). The reversible CV response obtained in a 0.5 mM Ru(NH3)6 3+ solution is shown in Figure , black trace. In contrast, in the presence of 1.0 mM S2O8 2-, a large irreversible voltammogram is observed that is associated with the catalytically mediated reduction of S2O8 2-by electrogenerated Ru(NH3)6 2+ , resulting in regeneration of Ru(NH3)6 3+ and the generation of S2O8 3•- , Figure , red trace. This irreversible CV response has been described in a prior report and is ascribed to a five-step EC'CEC mechanism (eqs 17, 18, 8, 9, and 19). Values of kf 18 and kf have been previously reported and are based, respectively, on CV and scanning electrochemical microscopy analyses, while kf 8 was estimated from DFT predictions. Detailed simulations of this mechanism demonstrated that electrogenerated Ru(NH3)6 2+ reduces S2O8 2-in solution (eq 18)