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

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. (c) 2013 Elsevier B.V. All rights reserved.