Voltammetry study of Cr(III)/Cr(II) system in aqueous methanesulfonate solutions

Abstract

In this paper, some electrochemical and spectral parameters of Cr(III) methanesulfonate (MS) complexes were investigated. Trivalent chromium ions were stated to exist in methanesulfonate aqueous solutions both in a violet form and in a green one. The kinetic parameters of one-electron Cr(III) electroreduction in methanesulfonate electrolytes were determined by means of cyclic voltammetry on the lead, cadmium and tin electrodes. The Cr(III) electroreduction process was shown to be irreversible in electrolytes containing methanesulfonic acid (MSA). The standard discharge rate constants of Cr(III) complexes diminish in the following sequence: Cr(ClO4)3 (aqua-complex)–CrCl3 (violet form)–Cr(MS)3 (violet form)–Cr(MS)3 (green form)–Cr2(SO4)3 (green form). This sequence coincides with that in which the wavelengths of the absorption peaks, the absorption intensities and cross sections of the particles increase. The electroreduction of Cr(III)–MSA complexes proceeds via an outer-sphere mechanism. The standard rate constant of the Cr(III) complexes discharge is practically independent of the nature of the electrode.