Ni foam supported three-dimensional vertically aligned and networked layered CoO nanosheet/graphene hybrid array as a high-performance oxygen evolution electrode

•Vertically aligned and layered CoO nanosheet array was directly grown on Ni foam.•The nanoarchitecture can be controlled by changing the synthesis conditions.•Graphene was further conformally self-assembled on the nanosheet array.•The 3-D hybrid nanostructure can be directly used as an OER electrode.•This electrode showed remarkable catalytic activity and durability toward OER.

The sluggish oxygen evolution reaction (OER) represents a major kinetic bottleneck in water splitting. Herein we report the synthesis of a novel Ni foam (NF) supported 3-D vertically aligned and interconnected layered CoO nanosheet array with controlled density, layer thickness, and interlayer spacing, and the conformal self-assembly of graphene on this nanosheet array. The obtained CoO layered nanosheet/graphene hybrid nanoarray was directly used as an OER electrode, showing a current density of 10 mA cm−2 at an overpotential of 330 mV and a Tafel slope of 79 mV dec−1, both of which are much lower than pristine NF and the nanosheet array without graphene, and are among the lowest reported for Co-based OER catalysts and transition metal oxide-based ones measured under the same conditions. In addition, it can retain 92.4% of the current density after 66 h of chronoamperometry testing at a potential of 1.0 V vs. SCE, and 94.3% of the current density at 1.0 V vs. SCE after 200 cyclic voltammetry cycles (0–1.0 V vs. SCE). The excellent catalytic activity and stability toward OER are ascribed to the 3-D NF supported robustly grown networked layered nanosheet array structure and the synergistic effects between CoO layered nanosheets and graphene.

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