Halogenate electroreduction fromacidic solution at rotating disc electrode. Maximal steady-state convective-diffusion current for comparable concentrations of halogenate ions and protons

Vorotyntsev, M.A.; Zader, P.A.

Авторы: Vorotyntsev Mikhail A., Zader Pavel A.
Журнал: Journal of Electroanalytical Chemistry
Том: 939
Год издания: 2023
Издательство: Elsevier Sequoia
Местоположение издательства: Switzerland
Первая страница: 117331
DOI: 10.1016/j.jelechem.2023.117331
Аннотация: Process of electrochemically inactive halogenate-anion (XO3-, X = halogen) electroreduction at rotating disk electrode (RDE) under steady-state conditions via a mediator cycle: XO3- + 5 X- + 6H+ → 3 X2 + 3 H2O in solution (*), X2 + 2 e- ⇄ 2 X- on electrode surface in acidic aqueous medium has been analyzed theoretically on the basis of a set of coupled convective-diffusional transport equations for predicting the dependence of its rate on numerous parameters of the system, without application of expensive commercial software for its numerical integration. Approximate solution of these equations for the concentration distributions of all reactive species (halogenate and halide anions, halogen molecules and protons), as well as for the maximal current, as functions of the RDE frequency, bulk-solution concentrations of XO3-, X2 and H+ species, diffusion coefficients of all reactive components, rate constant of comproportionation reaction (*), kinematic viscosity of solution, etc., is given as a simple analytical procedure which provides this solution in the numerical form for any set of values of these parameters. These characteristics of the process are determined primarily by the ratio of the diffusion (for species X2) and kinetic layer thicknesses: xdkC = zdC / zk, which depends on the RDE frequency and the bulk-solution concentrations of species XO3- (Ao) and H+ (Ho), as well as on other parameters of the system. Weak-current regime takes place for its relatively small values: xdkC < 6, i.e. for sufficiently high RDE frequencies, where the maximal current is proportional to the bulk-solution concentration of X2 molecules, Co, being independent of the Ao and Ho concentrations. Within the opposite range of this parameter: xdkC>6, i.e. for sufficiently low RDE frequencies, the maximal current is comparable to the smaller of the diffusion-limited currents of XO3- and H+ species, jAlim and jHlim, being practically independent of the Co concentration. This strong-current regime which does not exist for the conventional EC-cat (or EC') mechanism is entirely due to the autocatalytic feature of the mediating redox cycle (EC-autocat mechanism) which may lead to enormous accumulation of the X2/X- redox couple components near electrode surface.Keywords: Halogen/halide redox mediation; Halogenate-halide-proton comproportionation reaction; Autocatalytic cycle; Convective transfer; Diffusion-limited currents; Weak- and strong-current regimes
Добавил в систему: Задёр Павел Александрович

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Halogenate electroreduction fromacidic solution at rotating disc electrode. Maximal steady-state convective-diffusion current for comparable concentrations of halogenate ions and protonsстатья