Short communicationKOH modified graphene nanosheets for supercapacitor electrodes
Highlights
► Graphene nanosheets modified by KOH treatment were used as supercapacitor materials. ► Some oxygen-containing functional groups were introduced by KOH treatment. ► The KOH treatment led to the improved electrochemical performance of graphene nanosheets.
Introduction
In recent years, electrochemical supercapacitors (ECs) have drawn increasing attentions in the filed of electrochemical energy storage and conversion owing to their high power capability and long cycle-life [1], [2]. Generally, on the basis of the energy storage mechanism, supercapacitors establish capacitance via two ways. The capacitance owing to pure electrostatic charge accumulated at the electrode/electrolyte interface is called the electric double-layer capacitance (EDLC), while the capacitance due to a Faradaic process is named as pseudocapacitance. The capacitance and energy density both are strongly dependent of the electrode materials used in the supercapacitor, and so far activated carbons are mostly studied and have been commercially used in EDLC typed supercapacitor. However, there is an increasing demand for supercapacitors as power storage device with higher energy density. To satisfy this demand, it is crucial to explore new materials with large capacitance. There have been a lot of efforts to develop novel carbon based materials for supercapacitor such as carbon nanotubes [3], [4], [5], [6], carbon aerogels [7], [8] and mesoporous carbon [9], [10]. Although these carbon materials have shown good electrochemical performance as EDLC materials, their complicated preparation process and high costs restricted the practical uses in large scale [11].
Graphene nanosheets, as new type of carbon with two-dimensional nanostructure, have attracted escalating attention due to their unique properties such as the quantum hall effect at room temperature [12]. They are also considered as appealing candidate electrode materials in energy storage field due to their good electrical conductivity, low cost, excellent mechanical property and high specific surface area. Recently many reports demonstrated that graphene nanosheets [13], [14], [15], [16] and their composites such as MnO2/graphene [17], polyaniline/graphene [18], Ni(OH)2/graphene [19] possessed a high capacity as electrode materials in supercapacitor. Certain chemical modification of graphene nanosheets might help to further improve the electrochemical performance [20], [21]. Although the specific capacitance of the carbon materials can be greatly increased after activation with KOH [11], [22], the approach has not been reported on chemical activation of graphene nanosheets.
Here, we report the modification of the graphene nanosheets using concentrated KOH solution and their resulted electrochemical performance as supercapacitor electrode materials. The primary electrochemical experiments showed that the specific capacitance was greatly enhanced after such modification.
Section snippets
Materials and methods
All chemicals were of analytical grade and used without further purification. Double distilled de-ionized water was used for making all the solutions. In a typical experiment, 1.5 g graphene nanosheet powders (XG sciences) were added to 150 mL KOH (10 M) aqueous solution, ultrasonic for 3 h. Then the mixture solution was washed and filtered with distilled water until the pH of filtrate water became neutral. The filtered product was dried at 100 °C for 12 h.
Characterization
Fourier transform infrared (FT-IR) spectra
Results and discussion
Field-emission scanning electron microscope was used to examine the morphology of KOH modified graphene powders. The SEM images of both the pristine graphene powder and KOH modified graphene powders are shown in Fig. 1A and B, respectively. The pristine graphene powders are composed of aggregated sheets closely associated with each other as judged from the photos. After treated by KOH, the morphology showed no obvious changes compared with that of the pristine graphene, i.e., the treatment
Conclusion
We reported in this study the KOH modified graphene nanosheets and their performance as supercapacitor electrode materials. The edge defects and oxygen containing groups have been resulted in the treated graphene powders. The KOH treated graphene as electrode materials were characterized and tested, and yielded enhanced specific capacitance value over the untreated graphene. This method might provide a simple and more cost-effective route to improve the electrochemical performance of graphene
Acknowledgement
This work was supported by the grant of California EISG 55697A/07-21.
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