Development of pseudo-surface modification method for graphene

In recent years, it cannot be denied that it is more difficult to imagine spending a day without the help of electronic devices in modern technologies. However, these devices consume power and generate intense heat, and caused low efficiency and performance. Therefore, thermally conductive polymer composites for electronic devices is generating a lot of interest in various fields. Recently, graphene has attracted enormous attention owing to its remarkable properties. It is flexible, lightweight, ultra-strong, and highly conductive in both electrically and thermally. However, due to high surface area, van der Waals and π- π interactions, graphene sheets tend to aggregate and cause dispersion problem in solvents, resulting limit applications. Herein, pseudo-surface modification is proposed, which is a non-covalent modification method, which can maximally preserve graphene’s natural structure and its inherent properties. In this study, this facile and cost-efficient way was used to prepare functionalized GO (fGO), which involving aromatic hydrocarbons in polymerization; 2-naphthalene thiol (2-NT) acted as chain transfer agent in radical polymerization with MMA, while 1-naphthalene methanol (1-NM) acted as aromatic agent in ring opening polymerization with ε-CL. SEC profiles and NMR spectra indicated the attachment of aromatic agent on polymer chains. Both fGO showed good dispersion in more solvents compared to GO. In term of thermal conductivity, 0.35wt% fGO-PCL showed 43% improvement compared to PCL with 1-NM. While, 5wt% fGO-PMMA showed 25% improvement compared to PMMA with 2-NT. In summary, proposed pseudo-surface modification able to synthesis fGO with better dispersion and thermal conductivity for applications in electronic devices

Electro-exfoliating graphene from graphite for direct fabrication of supercapacitor

A facile production of graphene via electro-exfoliation is demonstrated using different types of oxidizing agent (HNO3, NaNO3, H2SO4 and H2O2) in the presence of sodium dodecylbenzenesulfonate as a surfactant. Different types of surfactant–oxidizing agent solutions in different concentrations significantly influenced the electrochemical exfoliation of graphite rod. The surface morphology, layer thickness and defects of the as-produced graphene are further evaluated. Additionally, the as-produced graphene is fabricated as a supercapacitor electrode via direct vacuum filtration. Nylon membrane and polymer gel, each containing 2.0 M of potassium hydroxide, are utilized to investigate the influence of the electrolyte type on the capacitance performance. Upon 1000 charge/discharge cycles, the nylon membrane electrolyte recorded capacitance retention of 94%, whereas the polymer gel electrolyte recorded an impressive capacitance retention that exceeded 100%. The potential of the fabricated supercapacitor for real applications is manifested by its ability to light up a light-emitting diode upon charging

Microwave exfoliated graphene-based materials for flexible solid-state supercapacitor

Herein, we report the simultaneous exfoliation and reduction of graphene oxide (GO) and graphene nanoplatelets (GNPs) by rapid microwave irradiation, to overcome the hurdles of their low electrical conductivity and tendency to restack, and realize their full potential as supercapacitor electrode materials. After microwave treatment, the ID/IG value of the microwaved GO (MW-GO) increased by 0.11, whereas the I2D/IG value of the microwaved GNPs (MW-GNPs) decreased by 0.48, revealing that the graphene-based materials were reduced and exfoliated as observed in the Raman spectra. Morphological studies revealed a porous structure of MW-GO and loose stacked layers of MW-GNPs, which showed the exfoliation of the graphene-based materials. A supercapacitor device was constructed using a mixture of MW-GO, MW-GNPs, and polypyrrole and yielded a specific capacitance value of 137.2 F g−1 with a cycling stability of 89.8% after 1000 charge/discharge cycles. The electrochemical performance of the device remains unchanged when bent continuously at 180° because the cyclic voltammetry and galvanostatic charge/discharge curves remained the same after 50 bending repetitions. Therefore, the simultaneous reduction and exfoliation of these graphene-based materials by rapid microwaves provides a promising route for the scalable and cost-effective preparation of supercapacitor electrode materials

Fabrication of graphene-based flexible supercapacitors in planar- and fiber-structured configurations

With the emergence of flexible electronic devices, flexible supercapacitors have attracted widespread interest in developing lightweight, thin and efficient portable/wearable energy storage devices. Along with the general information about flexible supercapacitors, this thesis focuses on flexible supercapacitors including the planar-structured flexible supercapacitors as well as the new-type fiber supercapacitors. Thus, in this thesis, the construction of electroactive materials on the flexible substrates and feasible strategies to achieve highperformance flexible supercapacitors were discussed. In the planar-structured flexible supercapacitors, aluminium carbide was being employed as a current collector, where it is light, thin and highly flexible. The simultaneous exfoliation and reduction of graphene-based materials by rapid microwave irradiation were employed to generate a microwave graphene mix (MGM). To demonstrate the supercapacitors application, a supercapacitor device were constructed and yielded a specific capacitance value of 78.1 F g-1 using a solid-state electrolyte with excellent cycling stability of 93.8% after 1000 cycles of charge/discharge. Then, the as-prepared MGM was mixed with polypyrrole (PPy) to further enhance the electrochemical performance. A supercapacitor device using MGM-PPy as an electroactive material recorded a specific capacitance value of 137.2 F g-1 which is 1.8 times higher than that of MGM with cycling stability of 89.9% after 1000 cycles of charge/discharge. Different from the planar-structured supercapacitors, the fiber-structured was fabricated through a simple electrochemical deposition process of polypyrrole/reduced graphene oxide onto the surface of carbon bundle fiber. The surface morphology revealed a high degree of porosity in the PPy-rGO-2 composite; facilitating the ionic penetration, leading to an excellent electrochemical performance. The PPy-rGO-2 exhibits good electrochemical performance (96.2 F g-1) with an energy density of 13.4 Wh kg-1 and a power density of 322.9 W kg-1. However, after a series of charging-discharging cycles, the electrochemical performances of the PPy-rGO-2 deteriorated due to the changes in the structural properties such as the reduction in pore size, and transformation of the structure of rGO from amorphous to graphitic. To investigate the mechanical bendability/flexibility of the as-fabricated supercapacitor devices, both planar- and fiber-structured supercapacitor devices were bent at various angles and revealed that the bending had nearly no effect on the specific capacitance values. The combination of solid-state electrolyte and flexible current collector with flexible free-standing electroactive materials made up of graphene-based materials and PPy, capable of withstanding stress with no drastic changes in its electrochemical performance, demonstrating an excellent mechanical bendability. Overall, the sustainable electrochemical performance, mechanical flexibility, low-cost and lightweight, flexible supercapacitors are undoubtedly emerging as promising renewable energy technology for future energy storage systems

