The concentration profiles of Ru(NH3)6 3+ and Ru(NH3)6 2+ as a function of the initial concentration of C2O4 2-(with the concentration of S2O8 2-held constant) were examined to understand why the CV response of a solution containing 0.54 mM Ru(NH3)6 3+ , 1.0 mM S2O8 2-, and 220 mM C2O4 2-closely resembles that of Ru(NH3)6 3+ alone, see Figure . In the absence of S2O8 2-and C2O4 2-, the distance from the working electrode where equimolar concentrations of Ru(NH3)6 3+ and Ru(NH3)6 2+ are present is equal to ~28 µm, as shown by the dotted lines in Figure . Then, in the presence of 1.0 mM S2O8 2-and 1.0 mM C2O4 2-, the point of equimolar Ru(NH3)6 and Ru(NH3)6 2+ shifts toward the working electrode to a distance of ~6 µm (Figure , dashed lines). Upon increasing the C2O4 2-concentration in solution to 220 mM, the concentration profiles of Ru(NH3)6 3+ and Ru(NH3)6 2+ (Figure , solid line) nearly revert back to the profiles obtained in the absence of S2O8 2-and C2O4 2-. We conclude that in solutions containing S2O8 2-and a large excess of C2O4 2-, the self-sustaining S2O8 2-/C2O4 2-autocatalytic reaction cycle is effectively decoupled from the electrode redox reaction (reduction of Ru(NH3)6 3+ ) leading to a voltammetric response that is nearly indistinguishable from that of a solution containing only Ru(NH3)6 3+ . It is worth noting that this observation is consistent with the electrolysis results obtained in Figure , which show that, within the detection limit of the experiment, no S2O8 2-is directly reduced at the electrode when 220 mM C2O4 2-is present in solution. Figure presents additional concentration profile data, including expanded plots for S2O8 .