Preparation And Electrochemical Properties Of Graphene/polyaniline Composite Hollow Microsphere

With the development of the global economy,there is an increasing demand for the energy.The resource exhaustion and environmental contamination urgently require developing new reliable and sustainable energy storage and conversion technologies,such as lithium-ion batteries(LIBs)and supercapacitors.Electrode material is the key factor affecting the energy storage.Graphene has a great application prospect in the field of energy storage devices due to its unique performance,but the actual specific capacitance is lower than theoretical value.Polyaniline(PANI),one of the conducting polymers,has advantages of low cost and great capacitance for energy storage.Unfortunately,due to its swelling,cracks and shrinkage,PANI exhibits an inferior cycle life.The combination of PANI with graphene has been recognized as an effective way to improve the capacitance value and the cycling stability with synergistic effects.Besides,three-dimensional(3D)structure,especially hollow structured material can enhance the specific surface area and shorten diffusion length for both charge and mass transport.Therefore,the 3D graphene/PANI composite has a great application prospect as an electrode material.In this paper,Firstly,graphene carbon sphere(GCS)was synthesized by inverse suspension polymerization and pyrolysis.Subsequently,the GCS was treated by nitric acid to obtain the oxidized GCS spheres(OGCS)with negative charge on the surface.Then OGCS/PANI composites(GCS@PANI)were fabricated by electrostatic interactions and in situ polymerization of aniline on the OGCS.Finally,the GO was wrapped on the surface of GCS@PANI spheres by electrostatic self-assembly and reduction.Then the hierarchical graphene/PANI hollow microspheres(GCS@PANI@RGO)with sandwich structure were obtained.The morphologies and microstructures of the microspheres were characterized by scanning electron microscopy,X-ray diffraction,energy-dispersive X-ray spectroscopy,Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,thermogravimetric analysis and nitrogen adsorption measurements.The results show that the GCS@PANI-8 has a more regular crystalline and structure.The GCS@PANI@RGO composites demonstrate desirably hierarchical hollow microspheres with sandwich structure and the strong interactions such as electrostatic interactions,hydrogen bonding and ?-?interactions existed between the layers in hierarchical hollow microspheres.The diameter is about 20 ?m,and the wall thickness is about 4 ?m.The preparation process without etching templates can reduce the cost.The electrochemical behaviors of GCS@PANI@RGO as electrode were investigated by cyclic voltammograms(CV),galvanostatic charge-discharge(GCD)and electrochemical impedance spectroscopy(EIS).As the electrode materials of supercapacitors,the GCS@PANI-8@RGO showed a high specific capacitance of 446.19 F g-1 at the scanning rate of 5 mV s-1 in 1 M H2SO4 solution,and exhibit an outstanding long-term cycling stability with capacitance retentions of 93.4%after 1000 charging-discharging cycles at a current density of 2 A g-1 and even 88.7%after 5000 cycles.As the electrode materials of half cells,the initial capacities of the GCS@PANI-8@RGO was 1161.9 mA h g-1 and the capacity after 50th cycling was 495.0 mA h g-1.The sample of GCS@PANI-8@RGO also exhibited high-rate capability.The excellent electrochemical performance can be ascribed to the novel sandwiched hollow structure and the synergic effect of the three components of GCS,PANI and RGO.