prepareed by Chloroplatinic Acid (H2PtCl6) heating to 80oC in ethanol solution with chemical thermal recovery method. The Pt/C catalyst is prepared by mixing remaining platinum and dispersant with carbon black under high temperature. Third, the prepared Pt/C catalyst was coated on a polytetrafluoroethylene film by a doctor blade. The membrane electrode assembly was made by thermally peering the polytetrachloride off both sides of the Nafion 212 film at 125 oC and 120 psi. Finally, the single fuel cell sample is completed by coupled the membrane electrode assembly, two gas diffusion layers, and two bipolar plates. In this experiment, 10 different combinations of single fuel cells were selected by coating 10%wt and 20%wt of platinum catalyst with inorganic and organic dispersants, and three frequencies (40kHz, 80kHz, 120kHz). Performance comparisons were made with commercial available single cells at a constant temperature of 20 sccm hydrogen flow rate as the base line. The power density of commercially available single fuel cell is 4.24 mW/cm2. With 10%wt of platinum coating and 120 kHz for 3 hours stirring, the organic dispersant sample showed 3.694 mW/cm2, and the inorganic showed 4.49 mW/cm2. The inorganic dispersant sample has 5.89% higher and the organic dispersant sample is 12.9% lower. This research showed that the single fuel cell can be improved by using an environmentally friendly inorganic dispersant.