Preparation And Electrochemical Performance Of Reduced Graphene Oxide/Metal Hydroxides Composite Materials

Supercapacitors (SCs), known as electrochemical supercapacitors (ESCs) or ultracapacitors, are considered as promising candidates for energy storage due to their high-power performance, long cycles life, and low maintenance. However, its low energy density and high production costs restrict the development of supercapacitors. To overcome these disadvantages, one of the most effective way is to develop new electrode materials.First, we synthesized reduced graphene oxide/cobalt hydroxide (rGO/Co(OH)2) composite through a solvothermal process for supercapacitors. Then, rGO/nickel-cobalt layered double hydroxide (rGO/NiCo LDH) and rGO/NiCo LDH/Ni foam were prepared using a solvothermal method. The structure and morphology of these composites were characterized by field emission scanning electron microscopy, Raman, X-ray diffraction and thermogravimetric analysis. The electrochemical characteristics of the electrodes made of rGO/Co(OH)2 composite were tested by the cyclic voltammetry and galvanostatic measurements. The results are as follows:1. Co(OH)2 nanoparticles are uniformly grown on rGO surface. This composite exhibited a significantly enhanced specific capacitance which is superior to rGO and Co(OH)2, owing to the synergy between the rGO and Co(OH)2.2. Flower-shaped rGO/NiCo LDH composite exhibited a significantly enhanced specific capacitance of 2238 F g-1 at 1 A g-1. Moreover, the specific capacitance decreased by only 19% after 1000 cycles at 10 A g-1. There is synergy between graphene and NiCo LDH as well as the synergy between nickel and cobalt, so that the composite material has excellent electrochemical properties.3. We present a facile one-step method of in-situ growing NiCo LDH simultaneously with rGO on Ni foam through a solvothermal process for supercapacitors for the first time. The rGO/NiCo LDH/Ni foam composite exhibited a significantly enhanced specific capacitance of 3383 F g-1 at 1 A g-1 in a three-electrode system. The superior electrochemical performance is attributed to the hierarchical porous nanostructures. More importantly, this method could avoid the use of conductive agents and polymer binders, thus the electrical conductivity of this composite is superior.