KINETIC-STUDY OF OXYGEN REDUCTION IN ETHA NOL-WATER MIXTURES ON GRAPHITE-ELECTRODES IN TERMS OF MARCUS THEORY

Oxygen reduction on a highly oriented pyrolytic graphite in water-etha nol mixtures was studied by the rotating disk techniques. For ethanol concentrations between 15 and 50 v%, the current decreases progressive ly, which is associated with a gradual reduction in the ionic conducti vity of the solution as the ethanol content increases. However, for et hanol concentrations between 50 and 75 v%, a sudden change in the curr ent associated with oxygen is observed, the current increases and a di splacement of the current maximum takes place. Relating the electroche mical data to Marcus's theory, such a behaviour is associated with a c hange from an inner-sphere to an outer-sphere mechanism. Further, in t he kinetic interpretation, the role of the reorganizational energy is analyzed.