Voltammetric Characterization of Carbon Paste Electrodes with a Nonconducting Binder. Part I: Evidence of the Influence of Electroactive Species Dissolution into the Paste on the Voltammetric Response

The voltammetric characterization of ferrocene confined within a carbon paste electrode (CPE) with nonconducting binder (Nujol or silicon oil) was performed. The voltammetric behavior depends directly on the way in which the electroactive species were introduced into the paste: as a solid or previously dissolved into the binder. These two forms were found to contribute in the electrochemical process in a single voltammetric peak. Variations in the potential sweep rate, type of binder (meaning changes in ferrocene solubility), the amount of binder in the paste, and also the amount of the electroactive species affect the shape of the voltammetric curves obtained. This enables us to distinguish between the contributions of the solid and dissolved forms of ferrocene in the voltammetric response. From this study, it is established that the ferrocene oxidation in CPE was limited by diffusion, taking place in a layer beyond the electrode–electrolyte interface, resulting from the dissolution of ferrocene within the binder. The existing controversy reported for voltammetric studies of ferrocene in CPE could be explained by the presence of two different ferrocene species involved in the oxidation process.