Electrochemical Characterization of Catalytic Activities of Manganese Oxides to Oxygen Reduction in Alkaline Aqueous Solution

The catalytic function and activity of manganese oxides (MnOx: and MnOOH) to the electrochemical reduction of in 0.10 M KOH aqueous solution have been investigated by cyclic voltammetry at MnOx/Nafion-modified gold electrodes. Two successive reduction current peaks were observed at Nafion-modified electrodes in the cyclic voltammograms, for a two-electron reduction of to hydrogen peroxide and for a two-electron reduction of to The peak current heights of and changed greatly depending on the kind of MnOx species incorporated into the MnOx/Nafion-modified gold electrodes; increased and decreased. On the assumption that produced in the first reduction step is chemically decomposed into and with a catalytic action of MnOx and that this regenerated is reduced again in the same first reduction step, we evaluated the catalytic activity of MnOx using the values of and MnOOH provided the highest catalytic activity to the electrochemical reduction of This result was supported by another experiment by using a chemical method where catalytic decomposition of with MnOx was estimated by measuring the concentration directly with a commercial oxygen sensor.