Synthesis Of Graphene And Conductive Polymer Composites And Their Application In Supercapacitors

As the development of economy and science and technology,the increasing demand for energy occurs.Currently,the main source of energy is the burning of fossil fuels and small amounts of wind,nuclear and geothermal energies are used.However,traditional fossil fules are non-renewable and being exhausted fast due to the wanton destruction in recent years.At the same time,due to the emission of a large amount of polluted gas originated from the delpetion of fossil fuels,they have emerged a harmful impact on the environment and human health.Therefore,the exploition of a clean and renewable energy source has been a foucs of the world.Supercapacitors as electrochemical energy store and convertion devices have attracted considerable attentions due to their advantages of high power density,excellent cycle stability,fast charge/discharge performance,zero pollution discharge and wider working voltage.Generally,according to different energy storage mechanism of electrode materials,supercapacitors can be divided basically into electrical double layer capacitors?EDLC?and faradaic pseudocapacitors.In the former type,capacitance of EDLCs results mainly from the accumulation of charges at the electrolyte/electrode interface,which representative materials are carbon materials,such as activited carbon,mesoporous carbon and graphene.In the latter type,namely Faraday capacitors,the pseudocapacitance is produced through fast and reversible redox charge transfer of electrochemical active electrode materials at the electrolyte/electrode interface,which representative materials are metal oxide/hydroxide,conductive polymer,e.g.,CoO,Ni?OH?₂,polyaniline and polypyrrole.Owning to carbon materials possess good cycle stability but have low specific capacitance,while pseudocapacitive materials show high specific capacitance but have poor cycle stability.Thus,many efforts have performed to combine with carbon materials and pseudocapacitive materials with complementay advantages.Due to the synergistic effect of the both materials,the electrochemical performances of supercapacitors would further be improved.This thesis mainly reported the prepared process of reduced graphene oxide,which possessed high conductivity,excellent thermal stability and large speific area,its application in preparation of binary or ternary composites with conductive polymer,metal hydroxide and nickel-cobalt sulfide by means of electrochemical or chemical methods.The obtained composites can be used as supercapacitor electrode materials,which show good electrochemical performances.The main contents are as follows:1.Preparation of reduced graphene oxide/poly?azure C??rGO/PAC?composite via one step cyclic voltammetry?CV?.Scanning electron microscope?SEM?,Fourier transform infrared spectrometer?FTIR?,Raman spectroscopy?Raman?and X-ray photoelectron spectroscopy?XPS?were carried out to characterize the morphology and structural traits of the composite.The electrochemical performances of the composite were investigated by CV,galvanostatic charge-discharge?GCD?and electrochemical impedance spectroscopy?EIS?.The preparaed rGO/PAC composite exhibits higher electrochemical performances compared with graphene/poly?azure C??GO/PAC?,poly?azure C??PAC?and reduced graphene oxide?rGO?.the rGO/PAC composite shows high specific capacitances of 500 F/g at 0.5 A/g and 400 F/g at 10A/g.Moreover,at 0.5 A/g,the rGO/PAC composite has a specific capacitance rentention of 93%after 1000 cycles.2.Reduced graphene oxide/poly?azureC?/Ni?OH?₂ ternary nanocomposite was fabricated by a two-step method.First,synthesis of graphene oxide/poly?azure C??GO/PAC?composite was conducted via in-situ chemical polymerization.Then,the obtained GO/PAC composite was dispersed and Ni?NO₃?₂·6H₂O was dropped into with different mass ratio?mass ratio:Ni?NO₃?₂·6H₂O:GO/PAC=10:1,20:,30:1 and60:1?.Graphene/poly?azureC?/Ni?OH?₂-X?X=10,20,30,and 60?ternary nanocomposites with the above corresponding different mass ratios were obtained by a hydrothermal process.SEM,X-ray diffraction?XRD?,FTIR,Raman and XPS were adopted to characterize the surface morphology and structural properties of the ternary nanocomposite.The electrochemical performances of the composite were systematically investigated by CV,GCD and EIS.The results show that the electrochemical performance of graphene/poly?azureC?/Ni?OH?₂-20 is better than those of the other three composites.At a current density of 1 A/g,the reduced graphene oxide/poly?azure C?/Ni?OH?₂-20 ternary nanocomposite shows high specific capacitance of 1490 F/g.Besides that,the cyclic rentention of the ternary nanocomposite was 100%after charging-discharging test for 1000 cycles at a current density of 5 A/g,which proved that the graphene/poly?azure C?/Ni?OH?₂-20 ternary nanocomposite has high structural stability and potential as an electrode material for supercapacitors.3.Reducedgrapheneoxide/nickel-cobaltsuflide/poly?azureC??rGO/NiCo₂S₄/PAC?ternary composite was prepared by a two-step method:hydrothermal process and electrochemical deposition.First,graphene/nickel-cobalt sulfide?rGO/NiCo₂S₄?was directly loaded on the nickel foam by a two-step hydrothermal synthesis.Then,poly?azure C?was electrodeposited by potentiostatic method on the surface of rGO/NiCo₂S₄ nickel foam.The resulting rGO/NiCo₂S₄/PAC-X?X=2,4,5 and 6 min?ternary composites were obtained with different electrodeposition time.SEM,XRD,FTIR,Raman and XPS were conducted to characterize the surface morphology and structural properties of the ternary nanocomposite.The electrochemical performances of the composite were systematically investigated by CV,GCD and EIS.Compared to the other electrode materials,rGO/NiCo₂S₄/PAC-5 exhibits better electrochemical properties.At a current density of 1 A/g,its specific capacitance is 2462 F/g.Moreover,it has specific capacitance rentention of 93%after charging-discharging for 1000 cycles at a current density of 5 A/g.These results are attributed to the good syngeristic effect between rGO,NiCo₂S₄ and PAC in the rGO/NiCo₂S₄/PAC ternary composite.