Mechanism of potentiostatic deposition of MnO 2 and electrochemical characteristics of the deposit in relation to carbohydrate oxidation

Abstract

Cyclic voltammetric (CV) and chronoamperometric (CA) studies on potentiostatic deposition of MnO 2 on Pt from Mn(II) solution in very weakly alkaline media show the process to be controlled by a one-electron transfer step, which means that the deposition proceeds through the generation of Mn(III). The electrocatalytic activity of the deposited electrode towards carbohydrate oxidation is found to be maximum at an optimum amount of deposition. Chronopotentiometric (CP) and CV measurements show that the oxidation of carbohydrates on the deposited electrodes follows a catalytic EC (electrochemical–chemical) mechanism via electrolytic formation of Mn(V) and its subsequent consumption either by disproportionation or by chemical reaction in the presence of carbohydrates. The rate constants of the reaction of Mn(V) with dextrose and fructose have been obtained from CA results. The relative order of the oxidation currents for dextrose and fructose as well as their dependence on carbohydrate concentration has been discussed. Replacement of Pt by carbon as the electrode support material does not affect the electrocatalytic activity of the MnO 2 deposit. The observed linear variation of the steady state oxidation currents with carbohydrate concentration can be exploited for analytical application.