Preparation Of Graphene-based Electrode Materials For Electrochemical Capacitors And Characterization Of Their Electrochemical Performance

Graphene is named for a monolayer of carbon atoms with lots of sp2hybridization, which is tightly packed into a two-dimensional (2D) honeycomb crystal. The first physically experimental preparation of single-layer graphene accesses to varieties of amazing physics and chemistry properties. It exhibits outstanding characteristics of theoretical specific area, carrier mobility, mechanical and optical transport. Graphene, based on superior performance as above, has already revealed a large amount of potential applications on energy storge and conversion, catalysis, sensor and functional composite materials, etc. What is more, it is an ideal kind of electrode material for super-capacitor due to the high theoretical specific area and fast electron mobility. In this paper, on one hand, graphene and glucose-based activated carbon composites were developed because the agglomeration of chemically converted graphene resulted in the decrease of specific area; On the other hand, binder-free graphene paper was prepared owing to the addition of binder and conductive agent into the electrode materials powder. The morphology, structure, components and BET surface area of samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photo-electron spectroscopy (XPS) and nitrogen adsorption-desorption analysis. A two or three electrode system was employed to evaluate the electrochemical performance of the samples by cyclic voltammetry (CV), galvanostatic charge-discharge tests (GCD) and electrochemical impedance spectroscopy (EIS).The details are as follows:1) Glucose was dissolved with the continuous agitation in the different concentrations of graphene oxide ink. A series of samples were prepared by the same process of pre-carbonization, impregnation, activation, washing and drying. It was investigated that influence of the mass ratio of GO in the precursors was put on specific capacitance of samples. The results were as follows:it was optimized that3wt%GO was included in the precursor. The highest specific capacitance of334F g-1was achieved for the GAC/RGO composite prepared from the precursor with a GO mass ratio of3%(GR3), which exhibited a capacity retention of93.5%after1000cycles at a high current density of1000mA g-1. At the same time, it was revealed that the specific capacitance of GR3was higher than that of GAC and AGO. The precursor was based on the formation of hydrogen bonds between the hydroxyl groups in the glucose molecules and the oxygen-containing functional groups on the surface of GO.2) Large-scale graphene paper was synthesized by the reduction of graphite oxide paper(φ10cm) self-assembled at the liquid/air interfac with e hydrazine vapor form80wt%hydrazine hydrate solution. Furthermore, it was investigated for the influence of reduction and reduction temperature on the super-capacitive properties. The results were as follows:the graphene paper with the reduction temperature of150℃showed excellent capacitive behavior and long cycle life at the current density of1000mA g-1. The discharge capacitance for the material was142F g-1and the capacitance retention were99.8%after1000cycles in an aqueous electrolyte of6mol L-1KOH.