Supercapacitors Based On Graphene And Its Composite Materials

The problems of energy and environment caused by the shortage of fossil fuels and global warming have been growing recently. As a result, it is an irreversible trend to vigorously develop clean and renewable energy. As a new storage system between traditional capacitor and lithium ion battery, supercapacitor which could provide high power density has a long service life and stability. Graphene, a single atomic layer which is constituted by a carbon atom with the type of sp2 hybrid orbitals consisted of hexagonal honeycomb lattice shaped, known as an unique two-dimensional conjugate structure gives its excellent electrical conductivity, mechanical properties,electrochemical stability and large theoretical specific surface area make it an ideal of super capacitor electrode material. This dissertation used the modified hummers method to prepare the precursor of graphene—Graphene Oxide(GO) as the substrate electrode material, then hydrothermal method had been adopted to reduce GO in order to obtain a porous three dimensional graphene films(r GO Films), while we also prepared Graphene/Poly(3,4-ethylenedioxythiophene) composite according the coating method, their chemical compositions, morphologies and electrochemical performances were characterized. The main results are summarized as follows.(1) Aqueous GO dispersion was mixed with a little aqueous HCl solution, followed by vigorous stirring for several minutes using a vortex mixer to give GO hydrogel, then prepared by cast drying the resultant hydrogels at ambient condition. The as-prepared GO films were submitted to a Teflon-lined autoclave and hydrothermally treated at 180 o C for 24 h. Finally, a porous three dimensional graphene films couuld be achieved after mechanical pressure. The resultant r GO films exhibit a good gravimetric specificcapacitance of 218 F·g?1and excellent capacitance performances with high volumetric capacitance of 244 F·cm?3(1 A· g?1) as well as superior rate capability(82.5% retention at 20 A ·g?1) and excellent cycling stability as confirmed by retaining 92% of its initial capacitance even after 10000 cycles of charging/discharging.(2) Aqueous GO dispersion(10.4 mg·m L? 1) was mixed with an aqueous PEDOT/PSS(13 mg·m L? 1) dispersion, an uniformly mixed gel was obtained followed by vigorous stirring for several minutes using a vortex mixer after adding a little protonic acid. Then the as-prepared mixed gel was coated on the glass substrate for 5h,followed by treated with concentrated sulfuric acid to remove PSS. Finally, the Graphene/PEDOT composite films were obtained after reduced by HI. As the result,Graphene/PEDOT composite films exhibit high specific capacity and excellent rate capability when GO has quality ratio of 3:1 with PEDOT/PSS. In addition, there have a great influence on the electrochemical properties of compound films according to change reduction time.