Air cathode of zinc-air batteries: a highly efficient and durable aerogel catalyst for oxygen reductionElectronic supplementary information (ESI) available. See DOI: 10.1039/c8nr07386d

In this communication, N-doped carbon shell encapsulated Co 3 O 4 @Co nanoparticles (NPs) were assembled on N-doped reduced graphene oxide to form non-precious metal aerogels (Co 3 O 4 @Co/N-r-GO) for oxygen reduction. In an alkaline medium, the aerogels exhibit comparable oxygen reduction reaction (ORR) performances to the commercial Pt/C with respect to half-wave potential, current density and durability. Zn-air batteries (ZABs) assembled with Co 3 O 4 @Co/N-r-GO as the air cathode display high average voltages of ∼1.38 and ∼1.3 V at a current density of 1 and 5 mA cm −2 , respectively, and show a specific capacity of ∼800 mA h g −1 . These results demonstrate that Co 3 O 4 @Co/N-r-GO materials are highly active and durable ORR catalysts for ZABs. The unique structure of the composite aerogel, i.e. the carbon shell encapsulated Co 3 O 4 @Co NPs and the 3D interconnected macroporous N-r-GO matrix, is responsible for its high ORR activity and stability. Encapsulated Co 3 O 4 @Co nanoparticles assembled on N-doped r-GO aerogels with high ORR and ZAB performances are synthesized via a biomass conversion strategy.