Research On Controllable Preparation And Supercapacitance Performance Of Polyindole-based Composites

The development and utilization of modern renewable energy sources aimed at alleviating demand for fossil fuels is always combined with efficient energy storage systems.Among various energy storage technologies,supercapacitors have attracted a lot of attention due to the high power density,wide operating temperature range,long cycle life and environmental friendliness.However,limited by the low energy density,supercapacitors are still difficult to be widely used in continuous energy supply.The structure and properties of electrode materials are important factors affecting the charge storage capacity of supercapacitors.Therefore,it is of great significance to prepare electrode materials with rich porosity and high redox activity.Polyindole(PIn)is a special conductive polymer with characteristic aromatic ring structure,whose monomer is composed of a benzene ring and a pyrrole ring.Due to the good chemical stability,electrochemical reversibility and thermal stability,it has attracted extensive attention in the fields of sensors,catalysts,adsorbents,electrochromic and energy storage devices.However,in terms of supercapacitors,the fragile backbone and low conductivity limit its practical applications.It is shown that the preparation of PIn with different morphologies and structures by various synthetic methods,and the construction of PIn with carbonaceous materials or metal oxides/hydroxides is the key to enhance the supercapacitive performance.In this thesis,three PIn-based composites have been prepared by simple template method,emulsion polymerization method and solvothermal method.In addition,the compositions,microscopic morphologies and supercapacitive performance of as-prepared materials have been characterized and tested.The main contents of this thesis are as follows.(1)Nitrogen-doped porous carbon(NPC)with ordered pore distribution has been prepared by simple template method.By controlling the amount of NPC added,NPC@PIn composites with different morphologies have been successfully prepared using emulsion polymerization.The differences in their electrochemical properties have investigated.The results show that NPC@PIn composites have well-defined spherical structures with surface defects that shorten the diffusion pathway of electrolyte ions and provide a large number of electroactive sites.The specific capacitance of NPC@PIn-2 based electrode can reach 286.2 F g^-1 at a current density of 0.50 A g^-1 in 1.0 mol L^-1 H₂SO₄ solution.The specific capacitance retention is 88.9%after 3000 times of charge/discharge at a current density of 5.0 A g^-1,which is better than other control electrodes.In addition,the assembled NPC@PIn-2//Ti₃C₂Tx asymmetric supercapacitor has high energy density(30.4Wh kg^-1@750 W kg^-1)and excellent cycling stability(87.8%retention after 3000 cycles).(2)Using 3D cross-linked bacterial cellulose(BC)as template,PIn nanospheres have been grown in situ on BC fibers by emulsion polymerization.On this basis,nitrogen-doped carbon nanowires(NDCNWs)with a shape of"pearl necklaces"have been prepared by programmed warming pyrolysis.The results show that the 3D network interconnection structure and neat arrangement of carbon spheres increased the contact area between electroactive material and electrolyte,which effectively improved the specific capacitance.The NDCNWs-based electrode exhibits high specific capacitance(126.2 F g^-1@0.30 A g^-1)and excellent cycling stability(99.6%retention after 6000 charge/discharge cycles at a current density of 5.0 A g^-1)in 6.0 mol L^-1 KOH solution.In addition,the assembled symmetric supercapacitor has high capacitance(73.2 F g^-1@0.50 A g^-1)and excellent cycling stability(98.6%retention).(3)PIn/Ni Co-layered double hydroxide(PIn/Ni Co-LDH)nanocomposites have been prepared by emulsion polymerization and solvothermal methods.The results show that PIn/Ni Co-LDH microspheres are self-assembled from a large number of nanometer-thick flakes.The inter-cross-linked nanosheets with porous framework expose more redox active sites to promote rapid penetration of electrolyte solutions and provide sufficient ion transport channels.PIn/Ni Co-LDH-based electrode exhibits excellent electrochemical performance with high specific capacity of 294.3 m Ah g^-1 at a current density of 1.0 A g^-1.The specific capacitance retention is 83.9%after 2000 uninterrupted charge-discharge cycles at a current density of 5.0 A g^-1.The enhanced performance is attributed to the synergistic effect of Ni Co-LDH and PIn materials and the unique structure of the nanocomposite.In addition,the assembled PIn/Ni Co-LDH-2//AC asymmetric supercapacitor with activated carbon(AC)as the negative electrode has a high capacity(76.1 m Ah g^-1,1.0 A g^-1)and excellent cycling stability(85.8%of the initial capacitance retention after 3000 cycles).In summary,a series of PIn and its derivative materials have been synthesized by simple preparation methods in this thesis.By comparing the influence of composition,structure and morphology,investigating the electrochemical performance,and exploring the practical applications of as-prepared materials,it provides a broader idea for the preparation of PIn-based electrode materials and the assembly of supercapacitors.