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

Abstract

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.

Band‐Pass Filter and Relaxation Oscillator using Electric Double‐Layer Capacitor

“…Here we adopt the definition given by equation 1 since the targeted applications are in the frequency domain. The existence of an effective capacitance at high frequencies even though the impedance phase shift is not close to −90 ° suggests that the EDLC can be used in far‐from‐dc frequency applications ,,…”

“…A variety of other materials and fabrication methods have been explored to developing reliable supercapacitors of short response time . Nonetheless, although these fabricated devices exhibit superior frequency responses according to their spectral impedance phase angle or cyclic voltammetry features, the authors did not show their in‐operation performance when integrated in real far‐from‐dc applications ,,…”

All Fiber Based Electrochemical Capacitor towards Wearable AC Line Filters with Outstanding Rate Capability

“…In order to better compare the rate performance of SCs-1, SCs-2 and SCs-3, the plot of discharge current density is shown in Figure 3c. [42] More GCDs are shown in Figure S8. The galvanostatic charge-discharge (GCD) curves at 40 mA cm À 3 of SCs-1, SCs-2 and SCs-3 are shown in Figure 3d.…”

“…During discharging, the curves have no obvious voltage drop at different current density, ranging from 10 mA cm À 3 to 100 mA cm À 3 . [42] More GCDs are shown in Figure S8. Figure 4c shows the phase angle À 80°of SCs-3 at 120 Hz.…”

Ferroelectric Fractional‐Order Capacitors

“…Three integer values of α, −1, 0, and 1, lead to the pure inductor, pure resistor, or pure capacitor, respectively. If α takes non‐integer values, the element is called a fractional‐order element, which can also be described as a constant phase element with phase angle, . The concept of a fractional‐order element provides an additional degree of freedom in modeling, characterizing, and implementing novel circuit components in a wide spectrum of disciplines: viz .…”