Electrocatalysis of both oxygen reduction and water oxidation using a cost-effective three-dimensional MnO2/graphene/carbon nanotube

Abstract

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 ∼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 show this hybrid to be a high-performance non-precious metal-based bi-catalyst for both the ORR and OER.