DEMS analysis unambiguously demonstrates that the S2O8 2-/C2O4 A detailed mechanistic analysis was performed using DFT and AIMD simulations, which further guided FD simulations of experimental CV data. Based on activation energy barriers computed from DFT, we conclude that the reduction of S2O8 2-by CO2 •-, which is accompanied by a high inner-sphere reorganization energy, must be slower than the oxidation of C2O4 2-by SO4 •-, a conclusion supported by prior pulse radiolysis studies. In agreement with this conclusion, FD simulations of the experimental CVs show that the S2O8 2-/C2O4 2-autocatalytic reaction proceeds via the reduction of Ru(NH3)6 3+ by CO2 •-followed by the reduction of S2O8 2-by Ru(NH3)6 2+ (eq 24 followed by eq 18) rather than by the reduction of S2O8 2-by CO2 •-(eq 16).