Advantages Available in the Application of the Semi-Integral Electroanalysis Technique for the Determination of Diffusion Coefficients in the Highly Viscous Ionic Liquid 1-Methyl-3-Octylimidazolium He

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• 作者：Cameron L. Bentley ; Alan M. Bond ; Anthony F. Hollenkamp ; Peter J. Mahon ; Jie Zhang
• 刊名：Analytical Chemistry
• 出版年：2013
• 出版时间：February 19, 2013
• 年：2013
• 卷：85
• 期：4
• 页码：2239-2245
• 全文大小：325K
• 年卷期：v.85,no.4(February 19, 2013)
• ISSN：1520-6882

文摘

While it is common to determine diffusion coefficients from steady-state voltammetric limiting current values, derived from microelectrode/rotating disk electrode measurements or transient peak currents at macroelectrodes, application of these methods is problematic in highly viscous ionic liquids. This study shows that the semi-integral electroanalysis technique is highly advantageous under these circumstances, and it has allowed the diffusion coefficient of cobaltocenium, [Co(Cp)₂]⁺ (simple redox process), and iodide, I^{鈥?/sup> (complex redox mechanism), to be determined in the highly viscous ionic liquid 1-methyl-3-octylimidazolium hexafluorophosphate (viscosity = 866 cP at 20 掳C) from transient voltammograms obtained using a 1.6 mm diameter Pt electrode. In such a viscous medium, a near-steady-state current is not attainable with a 10 渭m diameter microdisk electrode or a 3 mm diameter Pt rotating disk electrode, while peak currents at a macrodisk are subject to ohmic drop problems and the analysis is hampered by difficulties in modeling the processes involved in the oxidation of iodide. The diffusion coefficients of [Co(Cp)₂]+ and I鈥?/sup> were determined to be 9.4 (卤0.3) 脳 10鈥? cm2 s鈥? and 7.3 (卤0.3) 脳 10鈥? cm2 s鈥?, respectively. These results highlight the utility of the semi-integral electroanalysis technique for quantifying the diffusivity of electroactive species in high viscosity media, where the use of steady-state techniques and transient peak currents is often limited.}