Preparation Of Graphene Assemblies And Their Electrochemical Applications

Owing to its unique two-dimensional structure and excellent properties,graphene has shown enormous potential applications in various fields, such aselectronic devices, composite materials, catalysts and energy storage, et al.Assembling graphene into macroscopic assemblies with hierarchical structures, notonly offers various methods to adjust the morphology and structure of grapheneassemblies, but also can improve their properties and extend their applications. In thisdissertation, we focus on the preparation of graphene assemblies and theirelectrochemical applications. Several macroscopic graphene assemblies wereconstructed through proper assembly strategies with graphene oxide as buildingblocks, and their electrochemical performances in electrochromic devices andelectrochemical double layer capacitors were investigated.Graphene/PANI multilayer films have been successfully fabricated by thecombination of LBL assembly and chemical reduction of grapheme oxide withhydroiodic acid. In addition, the thickness, conductivity and transmittance of themultilayer film can be easily tuned by changing the alternate deposition steps.Integration of graphene increased the conductivity, electrochemical stability andimproved the mechanical flexibility of the multilayer films, allowing it to be apromising electrode materials for electrochromic devices even without using ITO asthe supporting electrodes. The electrochomic device based on (graphene/PANI)15filmshowed good electrochromic performances and improved electrochemical stability.High-performance self-assembled graphene hydrogels were fabricated byone-step chemical reduction of graphene oxide with sodium ascorbate. This method isenvironmentally friendly, fast, energy saving, simple and readily scalable to industriallevels. The self-assembled graphene hydrogel, consisting of well-defined andcross-linked three dimensional porous structure, not only was electrically conductive(3S/m) and mechanically strong (storage modulus,275kPa), but also exhibited ahigh specific capacitance (240F/g) when used as electrode materials in supercapacitor. Furthermore, a mechanism of forming the self-assembly graphenehydrogels was proposed based on the study on the reaction condition and gelationprocess.Three-dimensional interpenetrating graphene electrodes were prepared byone-step electrochemical reduction of graphene oxide from its aqueous suspension.The pore sizes of the network are in the range of several micrometers to larger thanten micrometers, and the pore walls are nearly vertical to the surface of currentcollector. Because the high conductivity of graphene and interpenetratingmicrostructure of electrodes were convenient for electron/ion transportations, theinterpenetrating graphene electrodes based DLCs showed ultrahigh-rate capabilityand high specific capacitance. It was capable of replacing AEC for ac line-filtering.