Fabrication And Capacitive Characteristic Of Carbon Electrode Materials For Layered Architecture Supercapacitor

In the21century, with the rapid development of the global economy, thedepletion of fossil fuel, and increasing environment pollution, there is an urgent needfor clean, efficient, and sustainable sources of energy, as well as new technologiesassociated with energy conversion and storage. As a new type green-energy storagedevice, supercapacitors exhibit high-power density, rapid charge/discharge, excellentreversibility and cycle-ability, which bridge function for the power/energy gapbetween traditional dielectric capacitors and batteries/fuel cells. Currently,supercapacitors are widely used in consumer electronics, memory back-up systemsand industrial power and energy management. In the cases of being used inlow-emission hybrid electric vehicles and fuel cell vehicles, which is considered asone of the most extensive applications in the near future, supercapacitors are coupledwith primary high-energy batteries or fuel cells to serve as a temporary energy storagedevice with a high-power capability to store energies when braking. However, it can’tbe ignored that low capacitor performance restricts the development ofsupercapacitors. Hence, researchers focus on how to improve their electrochemicalperformance. In this work, we produce reduced graphene oxide for potential use as theelectrodes of electric double layer capacitors (EDLCs). Also, commercial activatedcarbons (ACs) are employed to investigate the capacitive character of the electrodesand the electrochemical performance of the EDLCs, in order to research and developcarbon materials used in supercapacitors with high power and high specificcapacitance. The main studies are as followed:We successfully synthesized a single layer reduced graphene oxide by theHummers method. The morphology and microstructure of samples were examined byX-ray diffraction (XRD), atomic force microscope (AFM), ultraviolet-visiblespectrophotometry (UV-vis). Electrochemical properties were characterized by cyclicvoltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostaticcharge/discharge. The supercapacitors were tested in6M KOH electrolyte thatexhibited an excellent electrical double-layer capacitance behavior and lower equivalent series resistance (ESR). A high specific capacitance of106.2F/g wasobtained at the current density of500mA/g. The energy density of the reducedgraphene oxide could reach3.7Wh/kg at a power density of435.5kW/kg. Meanwhile,the supercapacitor devices exhibited excellent long-cycle life without obviousdownward trend after5,000cycle tests.EDLCs were also produced by using commercial ACs for electrode materials,and the electrochemical performance of ACs has been investigated by CV, EIS andgalvanostatic charge/discharge. A high specific capacitance of207F/g was obtainedat the current density of250mA/g. The energy density of ACs could reach7.2Wh/kgat a power density of213.7kW/kg. The supercapaciors presented excellent long-termcycling stability without any decay after5,000charge/discharge process.By comparing with the electrochemical performance of the EDLCs, it could beconcluded that the commercial made by Xinjiang have the highest specificcapacitance among the others. As to the selection of aqueous electrolyte solution,supercapacitors consisted of ACs and6M KOH system presented the lowest ESR andthe highest specific capacitance. In addition, if the mass ratio of negative to positiveelectrode was1:1, the supercapacitors showed the best performance.