直接甲醇燃料電池之陽極交流阻抗分析及應用奈米碳管為載體之鉑釕合金觸媒研究

The Studies of Anode Impedance and CNT-supported Pt-Ru Catalyst for Direct Methanol Fuel Cells

許寧逸(Ning-Yih Hsu)

指導教授 ： 顏溪成

國立臺灣大學/工學院/化學工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.01817

摘要

摘要

本研究應用電化學交流阻抗分析技術，探討直接甲醇燃料電池陽極部分的界面效應以及觸媒反應動力模式。並結合固定相角元件(CPEs)提出ㄧ創新的交流阻抗等效電路模型，其比傳統理想電容模型多考慮到界面效應及多孔性結構的因素，有效的模擬出與實驗相吻合的結果。此外，隨著操作電位的改變，甲醇氧化反應的動力模式亦可用此創新的等效電路模型加以模擬並得到合理的解釋。
本研究應用改良過的醇類化學還原法成功合成出奈米碳管為載體之鉑釕合金陽極觸媒(Pt-Ru/CNT)。其中Pt重量百分比占20%，Ru占10%，Pt/Ru原子數比約為1:1。使用自製Pt-Ru/CNT觸媒之直接甲醇燃料電池單電池的放電性能比商業化E-TEK觸媒高。其中陽極觸媒用量為4mgPtRu/cm2，將自製觸媒配成漿料塗佈於疏水性碳布上；陰極觸媒用量為4mg Pt-Black/cm2，是使用商業化E-TEK氣體擴散電極(GDE)。陰陽極電極在與杜邦質子交換膜Nafion 117熱壓，進料為1M MeOH，操作於40℃時可得到比商業化觸媒更佳的電池放電性能。由於其他實驗條件均固定，因此較佳的電池性能歸功於CNT的高導電特性，CNT造成均勻良好的觸媒界面型態以及還原於CNT上適當的Pt/Ru觸媒合金比例。
有鑒於一系列研究證實CNT有助於直接甲醇燃料電池放電性能。進一步改良合成高金屬含量配比的自製CNT為載體之觸媒(40wt%Pt-20wt%Ru/CNT)。研發創新的真空過濾法可將自製觸媒更均勻分散於疏水性碳布上，雖然觸媒比例提高但用量不變，陽極觸媒用量保持4mgPtRu/cm2，單電池測試結果，於80℃下功率密度大於100 mW/cm2。這可歸功於高金屬含量配比觸媒形成較薄的觸媒層，比較緊緻的觸媒層結構。以電化學交流阻抗技術模擬分析結果顯示，高金屬含量配比自製CNT觸媒有較低的界面阻抗。基於實驗與模擬的結果均顯示，自製CNT高金屬含量配比觸媒，非常適合作為直接甲醇燃料電池陽極觸媒。

關鍵字

直接甲醇燃料電池陽極 ； 奈米碳管 ； 陽極觸媒 ； 交流阻抗 ； 動態氫電極 ； 固定相角元件

並列摘要

Abstract

In this work, electrochemical impedance was used to analyze the reaction kinetics and interfacial characteristics of an anode in a direct methanol fuel cell (DMFC). An advanced equivalent-circuit model is proposed. The new model incorporates constant phase elements (CPEs) rather than conventional capacitors in the equivalent-circuits taking into account the porous structure of the anode, particularly that in the catalyst layer and at the anode/membrane interface. It effectively simulated the electrochemical characteristics of a DMFC porous anode. The impedance model incorporates the interface factor, resulting in excellent matches between the simulation results and the experimental data in the Nyquist and the Bode plots over a wide range of frequencies. In addition, the differences among methanol electrooxidation reaction kinetics at various operating potentials are clearly observed and satisfactorily explained using electrochemical impedance spectroscopy and the CPE-based equivalent-circuit model.
The performance of a single-cell direct methanol fuel cell (DMFC) using carbon nanotube-supported Pt-Ru (Pt-Ru/CNT) as an anode catalyst has been investigated. In this study, the Pt-Ru/CNT electrocatalyst was successfully synthesized using a modified polyol approach with a controlled composition very close to 20wt%Pt-10wt%Ru, and the anode was prepared by coating Pt-Ru/CNT electrocatalyst on a wet-proof carbon cloth substrate with a metal loading of about 4 mg cm-2. A commercial gas diffusion electrode (GDE) with a platinum black loading of 4 mg cm-2 obtained from E-TEK was employed as the cathode. The membrane electrode assembly (MEA) was fabricated using Nafion

並列關鍵字

Direct methanol fuel cell ； CNT ； Carbon nanotube ； electrochemical impedance spectroscopy ； dynamic hydrogen electrode ； constant phase element

參考文獻

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