Positional isomeric effect of nitro group substituted indoles on the electropolymerization and the capacitance performances of their polymers

The isomers of conducting polymers usually have different properties, however, there are still few studies on the isomeric effect of conducting polymers in supercapacitors field. In this work, four isomers (4-nitroindole, 5-nitroindole, 6-nitroindole, and 7-nitroindole) were selected as the research objects to study the positional isomeric effect of nitro group substituted indoles on the electropolymerization and the capacitance performances of their polymers. The results show that the prepared poly(5-nitroindole) (5-PNI) and poly(6-nitroindole) (6-PNI) are in nanowires structure, poly(7-nitroindole) (7-PNI) is in dense structure, while poly(4-nitroindole) (4-PNI) fails to be prepared. In addition, the as-prepared 5-PNI, 6-PNI nanowires and dense 7-PNI exhibit very different electrochemical properties and capacitance performances. Taking into account the specific capacitance (364 F g(-1) at 5 mV s(-1)), rate capability (58.5%) and cyclic stability (94% capacitance retention after 1000 cycles test), it can be concluded that 5-PNI is the most suitable electrode material in the field of supercapacitors.