Mechanism of the Br-/Br2 Redox Reaction on Platinum and Glassy Carbon Electrodes in Nitrobenzene by Cyclic Voltammetry

We report the determination of a complete mechanism for the Br-/Br-2 reaction in nitrobenzene using simulations of cyclic voltammograms at platinum and glassy carbon macroelectrodes and platinum ultramicroelectrodes at varying scan rates 90.02-500 V/s) and concentrations of Br-, Br-3(-), and Br-2 92.5-20 mM). As in other nonaqueous solvents and ionic liquids, we observe two consecutive redox processes at lower and higher potentials that we assign to the Br-/Br-3-and Br-3(-)/Br-2 redox reactions, respectively. A complete reaction mechanism, including the elementary steps of each process, was fit to the voltammetric data using DigiElch((R)) simulation software. The model proposed here is different from previous models of halide reactions in nonaqueous solvents in three ways. First, it proposes the direct oxidation and reduction of Br-3(-), whereas previous models describe the reduction and oxidation of X(3)(-)as a CE process, with the dissociation of X-3(-) into X-and X-2 occurring first. Second, it is able to accurately match data at a wide range of scan rates and concentrations without the use of unrealistically large homogeneous rate constants. Finally, it can match data at platinum and glassy carbon electrodes by simply changing the apparent heterogeneous kinetics of the electron transfer reactions. (C) 2016 Elsevier Ltd. All rights reserved.