Effect of substituent position on electrodeposition, morphology, and capacitance performance of polyindole bearing a carboxylic group

In this paper, the effects of carboxylic substituent position on their electrodeposition, morphology and capacitance properties were investigated for the first time. The results indicated that three carboxylic group substituted polyindole derivatives nanowires, namely poly(indole-5-carboxylic acid) (5-PICA), poly(indole-6-carboxylic acid) (6-PICA), and poly(indole-7-carboxylic acid) (7-PICA), were successfully electrochemically synthesized in acetonitrile containing 0.1 M LiClO4, whereas poly(indole-4-carboxylic acid) (4-PICA) was difficult to be obtained. 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. (C) 2015 Elsevier Ltd. All rights reserved.