Modification Of Enviroment Originated Carbon-based Supercapacitors And Their Performance

For a long time,the survival and development of human being is heavily relied on fossil fuel.In order to solve this dilemma,pepole develop a series of new energy sources,such as solar energy,wind energy and bioenergy.But energy storage became an urgent problem.Later then,lithium battery and supercapacitors come into being,which is becoming more and more popular in the field of electronic equipment and hybrid cars due to its quick charge-discharge,long cycle life and so on.Based on the different energy storage mechanism,electrode materials used for supercapacitors can be divided into two categories:biochar and graphene,as the representative double layer capacitors materials and polyaniline(PANI),which on the behalf of pseudocapacitors materials.Main works of this study focued on graphene/PANI matrix composite and N-doped carbon derive from sewage sludge.The main contents are as follows:(1)In-situ polymerization has the advantages of simplicity and low cost.First,graphene hydrogels was prepared by hydrothermal method.Then,we optimize the confined space by sheeter to adjusting the pressure.Finally,Graphene/PANI was prepared by oxidative polymerization of aniline between graphene nanosheets.The composite was analysed by SEM,XRD and Raman to confirm that PANI nanowires was grew up in the space between graphene nanosheets.Graphene/PANI composite material can be used as the electrode.Due to the synergistic effect between graphene and PANI,the composite show high capacitance about 542 F/g at a current density of 0.2 A/g,good rate performance and long cycle stability.Furthermore,Graphene/PANI composite material show low capacitance of about 8%after 1000 cycles at the current density of 1 A/g.(2)Hierarchical nitrogen doped porous carbons(HNPC)was prepared from biomass-derived sludge via a cost-effective two-step carbonization and the subsequent alkali activation.To study the structure,morphology and electrochemical properties of the hierarchical nitrogen doped porous carbons,nitrogen doped porous carbons was prepared under different carbonization temperature.After experiment,we can conclude that nitrogen functional groups on the carbon skeleton of HNPC can enhance the surface wettability.Furthermore,the existence of nitrogen heteroatom can improve the capacitance by increasing surface defects and active sites.It is interesting to find out that the obtained HNPC demonstrates ordered pore structure from the surface into the entire structure that was originated from the KOH activation process.The as-synthesized HNPC exhibits N-doped and hierarchically structures,which make them ideal candidates for high performance supercapacitors.As a result,the as prepared HNPC demonstrated superior specific capacitance(582 F/g at 100 mA/g)and excellent rate performance in 6 M KOH.Furthermore,the as-synthesized HNPC-600 exhibited a superior capacitance retention performance.A greater than 90%retention of the initial capacitance was obtained after 10000 charge/discharge cycles at a current density of 1 A/g,which indicated its excellent cycling stability.