Morphology controlled high performance supercapacitor behaviour of the Ni–Co binary hydroxide system

•Ni–Co binary hydroxide systems with controllable morphologies were fabricated.•Different morphologies lead to distinct supercapacitive behaviours.•The performance degradation at high mass loadings can be greatly mitigated.•Asymmetric cells composed of hydroxides and graphene showed excellent performance.

The morphology evolution of the Ni–Co binary hydroxides was studied varying from nanosheets, to nanoplate–nanospheres, to nanorods and to a nanoparticle geometry by simply controlling the Co:Ni ratio in the initial reactant. High capacitances of 1030 F g−1 and 804 F g−1 can be achieved in the 1-D nanorod morphology at mass loading of 1 mg cm−2 and 2.8 mg cm−2 at a current density of 3 A g−1, respectively. To demonstrate its practical application, the binary hydroxide electrode was coupled with chemically-reduced graphene (CG) forming an asymmetric supercapacitor in order to improve the potential window and thus energy density. The asymmetric supercapacitor delivers a high energy density of 26.3 Wh kg−1 at the power density of 320 W kg−1. The approach of controlling morphology and crystallinity of the binary system for optimizing supercapacitive performance may be applied developing other promising multiply metal hydroxide/oxide systems for supercapacitor applications.

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