Anodic and cathodic modification of glassy-carbon electrodes affect iodine electrochemistry

The effect of electrochemical oxidation and reduction of the surface of a glassy carbon (GC) electrode on the redox reaction of iodide ions (I-) in aqueous solution was investigated. The mechanism was also analyzed on the basis of the results of spectroscopic analyses. When a GC electrode was electrochemically oxidized in an aqueous solution, the carbon on the GC surface was transformed to a functional group, and the redox reaction activity of I- on the GC electrode was significantly decreased. This is presumably because transformation decreases the number of reaction sites at which I- are adsorbed. The functional groups on the oxidized GC were electrochemically reduced in an aqueous solution, and the redox reaction activity of I- was restored and further improved in comparison with the activity of the GC before oxidation. It is possible that the recovery of the redox reaction activity of I- was derived from the restoration of reaction sites on the GC. The reaction site of I- is considered to be carbon in the graphite structure with the pi orbital or carbon adjacent to a defect in the diamond structure. Spectroscopic analyses revealed that the ratio of the graphite structure to diamond structure increases, and defects in the diamond structure become more abundant on the GC reduced after oxidation. The increase in the number of reaction sites is considered to enhance the redox reaction activity of I- on the GC reduced after oxidation. (C) 2021 Elsevier Ltd. All rights reserved.