Synthesis And Study Of Tar Based Porous Carbon Materials And Composite Materials For Supercapacitors

With the gradual exhaustion of fossil fuels,pursuing sustainable clean energy and developing advanced energy storage technologies has become a global goal.Among them,supercapacitors with high power density,long-cycle life and safe have attract widely public attentions.And the electrode materials are a key part for the performance of supercapacitors.Currently,the electrode materials can be divided into carbon materials(porous carbon,graphene,carbon nanotubes and carbon nanofibers),metal oxides(RuO2,MnO2,NiO and FeOx)and conductive polymers(PANi,PPy and PTh).Among them,porous carbons have advantages including low-cost,safety and longcycle life,but a low specific capacitance f porous carbon will restrict their wide applications.For metal oxides and conductive polymers,they all possess a high capacity,but bad cycling stability and rate capacity.Hence,in this work,different synthetic methods are used to prepare porous carbon and its composite materials to achieve both high capacity and good cycling stability.The main works are drawn as follows:(1)The bio-tar was used as precursor for preparation of porous carbon.Firstly,the different mass ratio of KOH/tar were investigated in preparation of porous carbon.When the mass ratio of KOH/tar is 4,the obtained porous carbon of AC-4 had highest specific surface area(2546 m2/g)and mesoporous volume of 1.54 cm3/g.Further,AC4 was used as an electrode material,which shows a high specific capacitance of 260 F/g at current density of 0.25 A/g.Then a symmetric electric double-layer capacitor was fabricated and exhibited a maximum density of 17.8 Wh/kg and maximum power density of 1247 W/kg.And this supercapacitor showed a good cycling stability of 90%of initial specific capacitance after 5000 cycles.(2)The bio-tar with high carbon content and viscous property was selected as a carbon resource.And utilizing the carbon deposition of nickel.The nickel foam can be coated by a slurry which was composited by tar,KOH and melamine and then further was carbonized and activated.After washing and drying,the NF@NPC with 3D carbon skeleton was obtained,the surface of which was porous.In next,the NiCo-LDH nanosheets were grown in the surface of porous carbon to produce NF@NPC@LDH with an electrodeposition method.By the electrochemical test,NF@NPC@LDH electrode shows a high areal capacitance(7924 mF/cm2)and a good rate capacity,which can be mainly attributed by that the carbon layer can stabilize LDH nanosheets so that they do not fall off in the process charging/discharging.Also,the 3D carbon skeleton can play a role in enhancing conductivity.The asymmetrical hybrid supercapacitor was assembled with NF@NPC@LDH electrode and NF@PC electrode,and showed maximum energy density of 1.6 mWh/cm3 and power density of 60 mW/cm3.And this supercapacitor exhibited a great cycling stability(90.9%retention).(3)The tar was selected as a carbon resource and K2FeO4 was used as an activating agent and an iron resource.The NF@Fe/Fe3O4/PC electrode without polymer binder and conductive agent was synthesized by a facile one-pot method and could be directly tested for electrochemical performance.And then the CVs of NF@Fe/Fe3O4/PC was tested in three different electrolytes(KOH and LiOH)and the contribution of diffusioncontrolled process and surface capacitive process for charge storage was analyzed.It can conclude that NF@Fe/Fe3O4/PC electrode showed a highest capacitive charge storage.It indicates the NF@Fe/Fe3O4/PC electrode showed better electrochemical performance(fast charging,long-cycle time and high-power density)in KOH electrolyte.And the NF@Fe/Fe3O4/PC electrode showed maximum areal capacitance of 3510 mF/cm2.A binder-free supercapacitor device was assembled with two identical NF@Fe/Fe3O4/PC electrodes and showed the maximum energy density of 0.42 mWh/cm3 and power density of 2 mW/cm3.73%of initial volume capacitance was retained after 5000 cycles,which indicated the device shows a good electrochemical stability.