Redox additive enhanced capacitance: Multi-walled carbon nanotubes/polyaniline nanocomposite based symmetric supercapacitors for rapid charge storage

In the present study, we report all-solid-state high energy density symmetric supercapacitors based on partially exfoliated multi-walled carbon nanotubes (Px-MWCNT)/Polyaniline (PANI) nanocomposites with redox-active polymer gel as an electrolyte/separator. Fabrication of mechanically stable polymer gel electrolyte with high ionic conductivity, excellent compatibility with the active material, and long cycle life is pivotal to obtain superior electrochemical performance for flexible solid-state supercapacitor devices. An organically reversible redox-active (hydroquinone-HQ) non-covalent approach adopted to achieve the significant enhancement in specific capacitance. The highest specific capacitance of 186.1, 809.6 and 644.4 F g(-1) was achieved at 25 mV s-1 for Px-MWCNT, Px-MWCNT/PANI and PANI based symmetric supercapacitor cells, respectively. The enhancement in capacitance was found to be increased in the order of 82.5%, 129% and 34.3% for Px-MWCNT, Px-MWCNT/PANI, and PANI respectively when compared with devices lacking in redox-active HQ. Moreover, incorporation of redox-active HQ transforms the pseudocapacitance to battery-type behavior. The polymer grafted morphology of nanocomposite (Px-MWCNT/PANI) in 1:1 wt ratio as an electrode material with redoxactive gel polymer electrolyte exhibits synergistic effect in specific capacitance enhancement with excellent charge-discharge rate capability and electrochemical stability (78% capacitive retention after 2000 cycles) than pure PANI (69.4% capacitive retention after 2000 cycles) based supercapacitor.