Generalized Nernst Layer Model: Application to Bromate Anion Electroreduction and Theory for the Stationary 1D Regime of Proton Transport Limitations

Abstract

International audienceTheoretical analysis has been developed for the reduction process of the non-electroactive bromate anion through an autocatalytic cycle composed of the reversible Br-2-to-Br- transformation and the irreversible (owing to high acidity of the solution) comproportionation reaction. Owing to the autocatalytic character of this redox-mediating cycle (EC mechanism) even a tracer amount of Br-2 in the bulk solution may result in enormous values of the reduction current, which are determined by the diffusion-limited flux of either bromate anions or protons. The latter case has been analyzed in this study within the framework of the generalized Nernst layer model, which takes into account the non-equality of the diffusion layer thicknesses for H+, Br-, and Br-2 species because of the difference in their diffusion coefficients, as evident from the Levich formula for the rotating disk electrode (RDE). Approximate analytical expressions for all characteristics of the system have been derived for two regimes corresponding either to weak currents or to a thin kinetic layer. In particular, the maximal current for the diffusion-limited conditions turned out to depend on the ratio of the diffusion layer thicknesses for H+ and Br-2, that is, of their diffusion coefficients

Novel Aqueous Zinc–Halogenate Flow Batteries as an Offspring of Zinc–Air Fuel Cells for Use in Oxygen‐Deficient Environment

“…Bromate reduction mechanism was considered theoretically for different configurations of the electrodes under convective diffusion transport of reactants. [ 48–53 ] The EC’’ notation was proposed for this particular reduction mechanism.…”

Redox-Mediated Bromate Based Electrochemical Energy System

“…[23][24][25][26] The first study of the EC' mechanism for battery application was conducted by Tolmachev and his colleagues with bromate ion. 9,[27][28][29][30][31][32][33] The bromate ion, which is a bromine-based oxoanion, in aqueous acidic solution is supplied to the cathode side of the cell while hydrogen gas is provided to the anode side during cell operation. The bromate ion does not undergo electrochemical reaction directly due to its inactivity at the carbon electrode.…”

“…Tolmachev and his colleagues 9,[27][28][29][30][31][32][33] extensively investigated the bromate system through research combined with experiment and theoretical analysis to understand the characteristic behavior of the coupled electrochemical reactions. They utilized the concept of kinetic layer (z k ) and diffusion layer thickness (z d ) to understand the relative effect of electrochemical reaction and chemical reaction rates in rotating disk electrode (RDE) experiment, and defined the conditions to induce the normal or abnormal behaviors.…”