Aqueous solutions containing both the oxidant, peroxydisulfate (S2O82-), and reductant, oxalate (C2O42-), are thermodynamically unstable due to the highly exothermic homogeneous redox reaction, S2O82- + C2O42- ® 2SO42- + 2CO2. However, at room temperature, the reaction does not occur to any significant extent due to slow electron-transfer kinetics. We demonstrate that the S2O82-- C2O42- redox reaction can be initiated by electrochemical injection of an electron to generate S2O83-, which then undergoes bond cleavage to form the highly oxidizing SO4-. The SO4- then oxidizes C2O42- to generate CO2 and the highly reducing CO2-. In turn, CO2- then reduces another molecule of S2O82- to S2O83-, resulting in a self-sustaining cyclic redox that consumes both S2O82- and C2O42-. Theoretically, a single electron is capable of initiating the homogeneous process. Using outer-sphere redox mediators (e.g., Ru(NH3)63+/2+) as electrocatalysts to initiate the reaction, we show that, within error of the measurement, the reaction becomes self-sustaining with the injection of a single electron.

Peroxydisulfate-oxalate ping-pong reaction

ACS Spring 2022

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