| Supercapacitor is a new type equipment for electric energy storage, combines the advantages of both conventional capacitors and rechargeable batteries. Due to their high power density, long-lived cycle life and environment adaptable, supercapacitor has been emerging in power source applications such as consumer electronics, electric vehicles and defense equipment. Electrode material is a key factor of the supercapacitor and it determines the properties supercapacitor. Graphene, with its excellent properties including large surface area, high electrical conductivity and a broad electrochemical window, viewed as the new supercapacitor electrode material that has great analysis value. Manganese dioxide as representatives of metal oxide has a high Faradic pseudo-capacitance. Therefore, prepare the MnO2/graphene composites will improve the performance of supercapacitor to utilize the synergistic effect of individual material.In this study, graphene oxide(GO) is firstly fabricated from natural graphite via an improved method, graphene aerogel has been prepared by microwave digestion through reducing GO. The influence of reaction time on the morphology, structure and performance were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The results show that the optimal reaction time is 10 mins, graphene aerogel possess well-defined and interconnected 3D porous networks, which could contribute to the fast adsorption and diffusion of the ions the capability to form electric double-layer. The specific capacitance of graphene aerogel is 203.9 F·g-1 at a scan rate of 2 mV s"1 in 6 M KOH and the loss of specific capacitance was nearly neglectable after 1000 cycles, demonstrating its excellent long-term cycling stability.On this basis, graphene aerogel, as the substrate for loading ?-MnO2 by liquid deposition. The prepared nanosized ?-MnO2/graphene aerogels composites were characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), thermogravimetry analysis. The results showed that the surfaces of graphene aerogels are fixed with many MnO2 nanofibers, and take on a dandelion-like appearance. Besides, the composites loaded amount of ?-MnO2 were about 25%. The Electrochemical measurement showed that the specific capacitance of the composites are as high as 328.0 F·g-1 at a scan rate of 2 mV s-1, which was increased 60.9% than the graphene aerogel (203.9 F·g-1) by microwave digestion. The capacitance retention of nanosized ?-MnO2/graphene aerogels composites were above 90.3%, which exhibited excellent cycle performance.Currently, mostly the preparation of graphene with MnO2 composites use Multi-step reaction, therefore, GO as the substrate, MnO2/graphene aerogels composites were prepared via one-step hydrothermal routine with permanganate as manganese source and manganese sulfate as reductant. The structure and morphology of composites were studied by SEM, XRD and TG. The results showed that the surfaces of graphene aerogels are fixed with a certain amount of spherical particles, which are amorphous nano-structured manganese dioxide. The composites loaded amount of MnO2 were about 23.4%. The Electrochemical measurement showed that the specific capacitance of the composites are up to 258.9.0 F·g-1 at a scan rate of 2 mV s-1, which was increased 39.8% than the graphene aerogels (185.2 F·g-1) by traditional hydrothermal. Although the supercapacitor used amorphous nano-structured MnO2/graphene aerogels as active electrode material has an initial capacitance loss, the specific capacitance after 500 cycles stabilized nearly at a fixed value. |
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