Figure shows that the electrochemical reduction of Ru(NH3)6 3+ is reversible, occurring near E 0 for the Ru(NH3)6 3+/2+ couple, while the electrochemical reduction of S2O8 2-is kinetically sluggish and requires a large overpotential. In line with the kinetics of these electrode reactions, calculations from Marcus theory show that when CO2 •-is employed as the electron source, Ru(NH3)6 3+ reduction occurs with a low free energy barrier of ∆𝐺 ǂ = 5 𝑘𝐽/mol as compared to S2O8 2-reduction, which has a free energy barrier of ∆𝐺 ǂ = 43 𝑘𝐽/mol. The low energy barrier for eq 24 suggests that Ru(NH3)6 3+ reduction by CO2 •-should be a relatively fast reaction, a result used below in the simulations of the cyclic voltammetric behavior. The higher barrier for CO2 •- reduction of S2O8 2-, eq 16, can be attributed to the high inner-sphere reorganization energy of λ i = 416 kJ/mol associated with the reduction of S2O8 2-to S2O8 3-• , as there are appreciable structural changes that result from the elongation and dissociation of the peroxo bond.