Electrochemical Study of Metallic Rhenium in Methanol Acidic Aqueous Solutions

Abstract

Cyclic voltammograms were performed in a window potential from -0.4 to 1.6 V, in solutions of a) H2SO4 0.5M, b) CH3OH 2 M + 0.5 M, c) HCl 0.145 M, d) CH3OH 2 M + HCl 0.145 M. In the sweeps towards anodic direction a soluble oxide is formed at potential superior to 1 V, which is electrodeposited in the sweeps towards cathodic direction. The electrodeposited surface is formed by Re(I) and Re(0) and anodic peaks (0.47 V and 0.71 V vs SHE) correspond to the formation of higher oxidation states (Re(I)→Re(II)→Re(VI)). Methanol affects the structure of anodic peaks separately of the presence of ions chlorides or sulfates. In both acids the soluble oxide is formed and also this specie is produced in sulfuric acid solutions with methanol. Contrariwise, in hydrochloric acid solutions with methanol the perrhenate is the predominant specie. We suggest new hydrogen bonding structures in this solution. Furthermore, we propose a new bonding structure when methanol is dissolve in sulfuric acid or hydrochloric acid solutions. This specie produces bands at 317 nm or 321 nm in the UV-visible spectra of soluble oxide. The high corrosion of metallic rhenium impedes its use as an anode for methanol electrooxidation