Synthesis of Co(OH)2/graphene/Ni foam nano-electrodes with excellent pseudocapacitive behavior and high cycling stability for supercapacitors

Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO₃)₂ aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)₂ has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg⁻¹ at current density of 2 and 32 Ag⁻¹, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag⁻¹, which is higher than that of Co(OH)₂/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)₂ and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes.