Construction And Supercapactive Behaviors Of Reduced Graphene Oxide/Electrochemucally Active Organic Composite Systems

Supercapacitor is a new type of energy storage devices, which combine theadvantages of both conventional capacitors that can deliver high power within a verysmall period and conventional rechargeable batteries that have high energy densities.Electrodes are essential conponents of supercapacitors, and furthermore electrode iscomposed of the electrode materials. Therefore, the research and preparation ofelectrode materials with good electrochemical performance are very important fordeveloping supercapacitors.In the present work, we select reduced graphene oxide （RGO） as a substrate toprepare RGO-based electrode materials with high performance for supercapacitor bymeans of a non-covalent modification or making composites. In addition, theelectrochemical capacitive behaviors of nickel-bismuth oxide composite are explored.The main is as follows:1. Anthraquinone （AQ） with electrochemically reversible redox couples（anthraquinone/anthracenol） is selected to decorate reduced graphene oxide （RGO）through a non-covalent modification. The π-π stacking interactions betweencomponents induce a favorable molecule orientation that the aromatic ring of AQ isparallel to the sp2network of RGO. Under this structure model, the fast redoxreactions between anthraquinone and anthracenol can occur at very low overpotentialsdue to a short distance between conductive substrate and electrochemically activesites. Thus, anthraquinone-decorated reduced graphene oxide （AQ-decorated RGO）effectively superimposes pseudocapacitance contributed by fast Faraday reactions ofAQ on electrical double layer capacitance rising from RGO nanosheets, whichenhances the overall capacitance of materials. Electrochemical measurements showedthat AQ-decorated RGO achieved a specific capacitance of236F g^-1within thepotential window of1.2V with high rate capability and long cycle life, which is muchlarger than that of a pure RGO (182F g^-1). It is more important issue that when thespecific current increases to10A g^-1, AQ-decorated RGO retains its specific energyup to68.5%of initial value (47Wh kg^-1) while its specific power increases20times more than that (300W kg^-1) at0.5A g^-1.2. Anthraquinone/reduced graphene oxide （AQ/RGO） is prepared in the waterphase systems. The components of products are analyzed by FT-IR and the structureand morphology are characterized using X-ray diffraction （XRD）, field emissionscanning electron microscopy （FESEM） and transmission electron microscope （TEM）,respectively. Electrochemical measurements show that there is a synergetic effect inthe resulting AQ/RGO, which an additional pseudo-capacitance contributed by thefast redox reactions of AQ is superimposed on the electrical double-layer capacitancearising from RGO. AQ/RGO can obtain a maximum value of312F g^–1at1A g^-1 andprovide a40%enhancement in specific capacitance compared with pure RGO.Meanwhile, AQ/RGO electrode has cellent rate capability. When specific currentincreases from1A g^-1 to50A g^-1（or by49time）, AQ/RGO still retains the specificcapacitance at59.3%of initial value at1A g^-1. Furthermore, after5000cycles, thecapacitance of AQ/RGO remains99.4%of the initial value, indicating excellentstability over the entire number of cycles.3. A nickel-bismuth oxide composite was firstly synthesized by thermallytreating the bismuth-nickel hydroxide mixture precursor, which was obtained throughsimultaneous solvothermal hydrolyzation of nickel and bismuth salt in N,N-dimethylformamide （DMF） at180°C. The structure and morphology of the composites werecharacterized using powder X ray diffraction （XRD） and field emission scanningelectron microscopy （FESEM）. The electrochemical behaviors were measured bycyclic voltammogram （CV）, galvanostatic charge discharge and electrochemicalimpedance spectroscopy. The results show that the molar ratio in nickel-bismuthoxide composite is a key factor to achieve excellent capacitance performance. Theoptimal ratio of the composite is given by means of the parallel experiments.Furthermore, the power density and energy density were discussed in detail when theresulting nickel-bismuth oxide composite was used as single electrode forsupercapacitors.