Electrodeposited MnO2 as electrocatalyst for carbohydrate oxidation

The electrochemical oxidation of dextrose, fructose and sorbitol under galvanostatic conditions was carried out using both anodically and cathodically deposited MnO2 layers on platinum and carbon. The coated electrodes showed better electrocatalytic activity for the oxidation of carbohydrates than the bare substrates. Catalytic participation of some higher valent states of manganese in electron transfer relay is speculated, which finds support in the chronopotentiogram and the observed pH-dependence of the electrochemical parameters. The current potential plots showed Tafel behaviour for the MnO2/Pt electrode. The Tafel slopes were found to be relatively high, indicating kinetic complications. The observed unusual negative values of electrochemical reaction order on MnO2/Pt electrode were accounted for by considering slow desorption of oxidation products from the electrode surface. The adsorption isotherms of dextrose and fructose on MnO2 were determined. The current efficiencies of oxidation of carbonyl and hydroxyl groups were found to be similar to 40 and similar to 50% respectively. SEM pictures showed the cathodically deposited MnO2 on carbon to be more fine-grained and smoother than the corresponding anodic deposits.