Voltammetry of ferrocene in supercritical CO2 containing water and tetrahexylammonium hexafluorophosphate
Voltammetry of ferrocene in supercritical CO2 containing water and tetrahexylammonium hexafluorophosphate
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二茂铁在含水和六氟磷酸四己基铵的超临界CO2中的伏安法
DOI：
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发表时间：
1989
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通讯作者：
R. Wightman
中科院分区：
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作者：
D. Niehaus;M. E. Philips;A. Michael;R. Wightman
用微盘电极研究了二茂铁在含少量水的超临界CO2中的伏安氧化。在这些条件下获得的伏安图表明二茂铁的扩散速率很高，但显示出相当大的欧姆下降。通过向电池中添加四己基六氟磷酸铵((THA)PF{SUB 6})来减少伏安图的欧姆失真。然而，当向电池中加入大量(THA)PF{sub6}时，目视检查表明在所使用的条件下为两相系统。近红外光谱表明，上相为超临界CO{sub2}，下相为液体(THA)PF{sub6}。这一结果是在常压下纯(THA)PF{sub6}的熔点低于{℃}的温度下获得的。二茂铁在熔盐中的扩散系数要小得多。然而，记录在熔盐中的极限电流相对于上相并不衰减，因为二茂铁优先溶解在熔盐中。结果表明，当熔融盐少量加入电池时，起到了电极-表面改性剂的作用，提高了离子导电性，并允许从超临界CO2中提取的二茂铁被氧化。即使当电极处于较高的CO{sub2}相时，也会发生这种情况。
The voltammetric oxidation of ferrocene has been examined with microdisk electrodes in supercritical CO{sub 2} containing small-amounts of added water. Voltammograms obtained under these conditions indicate a high rate of diffusion for ferrocene but exhibit considerable ohmic drop. The ohmic distortion of the voltammograms is reduced by the addition of tetrahexylammonium hexafluorophosphate ((THA)PF{sub 6}) to the cell. However, when large amounts of (THA)PF{sub 6} are added to the cell, visual inspection indicates a two-phase system under the conditions used. Near-infrared spectra show that the upper phase is supercritical CO{sub 2} and the lower phase is liquid (THA)PF{sub 6}. This result is obtained at a temperature that is 64{degree}C below the melting point of pure (THA)PF{sub 6} at atmospheric pressure. Ferrocene is found to have a much lower diffusion coefficient in the molten salt. However, the limiting current recorded in the molten salt is not attenuated relative to that in the upper phase, because ferrocene preferentially dissolves in the molten salt. It is shown that the molten salt, when added in small amounts to the cell, acts as an electrode-surface modifier that promotes ionic conductivity and allows the oxidation of ferrocene extracted from the supercritical CO{sub 2}. This occurs even whenmore » the electrode is placed in the upper CO{sub 2} phase.« less