A new electrocatalytic mechanism for the oxidation of phenols at platinum electrodes Silvana Andreescu, Daniel Andreescu, Omowunmi A. Sadik * Department of Chemistry, State University of New York at Binghamton, P.O. Box 6000, Binghamton, NY 13902-6000, USA Received 2 June 2003; received in revised form 19 June 2003; accepted 19 June 2003 Published online: 9 July 2003 Abstract Electrochemical oxidation of phenolic compounds generally produces unstable phenoxy radicals that readily polymerize to passivate the surface of solid electrodes. In this study, the electrocatalytic oxidation of phenol in the presence and absence of methanol was investigated by cyclic voltammetry on a platinum electrode. The cyclic voltammogram of phenol in a mixture of phosphate buffer/methanol solution showed well-defined peaks at 600 mV vs. Ag/AgCl reference electrode, which surprising, gradually increased with repetitive scanning, stabilizing after 50 cycles. This unexpected behavior is in contrast to previous studies involving phenolic compounds, which always show a decrease in intensity during continuous potential scanning. Scanning elec- trochemical spectroscopy (SEM) was further used to investigate the changes in the surface morphology of the Pt electrode after electrodeposition. A new electrocatalytic mechanism for phenol oxidation on the surface of a Pt electrode is suggested in the presence of methanol. The proposed mechanism is based on the formation of a film of Pt oxide/hydroxides onto which the phenol and the products of its electrochemical oxidation are further deposited. The mechanism was also studied using more complex phenolic compounds including resveratrol, quercetin and bisphenol A. The results emphasized the effect of aryl substituents on the electrochemistry of this particular class of compounds. Ó 2003 Published by Elsevier B.V. Keywords: Phenol; Electrocatalytic oxidation; Cyclic voltammetry; Pt; Methanol 1. Introduction For decades, the determination and characterization of phenolic compounds have received considerable at- tention due to their importance in environmental, food and industrial processes. Although the electrochemistry of phenol and phenolic compounds has been studied intensively, several mechanistic aspects when working in different experimental conditions are still unclear. Gen- erally, the oxidation of phenolic compounds produces unstable phenoxy radicals that can be further oxidized to quinones or can react to form dimers, which readily polymerize into a polyaromatic compound [1–4]. The phenoxy radicals can interact with each other or with another phenol monomer to give rise to a strongly ad- herent insulating film that passivates the surface of the working electrode [2–4]. This property has been used for the protective coat- ing of metals in order to solve the problems of corrosion [5]. At the same time intensive studies have been per- formed in order to protect the electrode surface against passivation [6] or to even remove this strongly adherent polymer film [7,8]. These processes are important for the treatment of phenolic effluents and have a direct impact for environmental protection. Numerous treatment techniques have been developed to overcome the prob- lems of surface fouling, particularly in wastewater [8,9]. These include biological, chemical or electrochemical treatment, none of which have completely solved the problems related to this unwanted phenomenon. The electrochemical treatment of electrode surface has been shown to reduce fouling [6]. For instance, the use of higher applied potentials combined with a lower initial concentration of phenol in acidic medium (pH 2.2) were Electrochemistry Communications 5 (2003) 681–688 www.elsevier.com/locate/elecom * Corresponding author. Tel.: +1-607-777-4132; fax: +1-607-777- 4478. E-mail address: osadik@binghamton.edu (O.A. Sadik). 1388-2481/$ - see front matter Ó 2003 Published by Elsevier B.V. doi:10.1016/S1388-2481(03)00166-8