Kinetics of Aqueous Polysulfide Solutions: I . Theory of Coupled Electrochemical and Chemical Reactions, Response to a Potential Step

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Abstract
The equations and assumptions that allow the derivation of the analytic form of the current transient for a small potential step are discussed. The equations are generalized so that they are applicable to the electrode reaction: where and are not necessarily equal. Then a system with a homogeneous reaction in solution coupled to the electrode reaction is considered. The treatment includes the case of a solution‐phase homogeneous reaction that takes place at a rate comparable to that of the heterogeneous reaction. The current response to a potential step in the linear overpotential region is solved numerically for both a first‐order homogeneous reaction and a homogeneous reaction involving dissociation‐dimerization. Using this model the exchange current density and diffusion parameter of the heterogeneous reaction can be determined as can the rate constants of the homogeneous reaction. It is shown that there is a range of parameters wherein the electrode current response is most sensitive to the values of the homogeneous rate constants. The results for the two homogeneous kinetic models are qualitatively similar but differ quantitatively.