Kinetics and mechanism of the oxidation of sodium dithionite at a platinum electrode in alkaline solution

摘要

In this paper the oxidation of sodium dithionite in alkaline solution was studied by cyclic voltammetry at a stationary and rotating platinum disk electrode. The reaction proceeds in two steps, with sulfite as a relatively stable intermediate and sulfate as final product. It was possible to quantitatively analyze the kinetics of the oxidation wave making use of the experimental evidence that the reaction rate is not dependent on pH, with a reaction order of 0.5 with respect to sodium dithionite and a charge transfer coefficient of 0.5. The proposed mechanism of the overall electron transfer reaction consists of five consecutive steps starting with the adsorption of dithionite, followed by decomposition into SO_2~-, which releases an electron in the rate determining step and finally two more chemical steps leading to the formation of sulfite. The predicted behavior by this mechanism is in agreement with the experimentally observed one.