Further insights into the role of carbon in manganese oxide/carbon composites in the oxygen reduction reaction in alkaline media

Manganese oxides are known as active catalysts for the oxygen reduction reaction (ORR) in alkaline media. Being poor electronic conductors, for electrochemical applications, most of Mn oxides are either mixed with or supported on carbon materials, which impart electronic conductivity to the composite electrodes. A number of recent publications reported an immense influence of carbon materials on the electrocatalytic activity of transition metal oxides in the ORR. To better understand the role of carbon, in this work we utilize a wide variety of carbon materials and investigate the ORR on Mn2O3/carbon composites combining experiment with kinetic modeling. Such an approach allows us to discriminate the contribution of carbon in the ORR activity of composites, underscoring its positive role in improving the oxide utilization, and acting as the ORR co-catalyst, but also its negative role in competing for the adsorption of O2. By juxtaposing the electrocatalytic activity with the structural and morphological characteristics carbon materials, we propose some rules of thumb for choosing carbons necessary for creating efficient oxide/carbon ORR electrocatalysts.