Template free one step synthesis of polyindole microspheres for binder-less electrochemical capacitors

Polyindole microspheres were synthesized by a simple one step rapid mixing polymerization method without using any template or surfactant. As synthesized polyindole microspheres were further doped with HClO4 which results the broken microspheres with improved performance as electrode material in electrochemical capacitors. After thorough characterization of the synthesized materials, electrodes were fabricated by using water as medium without any binder where morphologies of the electrode materials were preserved. To compare the results, another set of electrodes were prepared replacing water by NMP as the electrode preparing medium, where the microspheres and broken microspheres of polyindole and doped polyindole were destroyed due to the dissolution of materials in NMP. All electrodes were characterized by using 3 electrode cells with 1 M H2SO4 as electrolyte and Ag/AgCl as reference electrode to determine the specific capacitance, specific energy and specific power of the electrode materials. The specific capacitance values obtained for polyindole microspheres by using water and NMP as media for electrode preparation were 116 F g−1 and 72 F g−1 respectively whereas the corresponding values for doped polyindole were 153 F g−1and 90 F g−1 respectively at the current density of 1 A g−1. The cyclic stability calculated for polyindole microsphere and doped polyindole broken microsphere electrodes using water as medium of electrode preparation were 80 % and 87 % retention of initial values of specific capacitance after 5000 charge-discharge cycles, respectively. Finally all-solid-state symmetric electrochemical capacitor devices were fabricated by using all four types of electrodes with PVA/H2SO4 gel electrolyte. Another advantage of this approach is that for both the materials no binders were used for electrode preparation.