Scanning Electrochemical Microscopy in Nonusual Solvents: Inequality of Diffusion Coefficients Problem

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• 作者：Jalal Ghilane ; Corinne Lagrost ; Philippe Hapiot
• 刊名：Analytical Chemistry
• 出版年：2007
• 出版时间：October 1, 2007
• 年：2007
• 卷：79
• 期：19
• 页码：7383 - 7391
• 全文大小：236K
• 年卷期：v.79,no.19(October 1, 2007)
• ISSN：1520-6882

文摘

Scanning electrochemical microscopy offers interestingpossibilities for investigating both transport properties inroom-temperature ionic liquids (RTILs) and reactionsoccurring at the ionic liquid/substrate interface. Besidesthe expected difficulties related to the lower diffusioncoefficients for species dissolved in RTILs arising fromthe higher viscosity of RTILs, the major problem comesfrom the inequality of the diffusion coefficients betweenthe oxidized and reduced forms of the redox mediatorused to probe the interfaces. This question was treatedby an extension of the model originally presented byMartin and Unwin (Martin, R. D.; Unwin, P. R. J.Electroanal. Chem. 1997, 439, 123) and was adaptedto the specific aspects of SECM in ionic liquids. Theinequalities of diffusion coefficients lead to large anomalies in the current responses, which in extreme casesimpede the recording of stationary approach curves.Conditions for recording steady-state approach curves intoionic liquids and consequences of erroneous data treatment were examined. These discrepancies with the simplemodels (when diffusion coefficients have been taken asequal), could be transformed in a convenient method forcharacterizing the transport properties of species dissolved in RTIL. The analysis is based on transient SECMexperiments and determinations from nonambiguousdimensionless parameters. Experimental examples basedon SECM in common RTILs, using the O₂/ O₂^- couple,were analyzed taking into account the presented model.