Systhesis And Electrochemical Properties Of Partially Graphitized Carbon/Transitional Metal Oxides Nanocomposite Using Chitosan As Precursors

Electrochemical capacitors,also known as supercapacitors,have been widely used in hybrid or pure electric vehicles,electronics,smart grid,railway,public transportation,aerospace and other fields due to their advantages such as fast charging and discharging,long cycle life,wide working temperature range,high power density,etc.The development of ideal electrode materials is one of the key factors to improve the capacitive property of supercapacitors.It is necessary to construct nano composite materials with good electrical conductivity,large specific surface area and wonderful electrochemical activity.Pure carbon electrode material has brilliant conductive performance,mechanical strength and a certain chemical stability.However,it does not have any redox activity,so it store energy mainly relying on electric double layer.As a kind of typical pseudocapacitor electrode material,transitional metal oxides?TMOs?own excellent redox activity,but they have low electrical conductivity and their volume easily expand or contract during charging and discharging process.To overcome these disadvantages,transitional metal oxides are usually combined with partially graphitized carbon with good electric conductivity.We choosed chitosan as carbon precursor,using it as a structure-directing agent to guide the growth of layered double hydroxides?LDHs?.After calcination,chitosan was converted into nitrogen doped partially graphitized carbon.The introduction of nitrogen atom caused the surface modification of carbon materials,resulting enhancement of wettability,thus increasing the effective contact area between electrolyte and electrode materials.Furthermore,nitrogen atom generated more pores and defects on the carbon surface,providing more active sites for redox reaction.The space and defects made great contribution to the porosity and specific surface area of the nitrogen doped partially graphitized carbon/transition metal oxides?N-PGC/TMOs?composite.Chitosan?CTS?,sodium dodecyl benzene sulfonate?SDBS?and CTS/SDBS mixture were used as structure directing agent to guide the growth of LDHs respectively in chapter 2.After calcination under N2 atmosphere and in the air continuously,porous nitrogen doped graphitized carbon/transition metal oxides composites were obtained.At the current density of 2 A?g^-1,N-PGC/CoFe-TMOs composite delivered a large discharge capacity of 671.1 F?g^-1,far higher than 283.3 F?g^-1 of pure cobalt iron oxides,indicating the typical synergistic effect between nitrogen-doped partially graphitized carbon and transition metal oxides.After 500 charge-discharge cycles at 2 A?g^-1,the capacitance retention reached 80.2%.Even at the high current density of 10 A?g^-1,N-PGC/CoFe-TMOs composite still remained a specific capacity of 573.3 F?g^-1.We prepared CTS/MN-NO₃ membrane by solvent evaporation method in chapter 3.After calcination under N2 atmosphere and in the air seperately,nitrogen doped partially graphitized carbon/transitional metal oxide composites were obtained.N-PGC/CoAl-TMOs delivered a large discharge capacity of 462.2 F?g^-1 at the current density of 2 A?g^-1,after 500 charge-discharge cycles at 2 A?g^-1,the capacitance retention reached 91.9%.Even at the high current density of 10 A?g^-1,N-PGC/CoAl-TMOs composite still remained a specific capacity of 424.6 F?g^-1.In chapter 4,3D-CTS/MN-NO₃ were prepared by freeze-drying method.After calcination under N2 atmosphere and in the air seperately,nitrogen doped partially graphitized carbon/transitional metal oxide composites were obtained.The N-PGC/CoFe-TMOs delivered a large discharge capacity of 897.8 F?g^-1 at the current density of 2 A?g^-1.After 500 charge-discharge cycles at 2 A?g^-1,the capacitance retention was 80.8%.Even at the high current density of 10 A?g^-1,the specific capacity of N-PGC/CoFe-TMOs composite was 632.1 F?g^-1.Experimental results showed that the derived carbon material was successfully doped with nitrogen in situ.The products were all partially nitrogen doped graphitized carbon/double metal oxides composites.Metal oxides successfully suppressed the aggregation of graphite carbon layer.The variety,concentration of metal elements and the calcination temperature had crucial effects on the structure and properties of the products.We explored a simple,controllable and universal method to prepare nitrogen doped partially graphitized carbon/transition metal oxides composite,which can be used as a promising electrode material of supercapacitor.