Construction Of Universality And Performance Of A New Capacitor Based On Electroactive PILs-rGO Composite Material

The electrode material of the supercapacitors has a decisive influence on its power and energy density.Graphene nanosheets can not only provide high activity specific surface area for the electrochemical reaction of supercapacitors but also has a rapid transmission channel of ions or electrons in the horizontal direction of nanosheets,which is critical to improving the energy density of capacitors,achieving high specific capacitance and high rate performance.It is an important way to combine the pseudocapacitor material with graphene to improve the specific capacity of capacitors.Transition metal oxide and conductive polymer have higher theoretical specific capacitance than carbon materials,but the conductivity and stability need to be further improved.Therefore,the development of new integrated graphene composite electrode materials with high electrical conductivity,high active area and high specific capacity has always been a research focus.In this work,the universal construction strategy and application feasibility of electroactive polymerized ionic liquid-graphene composite electrode materials as the positive and negative electrodes in novel asymmetric supercapacitor are mainly studied based on the composition and structural characteristics of the new series of composite electrode materials.The main findings of the paper are as follows:1.The polymeric ionic liquid（PILs-rGO）modified reduced graphene oxide（rGO）is prepared.Graphene oxide（GO）is prepared by Hummers method,and polymeric ionic liquid 1-vinyl-3-ethyl-imidazole bromide[Poly（Vi Et Im⁺Br^-）,PILs]is prepared from 1-vinyl-3-ethyl-imidazole bromide monomer.PILs-rGO composite material is prepared through electrostatic and cationic-πinteractions between the PILs and rGO.The results of the physical characterization show that the PILs-rGO possesses a 2D thin sheet structure,indicating that the introduction of PILs can effectively suppress the stack of graphene nanosheets.The electrochemical properties of PILs-rGO composite materials are investigated by CV,EIS and GCD.In 2.5 M sulfuric acid solution,the specific capacitance of PILs-rGO electrode could reach 194.48 F·g^-1 at a current density of 0.88 A·g^-1,which is nearly 3.6 times compared to rGO(53.68 F·g^-1)electrode.2.The inorganic electroactive ions（IEA）with different oxidation and reduction potentials,such as[Fe（CN）₆]^4-and[PWA]^3-,are anchored onto the surface of the PILs-rGO nanocomposites based on the anionic exchange property of ionic liquids to construct a series of IEA/PILs-rGO composites.The results of the physical characterization show that the surface morphology of PILs-rGO matrix is not affected after the anion exchange,but the thickness of the nanosheets increase.The results of electrochemical tests indicate that the IEA/PILs-rGO composite materials exhibit additional capacitance compared to the PILs-rGO material,which should be originated from the electrochemical redox reactions of the IEA.An asymmetric capacitors with Fe（CN）₆^4-/PILs-rGO//CC as positive electrode and[PWA]^3-/PILs-rGO//CC composite as negative electrode are assembled,which possesses the mass capacitance of 110.18F·g^-1 and the area specific capacity of 94.67 m F·cm^-2 under the current density of 1.16A·g^-1(1 m A·cm^-2).When the current density increased ten times,the capacitor still shows the capacitance maintenance rate of 71.12%.Compared with the symmetric capacitor with PILs-rGO//CC as the anode and cathode,the asymmetric capacitor shows higher capacitance（the increase is about 1.7 times under the same current density）,lower self-discharge rate,good cycle stability and capacity retention rate.3.In order to further demonstrate the universality of the above preparation strategy,the organic electroactive ions（OEA）with different oxidation and reduction potentials,such as anthraquinone 2-sulfonate（AQS^-）and disodium 1,2-dihydroxybenzene-3,5disulfonate(BQDS^2-),are anchored onto the surface of the PILs-rGO nanocomposites to construct a series of OEA/PILs-rGO composites.The results of the physical characterization show that the AQS^-and BQDS^2-have been successfully anchored on the surface of PILs-rGO material,and the surface appearance,defects and hydrophilicity of the PILs-rGO based materials have not been affected significantly.The results of CV and GCD tests indicated that the OEA/PILs-rGO composite materials not only exhibit electrical double-layer capacitor provided by the PILs-rGO carbon materials,but also have the characteristics of Faradaic pseudocapacitance provided by the electroactive anions.Finally,an asymmetric capacitors with BQDS^2-/PILs-rGO//CC as positive electrode and AQS^-/PILs-rGO//CC composite as negative electrode are assembled.Compared with the symmetric capacitor with PILs-rGO//CC as both anode and cathode,the asymmetric capacitor shows higher capacitance（the increase was about 2.8 times under the same current density）and lower self-discharge rate.