MnO 2 Nanofilms on Nitrogen-Doped Hollow Graphene Spheres as a High-Performance Electrocatalyst for Oxygen Reduction Reaction.

Platinum is commonly chosen as an electrocatalyst used for oxygen reduction reaction (ORR). In this study, we report an active catalyst composed of MnO2 nanofilms grown directly on nitrogen-doped hollow graphene spheres, which exhibits high activity toward ORR with positive onset potential (0.94 V vs RHE), large current density (5.2 mA cm-2 ), and perfect stability. Significantly, when it was used as catalyst for air electrode, a zinc-air battery exhibited a high power density (82 mW cm-2 ) and specific capacities (744 mA h g-1 ) comparable to that with Pt/C (20 wt %) as air cathode. The enhanced activity is ascribed to the synergistic interaction between MnO2 and the doped hollow carbon nanomaterials. This easy and cheap method paves a way of synthesizing high-performance electrocatalysts for ORR.