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Electrochemical thermodynamics and kinetics in nonaqueous systems

Efrain Castro Narro, University of Nebraska - Lincoln

Abstract

A variety of advantages can be offered by nonaqueous solvents. For example, they are essential for compounds that are unstable or insoluble in water, they can offer a larger potential window before the electrolysis of the solvent occurs, they provide a wide range of solvent environments, they are promising for laboratory scale synthesis and they have proven to be good solvents for various applications including high energy batteries. However, a difficulty with nonaqueous solvents is the choice of a reference electrode in terms of comparing data obtained in various solvents and problems involving the choice and preparation of liquid junctions. Three main investigations were performed. ^ First, the activity coefficients of several 1:1 electrolytes in acetonitrile and of a 1:1 electrolyte in water have been estimated using the isopiestic technique. Osmotic coefficient data were fit using the Pitzer equation and the resulting fitting parameters were used to calculate activity coefficients. ^ Second, nonaqueous electrochemical cells such as the one below, were examined Ag∣X MAgClO4 ∥YM TBAClO4∣poly- Ruvbpy3 ClO4 n∣Pt a b where “::” denotes an anion exchange membrane. ^ A particularly useful set of conditions is present when the perchlorate activities in the α and β phases are equal. Under these conditions the liquid junction potential approaches zero. Such a cell could be used as a reference electrode over a broad range of supporting electrolyte concentrations in acetonitrile to deconvolute voltammetric measurements of the formal potentials. The results from this electrochemical cell were applied to study the use of redox couples such as ferrocene/ferrocenium as internal standards, finding that there is an extensive ion-pairing associated with the oxidized forms of both couples. ^ Third, the use of a well-described polymer-modified electrode surface to better understand electrochemical cell potential measurements in acetonitrile is demonstrated using the junction-less electrochemical cell Ag∣X MAg+ CH3CN, XMPF 6-CH3 CN∣poly- Ruvbpy 3PF6 n∣Pt where vbpy is 4-methyl-4-vinyl-2,2-bipyridine, n = 2 or 3. ^ This system was also Nernstian in water. The cell potentials measured in acetonitrile are +0.303 V of those measured in water. This offset in cell potentials suggested that there is significant solvation of the PF6 ions of the polymer itself in one or both solvents. ^ The fourth chapter describes the synthesis of several molecules with multiple redox sites in their structure. Molecules were designed to direct electron transfer at electrode surfaces. ^

Subject Area

Chemistry, Analytical

Recommended Citation

Castro Narro, Efrain, "Electrochemical thermodynamics and kinetics in nonaqueous systems" (2001). ETD collection for University of Nebraska - Lincoln. AAI3034368.
http://digitalcommons.unl.edu/dissertations/AAI3034368

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