Study On The Synthesis And Supercapacitor Performance Of Schiff Base-based Conductive Polymers

During the past few decades,the unprecedented rise in the utilization of flexible electronic products and electric vehicles have aroused enormous interest and concerns of scientists to develop new energy conversion and storage systems.Supercapacitors(SCs)are regarded as the most promising electrochemical storage system by virtue of their unique advantages(such as high-power density,long cycling life and high Coulombic efficiency).The electrode material of a supercapacitor is the vital factor affecting its electrochemical performance.The conducting polymers(CPs)are extensively explored for SCs application due to their lower cost as compared with the expensive metal oxides,high charge density and reversible Faradaic redox properties.However,poor cycle stability and low energy density are still important reasons that limit its large-scale commercial application.Thus,it is extremely urgent to develop a series of conducting polymer electrode materials that possess both high energy densities and ultra-long service life.In this thesis,the Schiff base-based conductive polymer was synthesized and the performance of its supercapacitor was studied.This thesis is divided into three parts,the main content is as follows:(1)We have synthesized Schiff base ligand L₁ with m-phenylenediamine and terephthalaldehyde as the reactant monomers,and then several Schiff base-based CPs(M-L_1,M=Al³⁺,Cr³⁺,Zn²⁺)were prepared by same stragegy.To characterize and analyze its morphology,structure and electrochemical properties with various instruments.The results show that the introduction of metal ions into the ligand L₁ framework will weaken the?-?stacking interactions,thereby reducing the crystallinity and thermal stability of the whole skeleton.However,as metal ions enter the organic framework,the specific surface area and pore volume of M-L₁are increased,which can provide more electroactive sites for the diffusion of electrolyte ions and the rapid transfer of electrons.In the three-electrode system,Al-L₁ can release a high specific capacity of 304.3 C/g at the current density of 0.5 A/g.After 1,000 GCD cycle,the capacity retention rate of Al-L₁ is still 60.8%(149.6 C/g),which is still higher than the initial capacity of ligand L₁.(2)We have synthesized Schiff base ligand L₂with 1,5-diaminonaphthalene and terephthalaldehyde as the reactant monomers,and then several Schiff base metal CPs(M-L₂,M=Al³⁺,Cr³⁺,Zn²⁺,Co²⁺,Ni²⁺)were prepared by same means.To characterize and analyze its morphology,structure and electrochemical properties by various instruments.The test results also show that the introduction of metal ions into the organic framework will weaken the?-?stacking interactions,making the structure of the M-L₂ tend to be disordered,and the mechanical stability and thermal stability will be reduced.The free-standing electrode results measured show that the specific capacity of the Cr-L₂ electrode at a current density of 0.5 A/g is 196.3 C/g.The assembled Cr-MOF//AC ASC device achieves an excellent energy density of51.9 Wh/kg at the power density of 370.1 W/kg along with a long-term life of 84.8%capacity retention after 10,000 GCD cycles.(3)The Cu-L₂@MWCNTs-X(X=0,2,5,10)composite materials was prepared by a step-by-step method,and their morphology,structure and electrochemical properties were characterized and analyzed.The test results show that the unique synergistic effect of the composite electrode material greatly improves its electrochemical performance.The Cu-L₂@MWCNTs-5 electrode maximum specific capacity of 492.6 C/g was obtained at the current density of 0.5 A/g in a three-electrode system.The electrode achieves outstanding cycling stability of 95.2%after 10,000 consecutive GCD cycles,as well as a high coulombic efficiency of nearly 100%during the test.The fabricated Cu-L2@MWCNTs-5//AC ASC device achieves the energy density of 44.01 Wh/kg at the power density of 8017.1 W/kg,even at the high specific power of 8017.1 W/kg with the specific energy of 28.06 Wh/kg(maintain 63.8%of the initial value).Moreover,the device also delivers a long cycle life with 92.6%capacity over10,000 repetitive GCD cycles.