Cyclic voltammetry emulsion processes

As noted above, cyclic voltammetry is a powerful tool for the investigation of processes combining solution-phase reactions and heterogeneous charge transfer at the electrode surface. However, this technique can also be applied to systems with additional phase boundaries. For example, multi-phase processes in thin films covering an electrode surface (Fig. II. 1.24a), particulate solids, bacteria, or microdroplets attached to the electrode surface (Fig. II. 1.24b), or micro-emulsion systems... 

Emulsion processes are of considerable importance and cyclic voltammetry allows these to be investigated. Texter et al. [23, 121] and Rusling et al. [122] voltammetrically studied processes in optically clear, stabilised microemulsions, in which the droplet size was smaller than 100 nm. Processes monitored were shown to be consistent with a CE-type reaction scheme in which reactant diffused from the organic emulsion droplet towards the electrode surface. 

Many useful synthetic reactions cannot be carried out electrochemically because of the passivation of the electrode by the starting materials, reaction intermediates, or products [8, 11]. One possible solution is the ultrasound-induced formation of emulsions from biphasic systems so that the electrode process of interest occurs in the aqueous phase but the organic component constantly dissolves and removes the electrode passivating species. An example is the electroreduction of MG (see Fig. 8). MG is soluble in water, but the product of its two-electron reduction, 1-MG, is not (19, 35]. Silent cyclic voltammetry of a 0.2 mM solution of MG in... 

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