Facile one-step synthesis of Co(OH)2 microsphere/graphene composites for an efficient supercapacitor electrode material

A simple one-step hydrothermal method is developed for the synthesis of Co(OH)(2)/graphene (Co(OH)(2)/GN) composites, during which graphite oxide was reduced and Co(OH)(2) particles were in situ formed on the GN sheets. The morphologies, structures and the electrochemical properties of the composites were investigated. The results show that flower-like Co(OH)(2) microspheres, self-assembled by the acicular particles, are enveloped by the wrinkled GN sheets to form the Co(OH)(2)/GN composites. The composite electrode exhibits the highest specific capacitance (C-spec) of 433 F g(-1) at a discharge current density of 0.1 A g(-1) in 6 M KOH, which is much higher than that of pure Co(OH) 2 (217 F g (-1)) and GN (187 F g (-1)), and shows excellent rate capability (the capacitance retains 90.3% at 10 A g (-1)) and a long cycle life along with 99% Cspec retained after continuous 1000 cycle tests at a current density of 1 A g (-1). The enhanced electrochemical performance is attributed to the synergistic effects of the good redox activity of the Co(OH) 2 particles combined with the high electronic conductivity of the GN sheets, which predicts the composite to be a highly promising candidate as an electrode material in energy conversion/storage systems.