Synthesis And Application Of Novel Graphene-based N-doped Porous Carbon Composites As Supercapacitor Electrodes

Supercapacitors have attracted intense interest as ideal energy storage devices due to their high power capacity, long cycle life and cleanness. Carbon materials are considered to be the most attractive candidates as supercapacitor electrodes owing to their high electrical conductivity, large surface area and low cost. Various carbon materials including porous activated carbon,carbon nanotube, carbon fibers, porous carbon micro-nanospheres, and graphene have been demonstrated for high performance supercapacitors.We prepared N-doped hydrothermal carbon coated graphene composites (RGO@HTC) by carbonization of biomass glucose on the surface of GO under the help of ethylenediamine (EDA). In this one-step synthesis process, GO was used as conductive substrate and glucose acted ascarbon source. EDA not only doped the composites with nitrogen, but also induced hydrothermal carbonization of glucose to take place on the surface of GO sheets due to the electrostatic attractions between its amino terminal and negatively charged GO or glucose, leading to the formation of HTCs coated rGO. The obtained composites were further activated by KOH to enhance the porosity.The carbon composites materials possess ultra-high specific surface area (1749 m2·g-1) and pore volume (0.405 cm3·g-1). Depending on the good electrical conductivity of rGO substrate and the rich porosity of hydrothermal carbon surface, the RGO@HTC composites exhibited remarkable supercapacitor performances with a high specific capacitance (340 F·g-1 at the current density of 0.5 A·g-1), rate capacity and cycle stability. Moreover, the final composites had significantly increased masses, which could effectively offset the shortcoming of low productivity of rGO. The excellent supercapacitor performance and low-cost preparation of RGO@HTC composites would potentially pave the pathway for practical supercapacitor applications.Subsequently, we investigated the effects of carbon source and nitrogen source on the performance of hydrothermal caron coated graphene composites. When melamine was selected as nitrogen source and glucose as carbon source, the hydrothermal carbon coated graphene composites could be prepared successfully, and they possessed the high specific capacitance (336 F·g-1 at 0.5 A·g-1). The amount of melamine showed a great influence on the specific capacitance of these carbon composites, and the optimal amount of melamine was 1 g. When sucrose or starch was selected as carbon source and EDA as nitrogen source, amorphous carbonlayers could be also coated on the both sides of graphene oxide by hydrothermal reaction. Unfortunately, the specific capacitance was not attractive.