Preparation And Electrochemical Properties Of Cobalt-based Graphene Composites

Cobalt-based graphene composites have a wide range of applications in the fields of energy storage and conversion, such as lithium ion batteries, supercapacitors, fuel cells, electrolysis of water. Since cobalt-based graphene composites exhibit preferable electrochemical performance and are relatively inexpensive, they are regarded as one of the most promising materials to substitude noble metal in some applications. The purpose of this paper is to prepare novle structured cobalt-based graphene composites to meet the needs of efficient oxygen evolution reaction and high performance supercapacitor by a green and efficient electrodeposition method.Firstly, CoS@eRG (electrochemically reduced graphene) electrodes were successfully prepared by using a two-step electrodeposition method. The thin film of CoS@eRG with thickness of 1 μm was composed of graphene and CoS nanosheets, which were nicely integrated together with open channels. The CoS@eRG composites exhibit an impressive specific capacitance of 3386 F/g at a current density of 1 A/g,2.6 times that of the CoS electrode. A CoS@eRG Ⅱ activated carbon asymmetric capacitor exhibits maximum energy density of 29 Wh/kg and power density of 40 kW/kg. Furthermore,70% capacitance retention is obtained after 10000 cycles at a current density of 1 A/g.Secondly, NixCo2XOH6X@eRG electrodes were prepared by a two-step electrodeposition method. The thickness of nickel-cobalt hydroxide nanosheets is about 10-20 nm. The graphene sheets and nicke-cobalt hydroxide nanosheets closely anchored together. The Tafel slope of NixCo2XOH6x@eRG electrode is 67 mV/dec, which is 15.2% lower than that of NixCo2xOH6X electrode. The overpotential of NixCo2XOH6X@eRG electrode is only 280 mV at a current density of 10 mA/cm2, which is 12.5% lower than that of NixCo2XOH6X electrode.Finally, NiCo2O4@eRG electrodes were prepared by electrodeposition and calcination method. The NiCo2CO4@eRG composites exhibit a specific capacitance of 1076 F/g at a current density of 1 A/g,1.9 times that of the NiCo2CO4 electrode. NiCo2O4@eRG electrodes exhibit high rate capability. When the current density raises to 20 A/g, the specific capacitance of NiCo2CO4@eRG electrodes can still remain 80.2%, while only 62.7% capacitance retention is achieved by NiCo2CO4 electrodes.84% capacitance retention is obtained for NiCo2O4@eRG electrode after 1000 cycles at a high current density of 10 A/g, showcasing its high cycling stability.