INVESTIGATION OF THE NATURE OF ELECTRODEPOSITED NEUTRAL VIOLOGENS FORMED BY REDUCTION OF THE DICATIONS

Reduction of four viologens was studied in aqueous media at glassy carbon working electrodes. The viologens were the methyl (MV2+), ethyl (EV2+), benzyl (BV2+) and heptyl (HV2+) derivatives. The neutral two-electron reduction product of each viologen forms an insoluble deposit on the electrode surface. The formation of these deposits was studied by cyclic voltammetry, rotating ring-disk electrode voltammetry (RRDE) and double potential step chronocoulometry (DPSC). RRDE studies of MV2+ reveal that the neutral form becomes supersaturated in solution near the disk surface. The deposition is initiated by a nucleation and growth phenomenon. As the deposit grows, blockage of the disk surface occurs and the disk current decreases. Reaction of MV2+ with the deposit (conproportionation) becomes increasingly important and the amount deposited shows a net decrease followed by an approach to a steady state. The steady state amounts deposited have been determined by step and open circuit experiments with RRDE and, at early stages, by DPSC.