Isolation of partial coupled processes of anodic oxidation of OH– ion on gold using a combination of a graph-kinetic analysis method and linear voltammetry data

Abstract

The presence of several interconnected electrochemical processes occurring on the surface of an electrode, strictly speaking, does not allow the use of the principle of independent reactions. Often, partial reactions of a complex multi-stage electrochemical process are coupled both through common intermediates and through the competitive adsorption of electroactive species. The presence of conjugation leads either to a change in the potential at which the corresponding electrochemical process becomes possible or to a change in the rate of partial processes. The latter is called kinetic coupling. This does not allow the simple calculation of the rate of each partial reaction as the difference between the current density of the target and background processes. The method of kinetic diagrams can be used to establish the kinetic patterns of such processes. This study shows that this method is applicable not only for the analysis of coupled electrochemical processes of various types, but can also be used in obtaining partial currents of the stages of a separate complex electrode reaction occurring in a background solution. As an example, options for the kinetic modelling of the total voltammogram of the anodic process on an Au electrode in an aqueous alkaline medium in the mode of linear potential change are considered. The stationary degrees of covering of the gold surface with various surface-active forms of oxygen are calculated depending on the electrode potential. It was established that the change in concentration of ОН- ions mainly affects the region of their adsorption potentials. A detailed analysis of stationary partial anodic processes in the Au|OH-,H2O system was carried out and the shape of the general stationary voltammogram was determined by calculation. The latter is in qualitative agreement with the experimental polarization dependence. It was shown that the type of calculated polarization dependence is determined by the degree of reversibility of individual stages and the rate of their occurrence. The performed analysis is necessary not only for the detailed scheme of the background anodic reaction on gold in an alkaline solution, but also for the ubsequent kinetic description of the electrooxidation process of organic substances on a gold electrode

Keywords

• electrode processes
• conjugation
• graphic-kinetic analysis
• adsorption
• voltammetry