In the present work, we used SECM to investigate the kinetics of the elementary steps involved in the homogeneous reduction of S2O8 2-. The electrocatalytic reduction of S2O8 2-via Ru(NH3)6 3+ includes five elementary steps in an aqueous solution. The average rate constant for the homogeneous reduction of S2O8 2-via electrogenerated Ru(NH3)6 2+ was measured to be ~ 5 × 10 5 M -1 s -1 from SSV and ~ 7 × 10 5 M -1 s -1 from SECM measurements. Both values are slightly higher than previous findings based on CV (2 × 10 5 M -1 s -1 ). Our SECM analysis is insensitive to values greater than 1 × 10 6 s -1 for the rate of S2O8 3•-decomposition (i.e., eq. 3), which is also consistent with previous findings. Finally, a lower limit for the rate constant of the reaction between SO4 •-and Ru(NH3)6 2+ was determined as ~ 1 × 10 9 M -1 s -1 using SECM measurements.