Co-electrodeposited poly (3, 4-ethylenedioxythiophene) (PEDOT)-multiwall carbon nanotubes (MWCNT) hybrid electrodes based solid-state supercapacitors using ionic liquid gel electrolyte for energy storage with pulsed power capabilities

Abstract

Electrochemical and energy storage properties of poly(styrene sulfonate) doped poly (3, 4-ethylenedioxythiophene) (PEDOT:PSS) conducting polymer hybridized with the multiwall carbon nanotubes (MWCNT) are studied as solid-state supercapacitor with anion-doped ionic liquid (IL) gel electrolyte. The PEDOT: PSS-MWCNT composite electrodes were formed by co-electrodeposition using sequential 4 mA cm−2 current density with 10 ms current pulses in an aqueous medium with highly dispersed MWCNTs using Na-dodecyl sulfate (SDS) surfactant, PSS dopant (10–20 %) and EDOT monomer. Raman spectral study confirms with ≤10%PSS, the MWCNTs are moored into PEDOT chains via covalent bonding with carbons at α and β-position as PEDOT grows over flexible graphite substrate. Specific capacitance of 138 F g−1 discerned from cyclic voltammetry in IL-gel electrolyte is higher than reported in liquid electrolytes and chemically polymerized electrodes. Electrical double layer (EDL) capacitance analysis shows high 71.2 mF cm−2 contribution originated from MWCNTs with 10 % PSS, and slightly lower 48.8 mF cm−2 with 20 % PSS. The performance optimized PEDOT: PSS (10 %)- MWCNT (1 mg) based supercapacitors show large (43 %) access to the electroactive nanoporous surface regions contributing to capacitive charge and 57 % electrode has access to charge storage via diffusion limited Faradaic process. Nyquist plots analyzed for Warburg coefficient show minimal charge transfer resistance unimpacted by ionic diffusion. From the frequency response of the real and imaginary impedances pulsed power is assessed as 6.33 kW kg−1 at energy density 3.43 Wh kg−1. Charge-discharge behavior of optimized supercapacitor over 0.05–2.0 A g−1 current densities is triangular, highly symmetrical. Ragone plot shows high energy density of 7.7 Wh kg−1 at specific power 5.3 kW kg−1 plateauing out to 4.4 Wh kg−1 at higher specific power of 11.5 kW kg−1. Charge-discharge cycle analysis shows merely 20 % loss of specific capacitance by ∼500 cycles largely stabilizing for over 2000 cycles while the Coulomb efficiency remaining invariant at 95 %.