Design, Preparation And Performance Of Supercapacitors For Graphene Films And Modified Graphene

Supercapacitor as a new kind of environmental-friendly energy storage device, because of its high efficiency and non-polluting characteristics, has attracted more and more attentions in the view of"low carbon"economy. The electrode material is the key factor for supercapacitor. The rising graphene, a two-dimensional carbon material with one atomic thickness, is a type of ideal electrode materials for supercapacitor because of its large surface area, excellent conductivity, high mechanical strength and so on. Graphene oxide (GO) prepared by chemical method owns good film-formation property, which could be used to prepare"graphene paper"for application to free-standing electrode. In addition, metal nanoparticles could be facilely anchored onto GO sheets by the linkage of oxygen containing groups on the sheets, hereby forming graphene based composites. In the thesis, the research focuses on the preparation of graphene films, the graphene modification and their electrochemical capacitor properties. We have developed solution-casting method to prepare graphene/carbon nanotube (CNT) composite film, propose a hydrothermal route to fabricate graphene based composite films and investigate the capacitor performance of the as-prepared materials. The main contents are summarized as follows:1. GO, GO/CNT films were prepared by solution-casting method, which were further thermally annealed at 200℃to obtain the corresponding hybrid graphene, graphene/CNT films. The graphene/CNT films own high stability in electrolyte solution because the films are formed mainly by the interlayer interaction, i.e.π-πstacking and van der Waals force of graphenes. Compared with pure graphene film, the graphene/CNT films have better mechanical properties and higher electrical conductivity due to the contribution of CNTs. The graphene/CNT films have the specific capacitances of 70¹10 F/g and demonstrated pseudocapacitive behavior due to partial oxygen-containing groups remained on the electrode after thermal annealing, indicating potential in supercapacitor.2. GO/CNT films were prepared by filtration, which were reduced by water and realized self-assembly under the hydrothermal condition. Network structures withπ-πstacking were formed in the film. The hybrid films have good mechanical and electrical properties as well as good electrochemical capacitance performance, whose specific capacitance is about 180 F/g. This provided a facile and efficient route to prepare free-standing graphene based films. 3. Ni²⁺ ions were supported onto GO sheets by the interaction of metal ions and oxygen containing groups on the GO sheets, which were further reduced by hydrazine and heat treatment to prepare Ni nanopartilce/graphene composite. Graphene decorated by Ni nanopartilce have demonstrated higher electrical storage property than the pristine one.4. Carbon microtubes (CMTs) with the outer and inner diameter of 4⁸ and 3⁷μm were obtained by the carbonization of poplar catkins. The so obtained CMTs showed good performance, even better than CNTs in the test of supercapacitor. These results not only realize the resource recycling of poplar catkins and supplement novel building block for electrodes, but also provide material basis for deeply understanding the relationship between capacitor performance and pore structure in tubular carbon.