STUDY OF A COBALT-BASED SURFACE-MODIFIED GLASSY-CARBON ELECTRODE - ELECTROCATALYTIC OXIDATION OF SUGARS AND ALDITOLS

Sugars and alditols undergo an electrocatalytic oxidation in alkaline solution at cobalt-oxide-based glassy carbon (Co/GC) electrodes. The c atalytic deposit was investigated by cyclic voltammetry and scanning e lectron microscopy (SEM). It is pointed out that, at relatively low co verage of cobalt, two main redox processes, Co-II --> Co-III and Co-II I --> Co-IV, are observed in 0.2 M NaOH. The redox behavior of the Co/ GC electrode is strongly dependent on hydroxide ion concentration, and no electrocatalytic activity is observed at pH lower than 11.5. Under voltammetric conditions the modified electrode exhibits a non-Nernsti an potential/pH shift (-88 +/- 3 mV per pH unit). A reasonable explana tion of the E/pH behavior in alkaline solution is given and an oxidati on mechanism of Co-II to Co-III is proposed in terms of hydrous cobalt oxides. No detrimental effects on the electrocatalytic oxidation of p olyhydric compounds are observed in the presence of high acetonitrile concentrations (up to 40%). Inspection by SEM of the cobalt-based depo sit evidenced the presence of grain-like microcrystallites on the glas sy carbon surface.