Electrochemical investigations of product deposition and dissolution of the reduced forms of alkyl viologens on glassy carbon
The reductions of several alkyl viologens in aqueous solutions at a glassy carbon working electrode were investigated. All of the viologens studied exist as colorless dication salts (V[sup 2+]) which are easily reduced to the violet cation radical (V[sup +.]) by a one electron process. The dications can be reduced directly to the yellow-brown, quinoidal neutral species (V[sup 0]) by a two electron process, or to neutral via the cation radical by two successive one electron transfers. In the absence of sodium n-alkyl sulfates, all but one displayed reversible, diffusion-controlled electron transfers for the V[sup 2+]/V[sup +.] couple. With addition of sodium decyl, undecyl and dodecyl sulfates at concentrations below their critical micelle concentrations (cmc), the cation radical product of methyl and ethyl viologen deposits on the electrode surface. The addition of these surfactants at concentrations below their cmc's precipitated the dicationic species of butyl, benzyl, and heptyl viologens. All redox forms of the viologens are solubilized by the onset of micelles. Double potential step chronocoulometry showed the deposition mechanism to be governed by solubility product equilibria. Open-circuit rotating ring-disk electrode (OC-RRDE) voltammetric experiments revealed that two forms of deposit exist. Above the cmc, little or no deposition of neutral forms occurs as V[sup 0] is solubilized in the hydrocarbon interior of the micelles. Cyclic voltammetric investigations revealed that there are also two forms of deposit for neutral viologens. For heptyl viologen, there may be more than two forms of both the V[sup +.] and V[sup 0] deposits. Deposition of the neutral form is governed by nucleation and subsequent growth. From RRDE voltammetry lower limits of solubility of neutral viologens were estimated. OC-RRDE voltammetric experiments showed that dissolution occurred by extremely fast conproportionation reaction which caused the process to be mass-transfer controlled.
- Research Organization:
- Delaware Univ., Newark, DE (United States)
- OSTI ID:
- 7178091
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400400* -- Electrochemistry
AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CHEMICAL REACTIONS
CHEMISTRY
DEPOSITION
DISPERSIONS
DISSOLUTION
ELECTROCHEMISTRY
HETEROCYCLIC COMPOUNDS
MIXTURES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
REDOX REACTIONS
SOLUTIONS
VOLTAMETRY