Study Of The Novel Structure And Capacitor Devices Based On Graphene Nano-materials

As a two-dimensional nano-material, Graphene possesses superior physical and chemical properties to other carbon materials, which have attracted great attentions since it was found. Due to the large specific surface area and unique electrical properties, graphene is a promising material in in the fields of energy conversion and storage. In this thesis, the new assembly structure of graphene can be achieved through the tuning the dimensions of graphene. The obtained functional graphene-based composites were characterized, and the applications for graphene composites in the supercapacitor devices are presented. Main works are as follows:(1) A novel core-sheath hierarchical MnO2 modified graphene fiber has been fabricated and then applied into all-solid-state supercapacitor. Firstly, the graphene fiber(GF) with high strength, high electrical conductivity and mechanical flexibility was prepared by hydrothermal treatment, then three-dimensional(3D) graphene networks assembled on GF(G/GF) via electrochemical stratiges,following the MnO2 nanostructures deposited on the 3D graphene network surrounding graphene fiber. Finally, the core-sheath hierarchical GF-G-MnO2 was fabricated and then used as electrodes in the all-solid-state flexible fiber supercapacitor with the polymer as electrolyte. Such material shows high electrochemical capacitance, good stability and enhanced electrochemical capacitive behaviors with robust tolerance to mechanical deformation, indicating a promising for being woven into a textile for wearable electronics.(2) Taking into account the unique characteristics for various structures of graphene, we successfully prepared 3D graphene quantum dots(GQDs)/graphene composites which exhibit large specific surface area and high capacitor performance. The GQD and 3D graphene were first fabricated by electrochemical method and hydrothermal synthesis, respectively. Then, 3D graphene quantum dots(GQDs)/graphene composites were obtained via electrochemical method with GQDs as electrolyte, which showed a high specific capacitance, representing a more than 90% improvement over that of the supercapacitor made from pure 3DG electrodes.(3) Graphitic carbon nitride(g-C3N4) shows a similar planar structure with graphene, which can assemble onto graphene basal plan through ?-? electronic conjugation. Consequently, we designed and fabricated the 3D g-C3N4 functionalized graphene composites(g-C3N4@G) using a simple one-step hydrothermal treatment. The prepared composites with a high nitrogen content of 11.44 at% can increase the pseudocapacitance effectively. Besides, the introduction of g-C3N4 into the composites can efficiently reduce the aggregation of graphene during the hydrothermal proccess, leading to a higher available electrochemically active surface area for increasing EDLC energy storage.(4)The 3DG with high interconnected network pore structure and specific surface area has drawn wide attention in the area of capacitor application. It is nessesry to construct the micropore structures in the 3D macro-network for graphene(the mean size of pores is 10 ?m) to improve the surface area and further increase the capacitance. According to this, we proposed that introducing small size graphene sheets into the graphene macro-network to increase the specific surface area. Firstly, the small graphene sheets with the size of less than 1?m were produced using ultrasonic cell crusher, then, the hierarchical pore structure for 3D graphene materials were successfully prepared via electrochemical method. The obtained materials showed an improved performance for the EDLCs.