Functionalizated Graphene With Organic Molecules And Its Enhanced Capacitance Performance

As a new energy storage devices, supercapacitors attract intensive attention because of their unique advantages including long cycle life, high power density. Electrode is one of important components in supercapacitors, while the electrode consists of corresponding materials. This implies that the performance of supercapacitors depend significantly on the electrode material. Therefore, to fabricate electrode material with the excellent performance is essential for the further developments in supercapacitors. In recent years, graphene has been being considered as a promising electrode material in applications of supercapacitors due to its large specific surface area, superior electrical conductivity and excellent chemical stability. However, in practical processes, graphene sheets usually suffer from agglomeration or restacking owing to the Vander Waals interactions between graphene sheets, which leads to a lower specific capacitance than as expected. Hence, to improve capacitive performance of graphene, some researchers are trying to introduce organic structures into graphene systems.In this thesis, we select the graphene as the matrix material and prepare the graphene-based composites using the non-covalent functionalization method. Through this method, the small organic molecules were attached on the surface of the graphene to form graphene-based composites. On the one hand, we characterized morphology and structure of each simple in details. On the other hand, we measured and evaluated the capacitative performance of the resultant materials systematically. The main contents are summarized as follows:The RGO/BPA composites with excellent electrochemical performance were prepared via noncovalent functionalization method. In the composite, BPA was adsorbed on the basal plane of RGO by π-π stacking interactions without disruption of graphene lattice. In this case, RGO can release electric double layer capacitance and BPA contributes pseudocapacitance to the overall capacitance through fast quinone/phenol redox reactions. Electrochemical tests show that the RGO/BPA composites exhibit ultrahigh specific capacitance of 466 F·g-1 at a current density of 1A·g-1, the excellent rate capability(more than 81% retention at 10 A·g-1 relative to 1 A·g-1) and superior cycling stability(90% capacitance decay after 4000 cycles). Consequently, the RGO/BPA nanocomposites can be regarded as promising electrode materials for supercapacitor applications.The RGO/1-naphthol composites were synthesized by noncovalent functionalization method. At a current density of 1 A·g-1, the RGO/1-naphthol electrode revealed an high specific capacitance of 370 F·g-1, which is much larger than that of the pure RGO(121F·g-1). In addition, 1-naphthol/RGO showed an excellent rate capability(more than 81% retention at 10 A·g-1 relative to 1A·g-1) and long cycle life(no capacitance decay after 5000 cycles). The excellent electrochemical performance for 1-naphthol/RGO electrodes is attributed to positive synergistic effect between 1- naphthol and RGO.3. Functionalized graphene hydrogels were prepared by solvothermal method. BPA was adsorbed on the basal plane of three-dimensional network the graphene with high surface area by π-π stacking interactions. The unique three-dimensional network structure of graphene hydrogels is beneficial to accelerate charge transfer between graphene and BPA and promote adsorption/intercalation of ions from the electrolyte to the composite. The prepared composites exhibited excellent electrochemical performance in term of high specific capacitance(404 F·g-1 at a current density of 1 A·g-1) and excellent cycle stability. These results demonstrate that the electrochemical properties of graphene-base materials can be improved through surface functionalization of the graphene and adjustment of graphene porous structure.