Electro-oxidation of chlorophenols at a gold electrode

The electrooxidation of chlorophenols (CPs) with one to five chlorine atoms at gold electrodes was studied by cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM). The results obtained indicate that the oxidation of CPs at gold electrodes depends on the pH, the phenol concentration, the number of chlorine atoms in the aromatic ring, and the position of these Cl atoms with respect to the phenolic OH. At low scan rates and/or high CP concentrations, for mono- and di-CPs the phenoxi radicals condense forming polymers, or at least oligomers, that precipitate at the electrode surface, the resulting film behaving as an insulator that passivates the gold electrode. On the contrary, at high potential scan rates and/or low CP concentrations the film can be porous enough for charge transfer to continue. (C) 2001 Elsevier Science Ltd. All rights reserved.