Abstract
Recently, owing to increase in awareness of energy crisis, energy storage has become a new field as well as an important issue for energy saving. The supercapacitor has attracting great attention owing to its high power density, short charging time and safety during operation. However, the energy density of the supercapacitors is still lower than that of lithium-ion battery, as a result, restricting the application of supercapacitors. In this regards, enhancing energy density of the supercapacitors is the main theme of current research. In this work, graphene was synthesized and polystyrene (PS) spheres were used as templates to fabricated graphene-based porous electrodes for supercapacitors. The feature of the processing for porous graphene electrodes is that the thermal reduction method to reduce graphene oxide and to remove PS spheres can be completed simultaneously. Owing to the presence of porous structure in electrodes, it is expected that the electrodes possess higher specific surface area and specific capacitance. Regarding the use of PS spheres, we chose two sizes of PS spheres as templates and studied the influences of PS size and amount on the structure and capacity of the porous graphene electrodes. According to the results, the electrode containing 70 wt% PS spheres with a size of 0.2 μm possess a capacitance of 84.5 F/g. In order to enhance the electrical conductivity of the electrodes dopamine was added during the process and the electrodes were subsequently subjected to heat treatment at 800 ℃. As a result, nitrogen atoms were successful doped into porous graphene and formed nitrogen-doped porous graphene, which could effectively reduce two orders of magnitude in the sheet resistance and achieved a better capacitance of 168.8 F/g.