Synthesis And Electrochemical Properties Of Carbon-based Nanocomposites

Carbon-based nanocomposites are one of the hot research topics in the field of energy storage owing to rich source,low cost,high conductivity,good stability,low density,and safety and environmental protection.However,it is difficult to meet the requirements for the use of high-power electrical equipment due to low specific capacity,limited further application.Carbon and its composites are one of electrode materials for supercapacitors.The performance of the enery storage device is affected by the morphology,pore structure,specific surface area,surface chemical properties,and electrical conductivity of the electrode material.Thus,the exploration of carbon-based composites with high specific-capacity through structure and composition design is considered to be an effective means to improve the electrochemical properties of supercapacitors.This dissertation focuses on the synthesis and electrochemical properties of carbon-based nanocomposites with different compositions and structures.The carbon-based nanocomposites include activated carbon fibers-tungsten disulfide nanocomposites,activated carbon fibers-sodium titanate nanocomposites,activated carbon fibers-graphene nanocomposites,and graphene-Prussian blue analogue nanocomposites.The main research contents of this thesis are as follows:(1)The activated carbon fiber based on polyacrylonitrile was obtained through electrospinning and following carbonized/activated one-shot method.The activated carbon fiber-tungsten disulfide nanocomposite(ACF-WS2)was synthesized by hydrothermal method,and exhibiting both double electric layer capacitive behavior and psudocapacitive behavior.The SEM images show that the tungsten disulfide nanosheets with the thickness of about 20 nm were immobilized on the surface of activated carbon fiber.The specific surface area of activated carbon fiber-tungsten disulfide nanocomposite was as low as 10.8 m2 g-1.An asymmetric quasi-solid state supercapacitor was assembled using the activated carbon fiber as an anode and the activated carbon fiber/tungsten disulfide nanocomposite as a cathode,showing the mass specific capacity of 254.6 F g-1(volume specific capacity is 550 F cm-3)at 1 A g-1 in PVA/KOH gel electrolyte.The higher specific surface area of activated carbon fiber-tungsten disulfide nanocomposite was synthesized by the introduction of triblock copolymer of F127 during the hydrothermal process based on the above results.The resulted activated carbon fiber-porous tungsten disulfide nanocomposite(ACF-WS2-P)shows the high specific surface area of 72.3 m2 g-1.An asymmetric sodium hybrid capacitor was assembled using the activated carbon fiber as a cathode and the activated carbon fiber-porous tungsten disulfide nanocomposite as an anode,showing the mass specific capacity of 166.89 F g-1 at 1 A g-1 and the mass specific capacity of 76 F g-1 at 15 A g-1.(2)Using the above activated carbon fiber as a support material,sodium titanate(Na2Ti3O7)nanosheets were synthesized in situ on the surface of activated carbon fiber by a hydrothermal method,and obtaining activated carbon fiber-sodium titanate nanocomposite(ACF-NTO).The SEM images show that the stacking of sodium titanate nanosheets can be effectively inhibited by the activated carbon fibers.A sodium ion hybrid capacitor is assembled using the activated carbon fiber as cathode and the activated carbon fiber-sodium titanate composite as anode,and showing the specific capacitor of 76.8 F g-1 at 1 Ag-1 and 36 F g-1 at 10 A g-1.(3)Graphene oxide was prepared by Hummers' method,and then was reduced using zinc foil within the weak acid.Simultaneously,the activated carbon fiber-reduced graphene oxide composite was synthesized by self-assembly in room temperature conditions.Then,the sample was fully immersed in a saturated urea solution,and followed by freeze-dried,heat treatment.Finally,target material(ACF-rGO-N)with 11.89 at.%of the nitrogen content was fabricated.The SEM images show that the reduced grapheme oxide can be embedded in the gap of activated carbon fiber with a uniform diameter of about 300 nm.The symmetrical quasi-solid state supercapacitor based on the activated carbon fiber/reduced grapheme oxide composite shows the he specific capacity of 254 F g-1 at 0.2 A g-1 and 176 F g-1 at 10 A g-1 in the PVA/KOH gel electrolyte.Moreover,the specific capacity retention can be upto 99%after 10 000 cycles at the current density of 3 A g-1.(4)The reduced graphene oxide-Prussian blue analogue(rGO-NiHCF)was synthesized by inverse microemulsion method.The SEM images show that the agglomeration of the nickel hexacyferrate can be effectively inhibited by the reduced grapheme oxide.The ingenious structure exhibits the high specific surface area,and improves the electrochemical performance.The specific capacity can be up to 415 F g-1 at 0.2 A g-1 and 386 F g-1 at 10 A g-1 in 0.5 M Na2SO4 under the three-electrode system.Further,the reduced graphene oxide/nickel-cobalt hexacyanoferrate nanocomposit(rGO/Ni-CoHCF)was synthesized by inverse microemulsion method to improve the electrochemical properties of the reduced graphene oxide-Prussian blue analogue nanocomposites.The experimental results confirm that the chemical combination can be formed between the reduced graphene oxide and double metal hexacyanoferrate.The reduced graphene/nickel-cobalt hexacyanoferrate nanocomposite shows the specific capacity of 466 F g-1 at 0.2 A g-1 in 0.5 M Na2SO4 under the three-electrode system.In addition,the sodium ion half battery using the resulting materials as cathode and sodium foil as counter electrode exhibits the capacity of 118 mAh g-1 at 0.1 A g-1.