Few-layer graphene via electrochemically cathodic exfoliation for micro-supercapacitors
(2.Great Scientific Research Institute, Datong Coal Mine Group Co., Ltd., Datong, Shanxi, China 037003)
【Abstract】The use of graphite as a raw material for efficient, green, and low-cost preparation of few-layer graphene is of great significance for the large-scale production and application of graphene. However, the efficient exfoliation of graphite to graphene without use of strong oxidants and acids is still a great challenge. Herein, we developed a green and scalable aqueous-based electrochemical cathodic exfoliation approach, in which graphite as a negative electrode can be electrochemically charged and expanded in an electrolyte of 6 mol·L−1 potassium hydroxide (KOH under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The obtained few-layer graphene has low oxygen content [1.27% (mass)], few defects (ID/IG < 0.035), a plate size of 5–10 μm, high conductivity of >200 S·cm−1, and good solution additivity. Moreover, such electrochemically exfoliated graphene (EG) nanosheets are readily used to produce highly solution-processable ink (1 mg·mL−1) in ethanol without the need of any surfactants, allowing for the production of large-area EG microelectrodes for EG based micro-supercapacitors (EG-MSCs). Furthermore, the as-fabricated aqueous EG-MSCs show ultrahigh scan rate of 100 000 mV·s−1 and short time constant of only 24 ms. More importantly, using ionic liquids-based electrolyte of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide with bis(trifluoromethanesulfonyl)imide lithium sal (EMIMTFSI/LiTFSI), EG-MSCs can work at a high voltage of 4.0 V, and show high volumetric energy density of 113 mW·h·cm−3, outperforming the most reported MSCs (< 50 mW·h·cm−3).
【Keywords】 electrochemical; cathode exfoliation; graphene; graphite; micro-supercapacitors;
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