Abstract
We introduce dual kinetic chronoamperometry, in which reciprocal relations are established between the kinetic curves of electrochemical reactions that start from symmetrical initial conditions. We have performed numerical and experimental studies in which the kinetic curves of the electron-transfer processes are analyzed for a reversible first order reaction. Experimental tests were done with the ferrocyanide/ferricyanide system in which the concentrations of each component could be measured separately using the platinum disk/gold ring electrode. It is shown that the proper ratio of the transient kinetic curves obtained from cathodic and anodic mass transfer limited regions give thermodynamic time invariances related to the reaction quotient of the bulk concentrations. Therefore, thermodynamic time invariances can be observed at any time using the dual kinetic curves for reversible reactions. The technique provides a unique possibility to extract the non-steady state trajectory starting from one initial condition based only on the equilibrium constant and the trajectory which starts from the symmetrical initial condition. The results could impact battery technology by predicting the concentrations and currents of the underlying non-steady state processes in a wide domain from thermodynamic principles and limited kinetic information.
Highlights
Onsager relationships [1,2,3] are widely used for extracting of detailed information about reciprocal processes
We designed a series of experiments in which the theoretically developed technique for dual kinetic chronoamperometry can be validated in a single electron transfer reversible reaction, the oxidation of ferrocyanide to ferricyanide ions
Reciprocal relations between the kinetic curves provide a unique possibility to extract the non-steady state trajectory starting from one initial condition based only on the equilibrium constant and the trajectory which starts from the symmetrical initial condition
Summary
Onsager relationships [1,2,3] are widely used for extracting of detailed information about reciprocal processes. The presence of such manifold is a characteristic nature of reactions systems with time-scale separation; in this example the reaction timescale (related to the inverse of rate constant) is smaller than the diffusion timescale (proportional to the inverse of the diffusion constant). A convenient way of generating of two symmetrical initial conditions is to pre-polarize the electrode at high anodic and cathodic potentials where the mass-transfer limited reactions fully consume one of the reactants
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