The bromine electrode Part II: reaction kinetics at polycrystalline Pt

Abstract

The kinetics of bromide oxidation and Br 3 ) reduction were studied at polycrystalline Pt electrodes in acidic media. The electrochemical behavior of equimolar Br 3 ) and Br ) solutions was investigated, in a concentration range of the electroactive species between 0.1 and 1.0 M. E-log j plots did not exhibit linear segments, most probably because of extensive adsorption of bromine radicals. Further analysis supported the hypothesis of a Volmer-Tafel mechanism, with the chemical recombination step as rate determining. Electrosorption isotherms for Br radicals were found to be of the Frumkin type. The kinetics of Br 3 ) reduction was controlled by the surface dissociation of the Br 2 molecules.

The bromine electrode Part III: reaction kinetics at highly boron-doped diamond electrodes

“…A similar analysis was tentatively carried out on the bromine electrode data obtained at the polycrystalline Pt [7]. In that case, however, the CV investigation showed a complex behavior: as expected, the system is not as irreversible as in the present case, but not Nernstian (perfectly reversible) either.…”

“…CV data for three different reactant concentrations (1, 5 and 10 mM Br ) /Br 3 ) ) are shown in Figure 1 and, as expected, they differ significantly from the signals obtained at polycrystalline Pt [7]. In particular, the kinetics are slower at BDD, as indicated by the larger DE p and the lower peak current densities.…”

“…presents new insights into the reaction mechanism, in connection with the possible interference of concomitant oxygen evolution reaction intermediates. A previous paper of ours [7], on the other hand, supplies further information on the subject, especially due to the simultaneous presence of both the partners of the redox couple.…”

“…Details on solution preparation were given in [7]; in all cases, the test solution was adjusted to a pH of 2 with perchloric acid, and a constant ionic strength (also equal to 2) was maintained, by adding the appropriate amount of sodium perchlorate. In addition to the BDD film, which was placed at the bottom of the electrochemical cell [5], a low-porosity graphite cylinder and the abovedescribed SCE were used as the counter and the reference electrodes, respectively.…”

The occurrence of bromate and perbromate on BDD anodes during electrolysis of aqueous systems containing bromide: first systematic experimental studies

“…Ferro and co-workers studied the kinetics of Br -and Br 3 -oxidation on Pt [27]. In dealing with BDD anodes, Ferro concluded that bromide oxidation is mass transfer-controlled [28].…”