Substitution effects of cyano group on the electropolymerization, thermal stability, morphology, and supercapacitor performance of indole based polymers

Substitution effects significantly impact the electropolymerization, morphology, properties and electrochemical performance of conducting polymers. In this work, the substitution effects of the electron-withdrawing cyano group on indole polymers are studied in detail. Polyindole (PIn) and its three cyano group substituted derivatives, i.e., poly(5-cyanoindole) (P5CIn), poly(6-cyanoindole) (P6CIn), and poly(7-cyanoindole) (P7CIn), are successfully electrosynthesized in 0.1 M LiClO4/acetonitrile, while it is difficult to electrodeposit 4-cyanoindole into polymer due to the steric effects. Scanning electron microscopic images reveal that P5CIn, P6CIn, and P7CIn have nanofiber structures, while PIn has a dense and cracked structure. Furthermore, P5CIn displays the best capacitance performance with a specific capacitance of 493 F g-1 at 2.5 A g-1, and 87.1% capacitance retention after 5000 cycles charge/discharge. A detailed study of cyano-substituted PIn is provided by this work and it also presents a kind of high-performance supercapacitor material.