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 catalytic deposit was investigated by cyclic voltammetry and scanning electron microscopy (SEM). It is pointed out that, at relatively low coverage of cobalt, two main redox processes, Co-II --> Co-III and Co-III --> 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-Nernstian potential/pH shift (-88 +/- 3 mV per pH unit). A reasonable explanation of the E/pH behavior in alkaline solution is given and an oxidation mechanism of Co-II to Co-III is proposed in terms of hydrous cobalt oxides. No detrimental effects on the electrocatalytic oxidation of polyhydric compounds are observed in the presence of high acetonitrile concentrations (up to 40%). Inspection by SEM of the cobalt-based deposit evidenced the presence of grain-like microcrystallites on the glassy carbon surface.