Electrochemical characterization of carbohydrate oxidation at copper electrodes

The electrochemical oxidation of carbohydrates at copper electrodes in alkaline solution is studied by cyclic voltammetric and rotating ring-disk electrode experiments. It is demonstrated herein that an important step in the oxidation of carbohydrates is their interaction with the oxide/hydroxide layer covering the electrode. This interaction is believed to involve the Cu(I) oxidation state although interaction with Cu(II) may also occur once it is formed. The extent of this interaction is measured by the decrease in peak height and electrochemical charge under the Cu(II) formation wave, and is sugar dependent. It is interesting that there is a correspondence between the extent of the interaction and the oxidative charge measured between 0.4 and 0.6 V (Ag/AgCl reference electrode) in the presence of carbohydrates. Structural effects may be influencing the interaction between carbohydrates and the electrode surface. The oxidation of many carbohydrates occurs in the potential region corresponding to the formation of Cu(III). Rotating ring disk electrode experiments strongly suggest that Cu(III) plays an important role in carbohydrate oxidation after the adsorption step. The electrooxidation of glucose at copper electrodes in alkaline solutions goes beyond the formation of gluconic acid (two electron transfer). Further oxidation may continue through CC bond cleavage. A mechanism for the oxidation of carbohydrates at copper electrodes is proposed. The mechanism includes the formation of complex species between the carbohydrates and the copper.