the rate constant was found to decrease, which might be because water oxidation inhibited the hypochlorite formation. This effect was not observed when KNO3 was used as supporting electrolyte in place of KCl. In the presence of KNO3, decolorization rate was sufficiently low throughout the potential range. This observation indicates that at potentials higher than +0.6 V at the working electrode, hypoclorites were generated that caused chemical oxidation of MB molecules in the presence of KCl.