Structural Modulation of Exfoliated Graphene via a Facile Postultrasonication Treatment toward Enhanced Electrochemical Properties of Supercapacitor Electrode

Abstract

Graphene has been gaining tremendous attention as an active material for energy storage devices owing to its large surface area, high electrical conductivity, and high electrochemical stability. However, the restacking of graphene layers during the synthesis process has become one issue that can reduce electrode performance. In this work, the structure of electro-exfoliated graphene (EG) is regulated to improve its electrochemical properties as the supercapacitor electrode using a facile postultrasonication treatment. The ultrasonicated EG exhibited a higher exfoliation degree than the raw EG as indicated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and Brunauer–Emmett–Teller (BET) characterization results. Ultrasonicated samples were then tested using three-electrode configuration, which obtained a maximum specific capacitance of 140.5 F g–1 at 0.5 A g–1, which is higher than that of the sample prepared without ultrasonication treatment (79.0 F g–1) at the same current density. Moreover, the cycling performance of ultrasonicated EG was examined using two-electrode measurement yielding the highest capacitance retention of 92.9% after 10,000 cycles at 1 A g–1, which can improve the stability of EG than the sample without ultrasonication (82.2%). These results indicate that ultrasonication can be applied as a straightforward treatment to modify exfoliation degree and lateral size of EG sheets leading to the enhancement of supercapacitor electrode performance.

One-Step Synthesis of Fragment-Reduced Graphene Oxide as an Electrode Material for Supercapacitors

“…The tested potential window ranges from 0 to 1 V (vs SCE). The electrochemical impedance spectroscopy (EIS) measurements were conducted in an open-circuit potential over a frequency range from 0.1 to 100 kHz at a voltage amplitude of 0.01 V. The specific capacitance C (F/g) value measured by GCD in the three-electrode system was obtained according to the following equation: ,,, C = I · normalΔ t m · normalΔ V where I (A) is the value of constant current in GCD measurement, Δ t (s) is the total time of the discharge part, m (g) is the mass of graphene material on the WE, and Δ V (V) is the voltage change during discharge.…”

“…In a two-electrode system, the specific capacitance C sp (F/g) of a single electrode was computed from the discharge part of the GCD curve used by the following equation: ,,, C sp = 4 · C cell = 4 I · normalΔ t M · normalΔ V where C cell (F/g) is the specific capacitance of the cell, I (A) is the value of constant current in GCD measurement, Δ t (s) is the total time of the discharge part, M (g) is the mass of FrGO material on two electrodes, and Δ V (V) is the voltage change during discharge.…”

“…More OCFGs could provide large pseudocapacitance, and the macroporous structure could shorten the electron/ion transport path . Some researchers have reported that the particular morphology of electrode materials can enhance specific capacitance. − Abdillah et al pointed out that the smaller sheet size, due to the shorter ion diffusion path and lower ion diffusion resistance, contributes to easier ion penetration into the active sites . Therefore, it is still challenging to develop a novel synthetic method to obtain high retention of OCFGs, small particle size, and macroporous structured graphene materials at low temperatures, and apply as an electrode material to SCs to obtain excellent specific capacitance.…”

“…39−41 Abdillah et al pointed out that the smaller sheet size, due to the shorter ion diffusion path and lower ion diffusion resistance, contributes to easier ion penetration into the active sites. 41 Therefore, it is still challenging to develop a novel synthetic method to obtain high retention of OCFGs, small particle size, and macroporous structured graphene materials at low temperatures, and apply as an electrode material to SCs to obtain excellent specific capacitance.…”

Novel strategy for high-performance supercapacitors through the polyvinylpyrrolidone (PVP)-assisted in situ growth of FeS2

“…23,26,27 It should be noted that such nanostructuring also offers flexibility and short diffusion path lengths for ions, which are beneficial for the supercapacitor performance and for preventing dendritic reactions. 4,26,[28][29][30] Previously, several methods, such as hydrothermal and solvothermal methods, have been proposed for obtaining smaller pyrite sizes to increase the supercapacitor performance. [31][32][33][34] However, these synthesis processes still lead to a large particle size, which is insufficient for achieving highperformance supercapacitors.…”