Oxygen reduction reaction on nanosized manganese oxide particles dispersed on carbon in alkaline solutions

In this work a manganese oxide dispersed on a high surface area carbon powder at two ratios (MnyOx/C) was evaluated as catalyst for the oxygen reduction reaction (ORR) in alkaline solutions. An impregnation method was used to prepare the catalysts, starting from a manganese nitrate precursor solution containing the carbon powder (Vulcan XC-72). A thin porous coating rotating disk electrode was employed to collect the experimental ORR polarization data and the results obtained were analyzed with the application of the flooded-agglomerate/thin film model for the catalyst layer. Results indicated that the reaction is sensitive to the manganese oxide to carbon ratio on the catalyst. The catalyst containing lower MnyOx/C ratio tended to follow the peroxide pathway (2e(-) mechanism) forming peroxide ions. When the MnyOx content is increased the complete reduction of oxygen to hydroxide ions pathway (the 4e(-) mechanism) takes place into some extent at low potentials due to the occurrence of a catalytic disproportionation of HO2-. (c) 2005 Elsevier B.V. All rights reserved.