Effect of platinum oxide on electro-oxidation of trace amounts of sodium hypochlorite in aqueous medium

The electro-oxidation mechanism of trace amounts of sodium hypochlorite (< 4.0 mg Cl dm(-3)) in an aqueous medium has been studied by employing the potential sweep method and double-potential step chronocoulometry. These methods confirmed the occurrence of the competition reaction of the Faradaic-based hypochlorite and the non-Faradaic-based formation of platinum oxide. In the hypochlorite-free solution, the amount of platinum oxide formed during the non-Faradaic reaction was approximately 1.3 pmol cm(-2); however, with an increase in the amount of sodium hypochlorite, the amount of platinum oxide gradually decreased to approximately 0.2 pmol cm(-2). The results of this study suggest that the electro-oxidation of trace amounts of hypochlorite, particularly amounts less than 1.0 mg Cl dm(-3), is strongly inhibited by the initial formation of platinum oxide in a non-Faradaic reaction. (C) 2008 Elsevier B.V. All rights reserved.