All-Solid-State Double-Layer Capacitors Using Binderless Reduced Graphene Oxide Thin Films Prepared by Bipolar Electrochemistry

Bipolar electrochemistry is used as an economical, single-step, and scalable process for the oxidation of a wireless graphite substrate, and the subsequent electrophoretic deposition of graphene oxide thin film on a second wireless substrate. An all-solid-state symmetric double-layer capacitor (EDLC) using binderless reduced graphene oxide electrodes exhibited outstanding reversibility and capacitance retention over 18000 cycles, as well as superior capacitive behavior at far-from-dc frequencies (for example 45 and 47 µ F cm-2), effective capacitances at 75 and 189 Hz, respectively (computed using a series resonance network with ideal inductors), compared to 55 µ F cm-2 at close-to-dc (computed from cyclic voltammetry at 10 mV s -1). This makes the device well-suited for ac filtering applications. A one-hour thermal treatment of the electrodes at 900 °C under vacuum increased the capacitance 13-fold (719 µ F cm-2) at close-to-dc, which decreased to 185 and 150 µ F cm -2 as the frequency was increased to 37 and 106 Hz, respectively These properties make this device suitable for both reasonable dc energy storage and higher frequency applications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim