Preparation And Performances Study Of New Three Dimensional Graphene Materials

With the increasing environmental problems,supercapacitors,as a new type of energy storage equipment,has been welcomed.And graphene,as an ideal electrode material,has also been the focus of attention.However,in the absence of protective agents,the strong van der Waals and ?-? stacking interactions between the two-dimensional(2D)graphene sheets lead to agglomeration of the graphene,leading to a great loss of specific surface area,limiting its performance and application.In this stduy,we start from the shortcoming of graphene,and hope that self-assembly of two-dimensional(2D)graphene into three-dimensional(3D)macrostructures to solve the problem of agglomeration of the graphene.In this paper,graphene oxide(GO)was synthesized by a modified Hummers method,and then GO was reduced by chemical reduction method(chemical reducing agents).In the reduction process,3D porous network structure was prepared through the strong van der Waals and ?-? stacking interactions between graphene,which prevented its agglomerate successfully.The method is not only low reaction temperature,short time,simple operation;but also can realize the the reduction and heteroatom doping of GO simultaneously.At the same time,the prepared graphene hydrogels were used as electrode materials for supercapacitors,which benefited from the abundant porous architectures.In this work,the heteroatom-doped 3D porous graphene hydrogels were prepared sucessfully by the three different types of reducing agents of carbohydrates,tetrathiafulvalene(TTF)and thiourea dioxide,which TTF and thiourea dioxide were used as reducing and doping agents.1.3D porous network structure graphene hydrogels(FRGHs,GRGHs,SRGHs)which had small amount of nitrogen doping were prepared by using the carbohydrates(glucose,fructose and sucrose)as reducing agents in the presence of ammonia.The electrochemical performances,the source of nitrogen and its influences on the electrochemical performances were analyzed.The results show that,the nitrogen and oxygen functional groups can induce an extra pseudo-capacitance,improving the specific capacitance.The capacitance of FRGHs,GRGHs and SRGHs were 153.5,145.0 and 150.3 F g-1 at 0.3 A g-1,respectively.The capacitance retention rates were 61.4,61.5 and 46.9% at the current density of 20 A g-1;and the value were 97.1,96.6 and 92.8% after 4000 cycles at 1 A g-1.2.Graphene/TTF nanocomposite(SGHs)which had large amount of sulfur-doped wasprepared by using TTF as reducing agents to further study the influences of heteroatom doping on the electrochemical performances.The results show that,the doping content of sulfur for SGHs is up to 26.23%;the specific capacitance can reach up to 212.5 F g-1;and the retention rates of the specific capacitance still maintains at 98% after 4000 cycles.3.3D porous network structure graphene hydrogels(RGHs)were prepared by using thiourea dioxide as reducing agents.The different degree of reduction for GO and the controllability of nitrogen,sulfur doping were realized by controlling the dosage of reducing agents;and RGHs with different specific surface area and pore size distribution were prepared.The synergistic effect of nitrogen,sulfur doping and its influences of heteroatom doping on the electrochemical performances were studied.The reseaches show that the content of nitrogen and sulfur gradually increased while the oxygen content gradually decreased with the increase of the amount of reducing agents.The specific surface area of RGHs(RGHs-1,RGHs-2 and RGHs-5)were different becaused of the different degree of reduction for GO;but its specific surface area can reach up to 173 m2 g-1,189 m2 g-1 and 135 m2 g-1,respectively.The N,S and O content of RGHs-1,RGHs-2 and RGHs-5 were 4.10,4.96 and 6.43%;0.53,0.66 and 0.84%;16.91,10.43 and 9.70%;respectively.The specific capacitance of the RGHs electrodes are evaluated to be 258.6,167.3 and 198.3 F g-1 at 0.1 A g-1 for RGHs-1,RGHs-2 and RGHs-5,respectively.RGHs-1,RGHs-2 and RGHs-5 can still be maintained at specific capacitances of129.1,110.8 and 114.7 F g-1 at 10 A g-1.The retention rates are 49.9,66.2 and 57.8% for RGHs-1,RGHs-2 and RGHs-5,respectively;and the retention rates of RGHs-1 can reach up to 97.2% after 4000 cycles at 1 A g-1.