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.