Formation of NiCo2O4 rods over Co3O4 nanosheets as efficient catalyst for Li-O2 batteries and water splitting

A 3D structured NiCo2O4@Co3O4 hybrid was prepared by a two-step hydrothermal approach and subsequently employed as a highly efficient catalyst in oxygen reduction reactions (ORRs)/oxygen evolution reactions (OERs) and from a Li-O-2 battery perspective. The Co-NC possesses interconnected NiCo2O4 nanorods grown over a Co3O4 nanosheet structure, which facilitates charge transfer and enhances the electrical conductivity. Moreover, the 3D structured hybrids are directly used as a cathode catalyst for the Li-O-2 system and displayed a maximum in-depth-specific discharge capacity of 4386 mA h g(-1). In addition, significantly improved and stable cycling performance up to 60 cycles is observed compared with Co3O4 nanosheets at the limited capacity range of 500 mA h g(-1). The excellent electrochemical performance of the NiCo2O4@Co3O4 hybrid is mainly associated with the oxygen-deficient 3D architecture providing more catalytic active sites and can accommodate more discharge products. Further, ORR/OER activities of NiCo2O4@Co3O4 hybrid in aqueous media are also evaluated in 0.1 M KOH solution using the rotating ring disk electrode technique. For instance, the OER activity of NiCo2O4@Co3O4 hybrid (apex current is 4.18 mA cm(-2)) is an approximately 2.25 times higher than that of commercial RuO2 catalyst (1.84 mA cm(-2)). Since the catalytic activity in aqueous and organic medium is not necessarily the same, but of NiCo2O4@Co3O4 hybrid exhibiting excellent ORR/OER characteristics in both cases is worth mentioning. (C) 2017 Elsevier Inc. All rights reserved.