Kinetics of Aqueous Polysulfide Solutions: II . Electrochemical Measurement of the Rates of Coupled Electrochemical and Chemical Reactions by the Potential Step Method

Abstract

The kinetics of the aqueous polysulfide redox couple were investigated using a potential step technique in a solution 1M in S⁰ and 1.3M in total S²⁻, at pH 12. The low overpotential region (−20 to +20 mV) on cobalt and platinum electrodes was investigated from 25° to 80°C. The active species concentration was found to be several orders of magnitude lower than those of any of the major (poly)sulfide ions, and its temperature dependence corresponded to an of about 10 kcal/ mol. These results are consistent, with the active species being . Deviations were found at temperatures above 45°C between experimental data and the simple analytical form for the current response for an electrode reaction with one rate‐determining step. The results agree with a new model that considers two rate‐determining steps, one of which is the reaction . The rate constants for this reaction determined using this new model agree with those measured for similar reactions.