Electrochemical properties of α-Co(OH)2/graphene nano-flake thin film for use as a hybrid supercapacitor

Porous nano-flake-like alpha-Co(OH)(2) thin films were prepared by electro-deposition on graphene nanosheets (GNS) and functionalized f-GNS at 1.0 V. The functionality of hydrophilic functional groups was increased by acid treatment to enhance electrode wettability and improve the compatibility between the electrode and the electrolyte. Hydrophilic functional groups can act as anchoring sites for the precursors, enabling Co(OH)(2) to more grow easily on an f-GNS electrode. The density and thickness of the alpha-Co(OH)(2) deposition on the f-GNS electrode (13.1 mu m) was greater than that on the GNS (12.3 mu m) electrode. The specific discharge capacitance of the alpha-Co(OH)(2)/f-GNS electrode decreased from an initial value of 2,149mFcm(-2) to 1,944 mFcm(-2) over 1000 cycles, demonstrating the retention of 90% of its discharge capacitance. A hybrid capacitor was also assembled to evaluate the characteristics of a two-electrode system using alpha-Co(OH)(2)/f-GNS as the cathode. The power and energy densities of the Co(OH)(2)/f-GNS supercapacitor are 1,137Wkg(-1) and 43Whkg(-1) at 8mAcm(-2), respectively.