Capacitance Performance Of Electrosynthesized Polyindole Bearing Electron-withdrawing Groups

Supercapacitors,a new,environmentally friendly and efficient energy storage system,which are designed to bridge the gap between batteries and capacitors,are able to store and deliver energy at relatively high rates.Electrode material is a key factor affecting the performance of supercapacitors.Conducting polymers have become a hot topic in supercapacitor field,because they have the merit of electrochemical reversibility,fast redox-activity,high conductivity,low toxicity,and low cost.Among conducting polymers,polyindole and its derivatives(polyindoles)have attracted great attention because of the similar high electrical conductivety,good stability,electrochemical reversibility with polypyrrole and similar high thermal stability,high redox activity with poly(p-phenylene).However,the study about polyindoles as electrode material of supercapacitor is still very scarce.At the same time,indole and its derivatives have many subsittuent groups,which may have effects on the structure,morphology and electrochemical properties of polyindole.This dissertation mainly focused on the electrosynthesis and capacitance performcane of indole and electron-withdrawing group substituted indoles in ACN/LiClO4(0.1 M).In addition,the effect of substituent group on the electrosynthesis of indole and the structure,thermal gravimetric behavior,morphology and capacitance performance of correspongding polymers were systematically investigated.1.Polyindole(PIn)film was prepared by electrodeposition method in ACN/LiClO4(0.1 M).Fourier transformation infrared spectroscopy confirmed that the polymerization occurred at the 2,3 position on the indole ring.The electrochemical capacitance properties of the PIn was investigated with cyclic voltammetry,galvanostatic charge-discharge,and electrochemical impedance spectroscope techniques.A specific capacitance of 86 F g-1 was obtained at a current density of 2.5 A g-1 in 1.0 M HClO4 solution.PIn presented an excellent cycle life with 90.8%specific capacitance retention after 1000 charge-discharge processes,which implied the good electrochemical stability of PIn.However,the specific capacitance of PIn still need to be enhanced.2.Poly(indole-5-carboxylic acid)(5-PICA),poly(indole-6-carboxylic acid)(6-PICA),and poly(indole-7-carboxylic acid)(7-PICA)nanowires were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4,whereas poly(indole-4-carboxylic acid)(4-PICA)was difficult to be obtained.The effects of carboxylic substituent position on their electrodeposition,morphology and capacitance properties were investigated for the first time.For 5-PICA,6-PICA and 7-PICA nanowires,the diameters of nanowires demonstrated by the scanning electron microscopy were about 100 nm,50 nm,and 30 nm,respectively.Their specific capacitances and energy densities in 1.0 M H2SO4 solution were measured to be 355 F g-1,383 F g-1,430 F g-1 at 2.5 A g-1 and 40.0,43.1,48.3 Wh kg-1 at a power density of 1125 W kg-1,respectively,and their specific capacitance retentions after 1000 charge/discharge processes reached 94.5%,95.1%,and 96%,respectively.These results indicated that the position of the carboxylic substituent had remarkable impacts on the diameter sizes and electrochemical properties of these polymer nanowires.Furthermore,the three polymers with high specific capacitance and excellent stability would be strong candidates as electrode material for supercapacitors.3.Poly(5-cyanoindole)(5-PCIn),poly(6-cyanoindole)(6-PCIn),and poly(7-cyanoindole)(7-PCIn)nanowires were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4,whereas poly(4-cyanoindole)(4-PCIn)was difficult to be obtained.The effects of cyano substituent position on their electrodeposition,morphology and capacitance properties were investigated for the first time.The result of scanning electron microscopy indicated that 5-PCIn,6-PCIn and 7-PCIn were consisted of nanowires network,and the morphlogy of 5-PCIn,6-PCIn showed more porous than 7-PCIn.Their specific capacitances and energy densities in 1.0 M HClO4 solution were measured to be 493 F g-1,302 F g-1,422 F g-1 at 2.5 A g-1 and 55.4,34.0,47.5 Wh kg-1 at a power density of 1125 W kg-1,respectively,and their specific capacitance retentions after 1000 charge/discharge processes reached 96.8%,89.4%,and 88.9%,respectively.These results indicated that the cyano substituent can significantly improve the electropolymerization of monomer and the morphlogy,electrochemical properties of corresponding polymer.Furthermore,the three polymers with high specific capacitance and excellent stability would be strong candidates as electrode material for supercapacitors.4.Poly(5-nitroindole)(5-PNI),poly(6-nitroindole)(6-PNI),and poly(7-nitroindole)(7-PNI)nanowires were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4.The effects of nitro substituent position on their electrodeposition,morphology and capacitance properties were investigated for the first time.The result of scanning electron microscopy indicated that 5-PNI,6-PNI and 7-PNI were consisted of nanowires network,and the morphlogy of 5-PNI,6-PNI showed more porous than 7-PNI.The thermal stability of 5-PNI and 6-PNI were better than 7-PNI.Their specific capacitances in 1.0 M HClO4 solution were measured to be 332 F g-1,93 F g-1,496 F g-1 at 2.5 A g-1 and when the current density increased to 25 A g-1,the specific capacitance decreased in the order of 5-PNI>7-PNI>6-PNI,and their specific capacitance retentions after 1000 charge/discharge processes reached 93.7%,95.7%and 61.8%,respectively.These results indicated that the position of the formyl substituent had remarkable impacts on the morphlogy,thermal stability and electrochemical properties of these polymer nanowires,and nitro substitutent can significantly improve the capacitance performance of polyindole,and nitro substituted polyindole have potential application in supercapacitor field.5.Poly(5-formylindole)(5-PFIn),poly(6-formylindole)(6-PFIn),and poly(7-formylindole)(7-PFIn)nanowires were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4,whereas poly(4-formylindole)(4-PFIn)was difficult to be obtained.The effects of formyl substituent position on their electrodeposition,morphology and capacitance properties were investigated for the first time.The result of scanning electron microscopy indicated that 5-PFIn,6-PFIn and 7-PFIn were consisted of nano wires network,and the morphlogy of 6-PFIn,7-PFIn showed more porous than 5-PFIn.The thermal stability of 5-PFIn and 7-PFIn were better than 6-PFIn.Their specific capacitances and energy densities in 1.0 M HClO4 solution were measured to be 402 F g-1,244 F g-1,489 F g-1 at 2.5 A g-1 and 35.7,21.7,43.5 Wh kg-1 at a power density of 1000 W kg-1,respectively,and their specific capacitance retentions after 1000 charge/discharge processes reached 95.4%,91.3%and 93.1%,respectively.These results indicated that the position of the formyl substituent had remarkable impacts and improvement on the morphlogy,thermal stability and electrochemical properties of polyindole.Furthermore,the three polymers with high specific capacitance and excellent stability would be strong candidates as electrode material for supercapacitors.