Electrochemically exfoliated high-yield graphene in ambient temperature molten salts and its application for flexible solid-state supercapacitors

Electrochemical exfoliation of graphite has emerged as a potentially scalable approach to prepare graphene. However, most of exfoliated graphite particles are inhomogeneous and multilayer stacked structures including tens of layers thick graphite exist inevitably, thus the yield of few-layer graphene remains limited. In this study, we here propose a high-yield, scalable electrochemical exfoliation method in a ternary deep eutectic melts containing acetamide, urea and ammonium nitrate, where high viscosity, higher anionic intercalation potential and low migration speed can bring anions with solvents could co-intercalated into graphite uniformly, expand the interlayer of graphite gallery and then form steady graphite intercalation compounds, affording to complete sufficient intercalation. Finally decomposition of the intercalant facilitates expanded graphite to be exfoliated into graphene. Consequently, the yield is improved to 76% and the product primarily consists of 1-5 layer graphene, which exhibits a specific surface area (878 m(2) g(-1)) close to the theoretical value of three-layer graphene. Furthermore, all-solidstate flexible supercapacitors based on the graphene deliver a high area capacitance of 120 mF cm(-2), excellent mechanical flexibility and cycling stability (97.2% retention after 10000 cycles). This approach offers the potential for cost-effective, environmentally friendly and large-scale production of graphene and numerous advanced applications. (C) 2017 Elsevier Ltd. All rights reserved.