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 (O2) 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 O2 reduction are evaluated with linear sweep voltammetry and current–time chronoamperometry. The results show that the catalytic activity decreases in the sequence: α-MnO2 nanowire > amorphous MnOx nanoparticle > β-MnO2 microprism, and α-MnO2 nanowire is more stable than amorphous MnOx nanoparticle. Thus, α-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 O2 to peroxide (HO2−), and further introduction of α-MnO2 nanowire catalyzes the disproportionation of HO2− produced effectively, which enables 4-electron reduction of O2 at low overpotential. In addition, the composite possesses good durability.

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