Robust graphene composite films for multifunctional electrochemical capacitors with an ultrawide range of areal mass loading toward high-rate frequency response and ultrahigh specific capacitance

The rapid development of portable electronics requires miniaturized and flexible electrochemical capacitors (ECs) with ultrafast frequency response and/or integrated high capacitive performance. Herein, we report such ECs based on the highly conductive films of reduced graphene oxide (rGO) and commercially available poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) prepared by blade coating or filtration. The typical EC with ultrathin film electrodes exhibited a high-rate frequency response (phase angle = -81.4°) at 120 Hz. On the other hand, ECs with freestanding thick film electrodes exhibited outstanding capacitive performance with a wide range linear relationship between areal capacitance and mass loading. Particularly, an ultrathick film electrode with mass loading up to 33 mg cm^-2 delivered ultrahigh areal (5365 mF cm^-2) and volumetric (203 F cm^-3) specific capacitances at 1 A g^-1 (33 mA cm^-2). The introduced wet-processing method perfectly integrates thin-film ECs for alternating current (AC) line-filtering and thick-film ECs for compact energy storage in one system, which is promising for practical applications.