▎ 摘　　要

The electrochemical oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are of great interest since they are involved in energy conversion between fuel and electricity. Here, we developed a bifunctional MnO2/graphene/carbon nanotube that is free of noble metals and that could be a promising candidate electrocatalyst for these oxygen reduction and evolution reactions. It was shown to be able to act as an efficient cathode catalyst for the ORR, having a positive half-wave potential that differs by only similar to 55 mV from that of commercial Pt/C, and a high cathodic current density that is comparable to that of the Pt/C catalyst. Moreover, the hybrid exhibited superior durability with nearly no decay in ORR activity even after 10 000 s of continuous operation in 0.1 M KOH, while Pt/C shows a 20% decrease in the activity. Most importantly, the hybrid was also shown to be highly active for the OER. These observations showthis hybrid to be a high-performance non-preciousmetal-based bi-catalyst for both the ORR and OER.