Design And Synthesis Of Quinone Groups Functionalized Carbonaceous Material For Asymmetric Supercapacitors

To date,among every reported electrochemical energy storage system,the supercapacitor has shown a prominent power density than primary or secondary battery,while a higher energy density than conventional physical capacitor,and simultaneously exhibits an excellent cycle stability.It emergence faultlessly fill the gap between the traditional physical capacitor and the secondary battery.But how to enhance the energy density of a supercapacitor and without sacrificing its high power density and long cycle life to meet the accelerated market requirement,becomes a bottleneck to restrict its widely applied.From the energy density calculation formula for a supercapacitor?E=0.5 CV²?,it can be seen that increasing the specific capacitance?C?of the electrode material or broadening the cell voltage?V?of the device can directly improve its energy density.In this dissertation,we set a higher energy density as our ultimate goal and mainly studied two aspects as following:firstly,using electrochemical redox active organic small molecules as guest molecules,noncovalent modifies various types of carbon-based materials and further changes their surface properties.As a result,the electrochemical capacitance is superimposed on the electric double layer capacitor,and increasing the total specific capacitance of the electrode material;secondly,assembling an asymmetric supercapacitor by using positive and negative electrode materials whichpossess an excellent electrochemical performance.In the electrochemical test process,the two electrodes will generate favorable potential self-matching behavior,and further obtains a large voltage in an aqueous electrolyte.The specific research contents are shown as follows:?1?Chemical oxidation is employed to lengthwise unzip and transverse cut Multi-walled carbon nanotubes?MWCNTs?to form a special-shaped structure carbon nanotubes?SCNTs?that are residual tubes with randomly distributed graphene layers on the tube wall.Then,we coat polyaniline nanoparticles on SCNTs through in-suit polymerization,in which the SCNTs are served as core and polyaniline is regarded as shell.The resultant core-shell structure is converted to a nitrogen-doped heterostructure carbon?NHC?through pyrolysis by following alkali activation.Subsequently,theNHCisusedasconductivesubstratetoadsorb tetrachlorobenzoquinone?TCBQ?and anthraquinone?AQ?molecules via?-?stacking interaction to get the functionalized nitrogen-doped heterostructure carbon?TCBQ-NHC and AQ-NHC?,respectively.As a result,multielectron reactions in positive and negative potential ranges are implanted in two electrodes,respectively.Electrochemical measurements show that the TCBQ-NHC and AQ-NHC electrodes achieve specific capacitances of 365 and 331 F g^-1 at 1 A g^-1 in potential windows of0-1.0and-0.4-0.6V,respectively.Furthermore,theas-constructed AQ-NHC//TCBQ-NHC asymmetric supercapacitor?ASC?can deliver high energy density(20.3 Wh kg^-1)at the power density of 0.7 kW kg^-1 with long cycle life?the capacitance remains 98%of the initial value after 5000 cycles?.?2?Metal-organic frameworks?MOFs?have been turned out to be an excellently self-sacrificing template for preparing porous carbon.Herein,we synthesized a nitrogen-doped porous carbon materials?NPCs?by direct thermolysis of zinc-based MOFs?ZIF-8?.Fortunately,the NPCs with high specific surface area and abundant pore structure was suitable for using as conductive substrate to anchor organic molecules.Anthraquinone?AQ?,1,4-naphthoquinone?NQ?and tetrachlorobenzoquinone?TCBQ?were selected to functionalize NPCs via noncovalent interactions,respectively.As a consequence,the multielectron redox centers possessed by AQ,NQ and TCBQ were implanted in the NPCs.More interestingly,the electrochemical rate-determining step for the functionalized NPCs was surface process rather than diffusion,which is similar to capacitive behavior of the electrical double layer.The functionalized NPCs revealed an enhanced overall capacitance?about 1.4 times higher than NPCs?because the electrochemical capacitance was superposed on the electrical double layer capacitance.Furthermore,the as-assembled asymmetrical supercapacitor?ASC?exhibited excellent energy storage performance.The topological structure of MOFs skeleton and the potential self-matching behavior between the positive and negative electrodes were responsible for high energy density(23.5 Wh kg^-1 at 0.7 kW kg^-1,which is 1.54 times higher than that of NPCs symmetrical supercapacitor)of the device.?3?The RuO₂/graphene hydrogel composite?RuO₂/SGH?was synthesized through simple hydrothermal method by using oxidized graphite?GO?and RuCl₃ as raw materials.Then,1,4-naphthoquinone?NQ?was selected to functionalize the exposed graphene hydrogel to prepare the organic molecular functionalized RuO₂/SGH electrode materials?NQ-RuO₂/SGH?.As a consequence,the inorganic materials and organic materials were successfully combined together.The electrochemical test showed that the composite material could still exhibits a high specific capacitance(451 F g^-1)even though at low a RuO₂ loading mass?14.6%?,which was preliminarily proved that the organic electrode material can provide a superexcellent opportunity for the green energy storage.In addition,a nitrogen-doped porous carbon material?MNC?was prepared by one-pot method by using mushroom as carbon source,melamine as nitrogen source and ZnCl₂ as activator.Then,we regarded MNC as the negative electrode material and NQ-RuO₂/SGH as positive material to assemble an asymmetric supercapacitors.The electrochemical test showed that the energy density of the capacitor in the 1 M H₂SO₄ electrolyte is 16.3 Wh kg^-1.