Manganese oxide-graphene composite as an efficient catalyst for 4-electron reduction of oxygen in alkaline media

The catalytic activity of manganese oxide (MnOx)-graphene composite prepared by a physical method towards oxygen (O-2) reduction reaction in 0.1 M KOH solution has been investigated. For a better performance, MnOx materials with different crystallographic structures and morphologies have been synthesized, and their catalytic properties and stability for O-2 reduction are evaluated with linear sweep voltammetry and current-time chronoamperometry. The results show that the catalytic activity decreases in the sequence: alpha-MnO2 nanowire > amorphous MnOx nanoparticle > beta-MnO2 microprism, and alpha-MnO2 nanowire is more stable than amorphous MnOx nanoparticle. Thus, alpha-MnO2 nanowire is selected to combine with graphene. The modification of graphene on GC electrode leads to ca. 130 mV positive shift of the half-wave potential for the reduction of O-2 to peroxide (HO2-), and further introduction of alpha-MnO2 nanowire catalyzes the disproportionation of HO2- produced effectively, which enables 4-electron reduction of O-2 at low overpotential. In addition, the composite possesses good durability. (C) 2012 Published by Elsevier Ltd.