利用偶合劑提升直接甲醇燃料電池觸媒有效利用率之研究

Study of Using Silane Coupling Agents to Improve the Catalysts Utilization in Direct Methanol Fuel Cells

吳富其(Fu-Chi Wu)

指導教授 ： 萬其超 ； 王詠雲

國立清華大學/工學院/化學工程學系/博士(2006年)

摘要

由於具有高能量密度（4825.7 kWh/l）、可快速填充燃料、以及可簡化電池系統設計的優點，使得直接甲醇燃料電池近年來受到全世界廣大的注意，頗有機會在最近幾年內商業化，尤其是應用在消費性可攜式電子產品上。然而，在直接甲醇燃料電池商業化前有兩個必須克服的難題，那就是甲醇橫渡與觸媒有效利用率偏低。
為了瞭解影響觸媒有效被利用率的因素，我們先從電池之工作原理探討何謂有效的觸媒著手，再從觸媒漿料之基本分散原理分析觸媒漿料之分散現象，並且回顧相關文獻。從分析中發現，若直接利用漿料中的全氟磺酸化離子高分子，作為觸媒顆粒的保護基以形成立體障礙排斥作用，將可達到最佳的分散效果。然而，在正常情形下，全氟磺酸化離子高分子與觸媒顆粒無法形成有效的立體障礙排斥效應，原因是兩者化學特性上的差異甚大，使得彼此間的吸附性差，於是，需要增進兩者之吸附性以提升觸媒有效被利用率。
本研究重點在利用偶合劑來改質白金觸媒顆粒，使全氟磺酸化離子高分子可稼接在白金表面上鍵結，形成立體障礙排斥效應促進白金觸媒漿料之分散以提升觸媒的有效利用率。我們利用ESCA及NMR來驗證整個偶合反應、EQCM來探討偶合劑在白金表面之自組裝速率及阻礙效應、EXAFS來探討經偶合劑處理前後電極之白金顆粒的分散情形。我們並將電極組裝成MEA進行放電效能測試，再以CV分析經白金觸媒之有效被利用率。由實驗結果發現，使用偶合劑處理確實可提升觸媒之有效利用率，證實了該構想的可行性。

關鍵字

直接甲醇燃料電池 ； 觸媒有效率用率 ； 偶合劑

並列摘要

Direct methanol fuel cell (DMFC) is receiving great attention worldwide in recent years due to following features: high energy density of liquid methanol (~ 4825.7 kWh/l), quick re-fueling, and simple cell design. DMFC is among the most promising type of fuel cells to be commercialized in the near future, especially for use in 3C application. However, two major obstacles of DMFC need to be overcome. Naturally, methanol crossover and low catalyst utilization.
To understand the factors that affect catalyst utilization, we firstly investigated what an effective catalyst is from the operating mechanism of DMFC. Then, we analyzed the dispersion of catalyst paste, and reviewed past effects to seek the solution to improve catalyst utilization. We have hence developed a logical and simplest way to improve dispersion and subsequent catalyst utilization by using PFSI, which is one of the main components of catalyst paste, as the protecting agent instead of adding any other agent. However, it is difficult to form the steric stabilization between chemically dissimilar Pt nanoparticle and PFSI. The affinity between particle and PFSI needs to be enhanced.
In this study, we have created a bonding between particles and PFSI by using silane coupling agents to improve catalyst utilization. Firstly, we identified the coupling reactions by using ESCA and NMR, and then characterized the self-assembly rate, blocking effect, dispersion, MEA performance, and catalyst utilization before and after coupling agent treatment by using EXAFS and electrochemical methods. The results indeed proved the validity of our concept and the use of coupling agent can help improve the catalyst utilization.

並列關鍵字

Direct Methanol Fuel Cell ； Catalyst Utilization ； Silane Coupling Agent

參考文獻

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