Among various methods to produce graphene sheets, electrochemical exfoliation has been regarded as an effective method for the mass production of high-quality graphene sheets because of its simplicity and environmental friendliness. However, conventional electrochemical exfoliation has a disadvantage of accumulating intercalating ions at graphite interlayers owing to the use of a constant voltage. In this study, we developed a DC switching technique to achieve more efficient intercalation of ions than that in the conventional method. In the DC switching method, positive and negative voltages are successively applied to release the accumulated intercalating ions. By testing various conditions, we found the optimum switching time to produce high-quality graphene sheets with the highest yield rate and the highest electrical conductivity. As a result, the graphene sheets using this DC switching technique showed 85% higher yield rate, 193% higher electrical conductivity, 160% larger area, and 25% thinner thickness than those obtained when using a constant DC method. We believe that this DC switching technique can be used for large-scale production of high-quality graphene sheets.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Electrochemical exfoliation of graphite
        2.3 Measurement of yield rate and preparation of graphene film
        2.4 Characterization of graphene sheets
    3 Results and discussion
        3.1 Yield rate of electrochemically exfoliated graphene
        3.2 Electrical conductivity and contact angle of electrochemically exfoliated graphene
        3.3 Morphology analysis of electrochemically exfoliated graphene
        3.4 Raman and XPS analyses of electrochemically exfoliated graphene
    4 Conclusions
    Acknowledgements 
    References

• Sungmook Lim(School of Mechanical Engineering, Chonnam National University)
• Jong Hun Han(School of Chemical Engineering, Chonnam National University)
• Hyun Wook Kang(School of Mechanical Engineering, Chonnam National University)
• Jea Uk Lee(Carbon Industry Frontier Research Center, Korea Research Institute of Chemical Technology (KRICT))
• Wonoh Lee(School of Mechanical Engineering, Chonnam National University)