Hydrotrope-driven facile synthesis of nanosized polyindole and their electrochemical study for supercapacitor application

To unleash the crude potential of polyindole (PIN), it is necessary to modify the polymerization technique in a way that a purer form of PIN is obtained with minimal pre- and post-processing. This work emphasizes the chemical oxidative polymerization of indole in the presence of a hydrotrope–tetra n-octyl ammonium bromide (TOAB), which acts as a phase transfer catalyst and encapsulating agent. The inclusion of TOAB resulted in a fine and uniform morphology of PIN with an average diameter of up to ± 100 nm. In addition, the physicochemical properties were analysed using X-ray diffraction and were in line with FESEM and FTIR analysis. The conjugated activity was also distinguished using UV–Vis. Furthermore, the synthesized PIN was also subjected to an electrochemical study, resulting in a higher specific capacitance in order of two or three magnitudes than those synthesized in the presence of a complete or partial organic solvent, or surfactants. To approve these results, a simple asymmetric supercapacitor was fabricated using as-synthesized PIN and activated carbon as electrode material to power electrical watch. The fabricated low-power energy storage device was able to keep the electronic watch on for more than 240 s, attesting the superior charge transfer and ion mobility. Hence, this work offers a new approach to synthesize PIN as binder-free electrode in aqueous mode and demonstrates a promising potential in several energy storage applications.