Preparation of flexible conductive composite electrode film of PEDOT:PSS/Aramid nanofibers via vacuum-assisted filtration and acid post-treatment for efficient solid-state supercapacitor

A highly conductive and flexible composite film of Poly (3,4-ethylenedioxythiophene):polystyrene sulfonate and aramid nanofiber (PEDOT:PSS/ANFs) is prepared by vacuum-assisted filtration and post-treated by acid. The composite displays excellent mechanical integrity under bending together with flexibility, properties being attributed to the strong attachment of PEDOT:PSS onto the surface of the ANFs via hydrogen bonding and the ANF structure, respectively. The conductivity of the prepared composite is progressively enhanced by the post-treatment using sulfuric acids (1 M H2SO4 and 1.5 M H2SO4), reaching 20–25 times higher than that of untreated film. This enhancement is traced to the removal of the insulating PSS group together with an analyzable change in crystallization of the PEDOT:PSS component. However, excessive use of acid treatment is seen to reduce the mechanical strength, and, thus, ultimate loss of conductivity after frequent bending (up to 1000 times), only having 59% conductivity retention with high concentration acid treatment (1.5 M H2SO4) compared to a high conductivity retention of 95% with 1.0 M H2SO4. Adopting the relatively weaker acid enables a balance to be reached between these crucial factors of electrical conductivity versus mechanical integrity. The prepared film of PEDOT: PSS/ANFs treated by acid as an electrode of supercapacitor shows good electrochemical performances, including good volumetric specific capacitance (83.5 F/cm3 with 1.0 M H2SO4 and 75 F/cm3 with 1.5 M H2SO4 at 0.5 A/cm−3), cycle stability and capacitance retention of 83.3% and 87.5% after 2000 cycles, respectively. Furthermore, a solid flexible supercapacitor is finally assembled by the post-treatment of relatively low concentration acid with 1.0 M H2SO4. The configured supercapacitor displays excellent volumetric energy density of 23.44 mW h/cm2 (power density of 399.95 mW/cm2) at a very wide operating potential window of 0–1.6 V and cycle stability. Therefore, it is quite feasible method to fabricate a highly conductive and flexible composite film using PEDOT:PSS and ANFs by vacuum filtration and acid post-treatment, which expects to be a promising flexible composite electrode material applied in the preparation of energy storage devices.