Probing lithium and alumina impurities in air- and water stable ionic liquids by cyclic voltammetry and in situ scanning tunneling microscopy
Probing lithium and alumina impurities in air- and water stable ionic liquids by cyclic voltammetry and in situ scanning tunneling microscopy
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DOI：
10.1524/zpch.2006.220.10.1377
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发表时间：
2006-01-01
影响因子：
2.5
通讯作者：
Borissenko, Natalia
中科院分区：
文献类型：
--
作者：
Endres, Frank;El Abedin, Sherif Zein;Borissenko, Natalia
本文报道了离子液体在电化学窗口阴极极限的电化学击穿和离子液体中无机杂质（源于合成前）在电极/电解质界面上的原位扫描隧道显微镜在An（111）上的探测的一些结果。结果表明，Au（111）在超纯1-丁基-1-甲基吡咯烷双（三氟甲基磺酰基）酰胺（[Py-1.4] Tf_2N）中的重构/再构导致了蠕虫状表面结构向具有良好台阶结构的表面的转变。接近液体的阴极分解，STM图像的质量变得更差，并且在大量离子液体分解的开始时，在金表面上形成膜，最终完全屏蔽金阶地。当[Py-1.4]Cl和LiTf_2N通过复分解反应制得的[Py-1.4] Tf_2N液体在合成后未被彻底洗涤时，原位STM照片显示在宽电位范围内与超纯液体相同的表面结构，但在阴极区仅观察到少量单层锂的沉积。在Au（111）上的循环伏安图中有明显的锂沉积的证据，我们进一步证明了光谱上超纯的1-乙基-3-甲基咪唑双（三氟甲基磺酰基）酰胺离子液体（[EMIm] Tf 2N）在合成后进行Al 2 O3处理以除去有机杂质时，在电极/电解质界面上显示出意想不到的行为。Al 2 O3以低浓度溶解在离子液体中并沉积在电极表面。在较低的电极电位下，氧化铝似乎被还原成金属铝。我们的研究结果表明，即使是超纯的离子液体可以包含无机杂质，这是非常难以探测与传统的分析方法。更好的合成路线将是必要的，使超纯离子液体的基础物理化学研究。
In this paper we report on some results on the electrochemical breakdown of ionic liquids at the cathodic limit of the electrochemical window and on the probing of inorganic impurities in ionic liquids (originating front the synthesis) at the interface electrode/electrolyte by in situ scanning tunneling microscopy on An(111). It will be shown that the restructing/reconstuction of Au(111) in ultrapure 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py-1.4]Tf2N) lead to a transition from a wormlike surface structure to a surface with well defined terraces. Close to the cathodic decomposition of the liquid the quality of the STM pictures gets worse and at the onset of massive ionic liquid breakdown a film forms on the gold surface finally shielding completely the gold terraces. When the [Py-1.4]Tf2N liquid, made by a metathesis reaction from [Py-1.4]Cl and LiTf2N, is not thoroughly washed after the synthesis, the in situ STM pictures show in I wide potential range the same Surface Structures as with the ultrapure liquid, but in the cathodic regime the deposition of lithium in only a few monolayers is observed. In the respective cyclic voltammograms on Au(111) there is clear evidence for lithium deposition.We show furthermore that a spectroscopically ultrapure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquid ([EMIm]Tf2N) call show unexpected behaviour at the electrode/electrolytc interface when after synthesis it is subject to an Al2O3 treatment with the aim to remove organic impurities. Al2O3 seems to be dissolved in the ionic liquid in low concentrations and deposited at the electrode Surface. At lower electrode potentials the alumina seems to be reduced to metallic aluminium. Our results show that even ultrapure ionic liquids can contain inorganic impurities which are very difficult to probe with conventional analytical methods. Better synthesis routes will be necessary to make ultrapure ionic liquids for fundamental physicochemical studies.