反微胞法製備Pt/MWNT觸媒應用於質子交換膜燃料電池之研究

Study on Pt/MWNT Electrocatalysts Prepared by Reverse Micelle for Proton Exchange Membrane Fuel Cells

邱昭瑞(Jhao-Ruei Ciou)

指導教授 ： 江右君

元智大學/工程學院/機械工程學系/碩士(2011年)

摘要

質子交換膜燃料電池(PEMFCs)最主要的關鍵技術之一即為電化學觸媒；目前已知Pt為PEMFCs活性最佳的觸媒，在氧化還原能力上優於其他金屬。一般而言，有兩種方式可以增加觸媒活性，其一為減小Pt 奈米粒子之粒徑，另一方法為改善觸媒披覆在基材上之分散性，皆期望提高與燃料之反應面積，增加化學反應速率。
本研究利用反微胞法，利用檸檬酸與硫酸/硝酸混酸氧化多壁奈米碳管(Multi-walled carbon nanotubes, MWNTs)與自行合成氮奈米碳管，接著在氧化碳管的表面沈積奈米Pt粒子(20 wt. %)，考慮合成溫度的影響。使用材料檢測技術進行特性分析，並利用循環伏安法分析樣本的電化學特性。最後評估觸媒的燃料電池效能，並與商用Pt/C (E-TEK, 20 wt. %)觸媒比較。期能藉由MWNT作為載體，有效提升觸媒的利用率、活性和穩定性。
研究結果發現觸媒表面合成出均勻分散之奈米Pt 粒子，顆粒大小< 10nm。平均Pt 顆粒約在3.1~ 4.8 nm 之間，標準偏差約1.2 nm~2.2 nm，隨著合成溫度的增加而變大。經XRD分析其結晶性均優於商用Pt/C (E-TEK, 20 wt. %)，同時Pt 粒子可均勻分散在碳管表面。Pt/MWNT 樣本表面的O/C 比值隨合成溫度的提高而稍降，表示在惰性環境下熱處理會釋出表面氧原子，也間接導致Pt 還原態比例的增加。Pt/MWNT觸媒樣本之半電池ESA (Electrochemical surface area)均介於37-47 m2/g，樣本合成溫度較高者，衰退比率較低，Pt之利用率皆在67 %以上。燃料電池極化曲線測試結果顯示，各觸媒樣本於0.6 V之電流密度介於121~638 mA/cm2，最大功率密度介於100~815 mW/cm2。

關鍵字

燃料電池 ； 奈米碳管 ； 反微胞法 ； 觸媒 ； Pt ； 熱處理 ； 特性分析

並列摘要

Electrochemical catalyst that is the important key technologies for Proton exchange membrane fuel cells (PEMFCs); Currently, Pt metal is the best activity for the PEMFCs, the redox ability than other metals. In general, there are two ways to increase the catalytic activity, one for the reduced Pt nanoparticles size, another way to improve the catalyst coated on the substrate of the dispersion, are expected to improve with fuel reaction area and increased chemical reaction rate.
In this study, using reverse micelle method to deposit Pt nanoparticles (20 wt. %)on the citric acid and sulfuric acid/nitric acid oxidized multi-walled carbon nanotubes (MWNTs), and with nitrogen-doped carbon nanotubes, consider the effect of synthesis temperature.Several material analytical techniques were utilized to characterize the properties and using cyclic voltammetry to analyze electrochemical properties. Final, evaluating the catalyst of the fuel cell performance, and compared with the commercial Pt / C (E-TEK, 20 wt.%) Catalyst. Look forward to using MWNT as supports that can enhance the utilization ratio, activity and stability.
The results showed that the surface of catalyst to synthesize the dispersed Pt nanoparticles, particles size <10nm. The mean Pt particles was about 3.1 ~ 4.8 nm between the standard deviation of about 1.2 nm ~ 2.2 nm, with the synthesis temperature increased larger. With XRD analyzed the Pt/MWNT samples crystallinity that was superior to commercial Pt/C(E-TEK, 20 wt.%), Pt nanoparticles can be dispersed in the carbon nanotubes surface. Pt / MWNT samples O/C ratio increased with the synthesis temperature in the surface and slightly decreased, In an inert environment, the surface heat treatment can be release oxygen atoms, but also lead to Pt ratio increase in reduction state indirectly. Pt/MWNT samples that ESA (Electrochemical surface area) were between 37-47 m2 /g for half cell, when the samples synthesis temperature higher and the decline rate was lower, The Pt was utilized more than 67 %. Fuel cell polarization curves showed that the catalyst samples at 0.6 V the current density were between 121 ~ 638 mA/cm2, the maximum power density were between 100 ~ 815 mW/cm2.

並列關鍵字

Reverse micelle ； Catalyst ； Pt ； Heat treatment ； Characterization analysis ； Fuel cell ； Carbon Nanotubes

參考文獻

張澔洧、張文翔、游竣翔和劉鎮維，“奈米級鉑材料的合成及應用”，Chemistry (The Chinese Chemical society, Taipei), 65(1), 27-33, 2007.

Bi, W., and Fuller, T. F., “Temperature effects on PEM fuel cell Pt/C catalyst degradation”, 1 PART 2 ed., pp 1235-1246, 2007.

Chen, Y., Wang, J., Liu, H., Li, R., Sun, X., Ye, S., and Knights, S., “Enhanced stability of Pt electrocatalysts by nitrogen doping in CNTs for PEM fuel cells”, Electrochemistry Communications 11, 2071-2076, 2009.

Chung, C. G., Kim, L., Sung, Y. W., Lee, J., and Chung, J. S. “Degradation mechanism of electrocatalyst during long-term operation of PEMFC”, International Journal of Hydrogen Energy 34, 8974-8981, 2009.

Cindrella, L., Kannan, A. M., Lin, J. F., Saminathan, K., Ho, Y., Lin, C. W., and Wertz, J., “Gas diffusion layer for proton exchange membrane fuel cells-A review”, Journal of Power Sources 194, 146-160, 2009.