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

Abstract

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% C_spec 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.