Pt/nCNT觸媒於質子交換膜燃料電池與質子交換膜水電解器之應用研究

本研究探討利用微波輔助加熱還原法沉積Pt觸媒於含氮奈米碳管(nCNT)應用於質子交換膜燃料電池與水電解器，nCNT使用化學氣相沉積法合成，藉由改變生成觸媒與氮碳源比例、氮碳源供給速率、載流氣體以及反應溫度，合成不同管徑與氮摻雜比例之奈米碳管。Pt是目前氧還原反應(ORR)最佳的觸媒，但Pt存量稀少且價格昂貴，而氮摻雜奈米碳管有加強ORR活性和增進穩定性的效用，希望藉此提升ORR活性以減少Pt的使用量，並延長使用壽命。使用化學氣相沉積生成7種nCNT樣本，並利用微波輔助加熱還原法合成為7種不同的Pt/nCNT觸媒，從HRTEM觀察管徑與結構以及Pt觸媒粒子的大小、形狀和分布情形；nCNT含氮量的多寡以元素分析(EA)測定；Pt沉積於nCNT表面總量藉由ICP取得；XPS分析表面官能基鍵結組成；TGA推估觸媒樣本的抗氧化力；Raman光譜評估碳載體nCNT的石墨化；循環伏安法量測電化學活性表面積並評估衰退率。將觸媒製作成MEA，分別在質子交換膜燃料電池和質子交換膜水電解效能測試。研究結果顯示，nCNT平均管徑分佈自19.6 nm至48.4 nm，標準偏差在9.2 nm和23.4 nm之間，生成溫度對管徑的影響最顯著，其次是觸媒含量，根據生成條件的不同，氮摻雜總量在0.9 wt. % ~ 6.8 wt. %；Pt粒子沉積量在17.0 wt. % ~ 22.2 wt. %之間，根據載體基材種類結構性質的不同，平均粒徑在2.87 ~ 4.75 nm之間；XPS結果顯示較高的氮含量可以使Pt粒子以高比例的Pt0存在於表面；TGA結果可見氮的摻雜可有效提高nCNT的抗氧化能力，Pt/nCNT最大質量損失溫度可達523 ℃，比Pt/pCNT的474 ℃高58 ℃，碳材的石墨化程度ID/IG在0.76 ~ 0.90之間，所提高的熱穩定性和電化學穩定性，與氮摻雜的效果相比較不明顯；Pt/nCNT的活性(20.88 m2/g)略低於商購Pt/C(E-TEK)(21.72 m2/g)，Pt/nCNT經過600 cycles循環操作，衰退率與Pt/C(E-TEK)相比較低，穩定性較佳；燃料電池效能測試中，電荷轉移電阻為影響燃料電池效能的主要原因，Pt/nCNT在0.6 V的電流密度可達513.2 mA/cm2；考慮水電解實際應用的工作電壓，Pt/nCNT於2.0 V的電流密度為50 mA/cm2，產氫速率1.93 ml/min，需要80 ℃溫度達到最大效能，不使用GDL時，仍能保持相同的效能。

關鍵字

Pt-based觸媒；含氮奈米碳管；特性分析；質子交換膜燃料電池；質子交換膜水電解

並列摘要

This study investigated the use of microwave-assidted heating method to deposit Pt catalyst on nitrogen-containing carbon nanotubes(nCNT) for proton exchange membrane fuel cell(PEMFC) and proton exchange membrane water electrolysis(PEMWE). nCNT with different nitrogen contents were obtained with different ratios of precursor source, precursor supply rates, carrier gas and reaction temperature applied in chemical vapor deposition(CVD) technique. Pt is the best catalyst for oxygen reduction reaction(ORR), but Pt is noble metal. nCNT and enhance ORR activity and stability characteristics. can reduce Pt usage and extend catalyst life. Look forward to using nCNT as supports that can enhance the Pt utilization ratio, activity and stability. In this study, nCNT sample was prepared by chemical vapor deposition. Using microwave-assidted heating method to deposit Pt on nCNT. The microstructure and morphology of the catalysts were characterized by transmission electron microscopy(TEM). The Pt content and elemental content of the catalysts was tested by inductively coupled plasma (ICP) and Elemental analysis(EA). X-ray photoelectron spectroscopy (XPS) was employed to characterize surface function groups. Thermogravimetric analysis(TGA) and Raman spectroscopy was employed to analyze oxidation resistance and nCNT graphitization. Cyclic voltammetry was employed to determine electrochemical surface area and degradation. Evaluating the catalyst of the fuel cell and water electrolysis performance. The results showed that the nCNT mean diameter was about 19.6 ~ 48.4 nm between the standard deviation of about 9.2 ~ 23.4 nm, with reation temperature increase. Pt content and nCNT nitrogen content were 17.0 wt. % ~ 22.2 wt.% and 0.9 wt. % ~ 6.8 wt. %, respectively. The mean Pt particles was about 2.87 ~ 4.75 nm. XPS exhibited higher nitrogen content nCNT that Pt0 function of Pt particles was higher. TGA showed N-doped CNT has higher oxidation resistance. Pt/nCNT maximum mass loss temperature(532 ℃) higher than Pt/pCNT(474 ℃) 58 ℃. nCNT graphitization ID/IG were between 0.76 ~ 0.90. Pt/nCNT sample that Electrochemical surface area(20.88 m2/g) slightly lower than Pt/C(E-TEK)(21.72 m2/g), but Pt/nCNT had better stability than Pt/C(ETEK). A PEMFC performance with Pt/nCNT gave current densities of 513.2 mA/cm2 at 0.6 V. A PEMWE performance with Pt/nCNT gave current densities of 50 mA/cm2 and H2 rate of 1.92 ml/min at 2.0 V. In PEMWE, Pt/nCNT had maximum efficiency at 80 ℃ and it maintained the same performance without GDL.

並列關鍵字

proton exchange membrane water electrolysis ； Pt-based catalyst ； nitrogen-containing carbon nanotubes ； characterization analysis ； proton exchange membrane fuel cell

參考文獻

Antolini, E. "Carbon supports for low-temperature fuel cell catalysts" Applied Catalysis B: Environmental, 88, 24, 2009

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Burch, H. J., Davies, J. A., Brown, E., Hao, L., Contera, S. A., Grobert, N. and Ryan, J. F., "Electrical conductance and breakdown in individual CNx multiwalled nanotubes" Applied Physics Letters, 89, 143110, 2006

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國際替代計量

Pt/nCNT觸媒於質子交換膜燃料電池與質子交換膜水電解器之應用研究

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