Electrochemical performances of flexible solid-state fibre supercapacitor based on polypyrrole/ reduced graphene oxide

A flexible solid-state fibre supercapacitor was fabricated through a simple electrochemical deposition process of polypyrrole/reduced graphene oxide (PPy/rGO) onto the surface of carbon bundle fibre, using polyvinyl alcohol enriched with potassium hydroxide as a solid-state electrolyte. The surface morphology revealed a high degree of porosity in the PPy/rGO composite; facilitating the ionic penetration, leading to an excellent electrochemical performance. The fabricated supercapacitor recorded a specific capacitance of 96.16 F g-1, with an energy density of 13.35 Wh kg-1 and a power density of 322.85 W kg-1. It showed remarkable pliability at various angles as evidenced by the shape of the cyclic voltammetry curves that remained unchanged. After a series of charging-discharging cycles, the electrochemical performances of the supercapacitor deteriorated due to the changes in the structural properties such as the reduction in pore size, and transformation of the structure of rGO from amorphous to graphitic. In addition, the chemical environment of the electroactive material was disturbed because of the formation of the hydrogen-bridge bond and the redshift of the N-H bending. Consequently, these led to the low diffusion of electrolyte ions, high interfacial resistance, and electronic disorder in the electroactive material because of the collapse of the scaffold, inefficient diffusion of electrolyte ions, and an increase in the electron density that interfered with the electron transfer in the electroactive material

Performance stability of solid-state polypyrrole-reduced graphene oxide-modified carbon bundle fiber for supercapacitor application

The stability performance of a solid-state polypyrrole-reduced graphene oxide (PPy-rGO) supercapacitor electrode after a series of charging-discharging cycles is investigated. The electrochemical performances show that the capacity retention, specific capacitance, equivalent series resistance, and charge transfer resistance all decrease after charging-discharging cycles. Thermogravimetric analysis shows the degradation of electroactive materials, causing decreased electrochemical performance of PPy-rGO. The morphology changes reveal that the pore size is reduced by ∼12 μm at the 1000th charge-discharge cycle, which limits the diffusion of electrolyte ions into the electrode. The positive shifts in the binding energy of the N1s spectra at the 500th and 1000th charge-discharge cycles indicate the formation of a hydrogen-bridge bond, affecting the electron transfer in the PPy-rGO composite as observed through X-ray photoelectron spectroscopy. Moreover, the structural properties of rGO change from amorphous to graphitic after a series of charging-discharging processes, as shown by the Raman spectra. Furthermore, the peak of the NH bending vibration is red-shifted by approximately 108 cm−1, indicating the changes in the chemical environment after a series of charging-discharging cycles, as shown by Fourier transform infrared spectroscopy

Electrodeposition of Polypyrrole and Reduced Graphene Oxide onto Carbon Bundle Fibre as Electrode for Supercapacitor

Abstract A nanocomposite comprising of polypyrrole and reduced graphene oxide was electrodeposited onto a carbon bundle fibre (CBF) through a two-step approach (CBF/PPy-rGO-2). The CBF/PPy-rGO-2 had a highly porous structure compared to a nanocomposite of polypyrrole and reduced graphene oxide that was electrodeposited onto a CBF in a one-step approach (CBF/PPy-rGO), as observed through a field emission scanning electron microscope. An X-ray photoelectron spectroscopic analysis revealed the presence of hydrogen bond between the oxide functional groups of rGO and the amine groups of PPy in PPy-rGO-2 nanocomposite. The fabricated CBF/PPy-rGO-2 nanocomposite material was used as an electrode material in a symmetrical solid-state supercapacitor, and the device yielded a specific capacitance, energy density and power density of 96.16 F g− 1, 13.35 Wh kg− 1 and of 322.85 W kg− 1, respectively. Moreover, the CBF/PPy-rGO-2 showed the capacitance retention of 71% after 500 consecutive charge/discharge cycles at a current density of 1 A g− 1. The existence of a high degree of porosity in CBF/PPy-rGO-2 significantly improved the conductivity and facilitated the ionic penetration. The CBF/PPy-rGO-2-based symmetrical solid-state supercapacitor device demonstrated outstanding pliability because the cyclic voltammetric curves remained the same upon bending at various angles. Graphical Abstract Carbon bundle fibre modified with porous polypyrrole/reduced graphene oxide nanocomposite for flexible miniature solid-state supercapacitor