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

Publisher Website
Google Scholar
Abstract
The catalytic function and activity of manganese oxides (MnOx: Mn2O3,Mn2O3, Mn3O4,Mn3O4, Mn5O8,Mn5O8, and MnOOH) to the electrochemical reduction of O2O2 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, ip,1ip,1 for a two-electron reduction of O2O2 to hydrogen peroxide (HO2−)(HO2−) and ip,2ip,2 for a two-electron reduction of HO2−HO2− to OH−.OH−. The peak current heights of ip,1ip,1 and ip,2ip,2 changed greatly depending on the kind of MnOx species incorporated into the MnOx/Nafion-modified gold electrodes; ip,1ip,1 increased and ip,2ip,2 decreased. On the assumption that HO2−HO2− produced in the first reduction step is chemically decomposed into O2O2 and OH−OH− with a catalytic action of MnOx and that this regenerated O2O2 is reduced again in the same first reduction step, we evaluated the catalytic activity of MnOx using the values of ip,1ip,1 and ip,2.ip,2. MnOOH provided the highest catalytic activity to the electrochemical reduction of O2.O2. This result was supported by another experiment by using a chemical method where catalytic decomposition of HO2−HO2− with MnOx was estimated by measuring the O2O2 concentration directly with a commercial oxygen sensor. © 2002 The Electrochemical Society. All rights reserved.