合成具甲醇電催化活性及穩定性之鉑/離子液體/奈米碳管

Abstract

本研究利用乙二醇作為還原劑在離子液體的輔助下，將六氯鉑酸根離子還原於奈米碳管上，形成鉑/離子液體/奈米碳管複合材料。選用四種不同陰離子(六氟磷酸根、氯離子、溴離子以及碘離子)之1-丁基-3-甲基咪唑系列離子液體製備奈米複合材料，並將其用於直接甲醇燃料電池的陽極進行甲醇氧化反應之催化。發現離子液體陰離子對於在奈米碳管上形成小尺寸鉑奈米粒子扮演重要的角色，但只有[BMIM][PF6]和[BMIM][Cl]對於製備鉑/離子液體/奈米碳管複合材料擁有再現性，形成鉑奈米粒子平均粒徑分別為2.8 ± 0.3及2.6 ± 0.2 nm。在電化學的測試中，所製備的Pt/[BMIM][PF6]/CNT、Pt/[BMIM][Cl]/CNT、Pt/CNT奈米複合材料以及商用鉑粉修飾電極之電化學活性表面積分別為62.8、101.5、78.3及87.4 m2 g-1；另外，Pt/[BMIM][Cl]/CNT奈米複合材料提供比商用鉑粉更高的質量活性（251.0 A g-1）以及較低的開路電位（-0.60 V），而甲醇氧化電流（If）與一氧化碳毒化氧化電流密度（Ib）比值最高（4.52）表示電極不易受一氧化碳吸附所毒化。經過20000秒掃描後，Pt/[BMIM][Cl]/CNT奈米複合材料修飾電極仍具有很好的穩定性。Pt/[BMIM][Cl]/CNT奈米複合材料具有高電化學活性、穩定性以及成本效益等優勢，故具有作為直接甲醇燃料電池的陽極催化劑之潛力。

Platinum (Pt) nanoparticles (NPs) on carbon nanotubes (CNTs) supports from PtCl62– ions through a facile ionic liquid (IL)-assisted method using ethylene glycol as a reducing agent has been developed and used for methanol oxidation. 1-Butyl-3-methylimidazolium (BMIM) with four different counter ions (PF6-, Cl-, Br-, and I-) have been tested for the preparation of Pt/IL/CNT nanohybrids, showing the counter ions of the ILs play an important role in the formation of small sizes of Pt NPs on the CNT supports. Only [BMIM][PF6] and [BMIM][Cl] allow reproducible preparation of Pt/IL/CNT nanohybrids, with average diameters of 2.8 ± 0.3 and 2.6 ± 0.2 nm for Pt NPs, respectively. The IL molecules adsorbed on the surfaces of CNTs interact with PtCl62– ions prior to their reduction and then stabilize the as-formed Pt NPs, leading to the formation of monodispersed and stable Pt NPs. The electroactive surface areas of as-prepared Pt/[BMIM][PF6]/CNT, Pt/[BMIM][Cl]/CNT, Pt/CNT nanohybrids, and commercial Pt/C NPs electrodes are 62.8, 101.5, 78.3, and 87.4 m2 g-1, respectively. The Pt/[BMIM][Cl]/CNT nanohybrid-modified electrodes provide higher catalytic activity (251.0 A g–1) toward methanol oxidation at a negative onset potential of -0.60 V (vs. Ag/AgCl) than commercial Pt/C-modified ones do (133.5 A g–1) at -0.46 V. Among the tested electrodes, the Pt/[BMIM][Cl]/CNT electrode provides the highest ratio (4.52) of forward/reverse oxidation current peak, revealing an efficient oxidation of methanol and a little accumulation of carbonaceous residues at the catalyst surface. The Pt/[BMIM][Cl]/CNT electrode is stable after sweeping at least for 20,000 s. With advantages of high electrochemical activity, stability, and cost effectiveness, the Pt/[BMIM][Cl]/CNT nanohybrids hold great potential as an efficient anode catalyst for direct methanol fuel cells.