Electrochemical Study of Bi[sub 2]O[sub 3] and Bi[sub 2]O[sub 2]CO[sub 3] by Means of a Cavity Microelectrode. I. Observed Phenomena and Direct Analysis of Results

Abstract

The physical and chemical processes occurring for the electrochemical reduction and oxidation of and can be determined through a direct analysis of the voltammograms recorded from the cavity microelectrode. The voltammogram shows an evolution for around 1 h, which corresponds to the first 80 cycles carried out at . The evolution is due to the sequence of the following concurrent processes: (i) impregnation of the powder and its dissolution in the electrolytical solution, (ii) deposit of porous metal‐Bi during the cathodic scan, and deposit of Bi(III) species during the anodic scan. These processes cause a reconfiguration of the architecture of the powder within the cavity by making the material grains smaller. For the second stage, the voltammograms do not vary any more during the cycling. For the first cathodic scan, the reduction process starts from the bottom of the cavity at the interface Pt/solution only, then it progresses toward the mouth. Contrarily, the oxidation takes place throughout all the grains. During the next cathodic scans, the reduction also starts throughout all the grains when the grains are not entirely oxidized from the preceding anodic scan. © 2000 The Electrochemical Society. All rights reserved.