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Article http://pubs.acs.org/journal/acsodf
Efficient Graphene Production by Combined Bipolar Electrochemical Intercalation and High-Shear Exfoliation Emil Tveden Bjerglund,† Michael Ellevang Pagh Kristensen,†,⊥ Samantha Stambula,‡ Gianluigi A. Botton,‡,§,∥ Steen Uttrup Pedersen,*,† and Kim Daasbjerg*,† †
Carbon Dioxide Activation Center, Department of Chemistry and Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark ‡ Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada § Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L9S 4M1, Canada ∥ Canadian Centre for Electron Microscopy, McMaster University, Hamilton, Ontario L8S 4M1, Canada ⊥ Radisurf Aps, Arresøvej 5B, 8240 Risskov, Denmark S Supporting Information *
ABSTRACT: In this study, we demonstrate that bipolar electrochemistry is a viable strategy for “wireless” electrochemical intercalation of graphite flakes and further large-scale production of high-quality graphene suspensions. Expansion of the graphite layers leads to a dramatic 20-fold increase in the yield of high-shear exfoliation. Large graphite flakes, which do not produce graphene upon high shear if left untreated, are exfoliated in a yield of 16.0 ± 0.2%. Successful graphene production was confirmed by Raman spectroscopy and scanning transmission electron microscopy, showing that the graphene flakes are 0.4−1.5 μm in size with the majority of flakes consisting of 4−6 graphene layers. Moreover, a low intensity of the D peak relative to the G peak as expressed by the ID/IG ratio in Raman spectroscopy along with high-resolution transmission electron microscopy images reveals that the graphene sheets are essentially undamaged by the electrochemical intercalation. Some impurities reside on the graphene after the electrochemical treatment, presumably because of oxidative polymerization of the solvent, as suggested by electron energy loss spectroscopy and X-ray photoelectron spectroscopy. In general, the bipolar electrochemical exfoliation method provides a pathway for intercalation on a wider range of graphite substrates and enhances the efficiency of the exfoliation. This method could potentially be combined with simultaneous electrochemical functionalization to provide graphene specifically designed for a given composite on a larger scale.
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INTRODUCTION Following the first micromechanical cleavage of graphene from graphite,1 applications of this two-dimensional (2D) material have been proposed within diverse areas such as polymer composites,2,3 energy storage,4 and nanoelectronics.5,6 All these applications aim to utilize the exceptional mechanical7 and electronic1,8 properties of graphene. Development of economic and high-yield bulk graphene production methods have become crucial to enable the further progress toward these applications.9 Currently, several strategies exist for large-scale top-down production of graphene from graphite, including chemical exfoliation,10 electrochemical exfoliation,11−14 and liquid-phase exfoliation using ultrasound15 or high shear.16 The high-shear exfoliation method developed by Paton et al. produces oxygenfree graphene of good quality.16 Unfortunately, the yield is low (
