RAPID OXIDATION OF RU(NH3)(6)(3+) BY OS(BPY)(3)(3+) WITHIN NAFION COATINGS ON ELECTRODES

The oxidation of Ru(NH3)(6)(3+) by Os(bpy)(3)(3+) is a very slow proce ss in aqueous acid. The rate increases with pH but the reaction remain s slow at pH 7. However, when the two reactants are incorporated in Na fion coatings on electrodes the oxidation can proceed much more rapidl y, especially with Nafion coatings that are not fully hydrated. Rotati ng disk and cyclic voltammetry were employed to determine the stoichio metry of the reaction and to measure its kinetics both in solution and in Nafion coatings. The Ru(NH3)(6)(3+) is oxidized to Ru(VII) at a ra te that is first order in Ru(NH3)(6)(3+) and Os(bpy)(3)(3+) and invers e first order in H+. The reaction rate constant evaluated in solution was similar to that evaluated in Nafion, The higher reaction rate obta ined when the reactants are incorporated in Nafion results from their higher concentrations, not from significant enhancement of their react ivities. The higher reaction rate obtained from partially dehydrated N afion coatings is believed to result from a breakdown in cation permse lectivity that permits the ionic current inside the coating during ano dic current flow to be carried by anions instead of by the ejection of Ru(NH3)(6)(3+) cations from the Nafion.