Standing and Lying Ni(OH)₂ Nanosheets on Multilayer Graphene for High-Performance Supercapacitors

For conventional synthesis of Ni(OH)₂/graphene hybrids, oxygen-containing functional groups should be firstly introduced on graphene to serve as active sites for the anchoring of Ni(OH)₂. In this work, a method for growing Ni(OH)₂ nanosheets on multilayer graphene (MLG) with molecular connection is developed which does not need any pre-activation treatments. Moreover, Ni(OH)₂ nanosheets can be controlled to stand or lie on the surface of MLG. The prepared hybrids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The growth processes are suggested according to their morphologies at different growth stages. The enhanced electrochemical performances as supercapacitor electrode materials were confirmed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. Ni(OH)₂ nanosheets standing and lying on MLG show specific capacities of 204.4 mAh g^-1 and 131.7 mAh g^-1, respectively, at 1 A g^-1 based on the total mass of the hybrids and 81.5% and 92.8% capacity retention at a high current density of 10 A g^-1, respectively. Hybrid supercapacitors with as-prepared hybrids as cathodes and activated carbon as anode were fabricated and tested.