Free-standing graphene was first isolated from graphite by micromechanical exfoliation using scotch tapes in 2004. Reduced GO (rGO) is obtained by the extensive reduction of GO using different methods, yielding a significantly lower O content compared to GO. 1- 4 The most widely used derivative of graphene, graphene oxide (GO), is a chemically modified graphene material with abundant O-containing functionalities on its basal planes and edges, typically having lower C/O atomic ratios. The substantial π-electron conjugation in graphene results in fascinating electronic, thermal, magnetic, optical, mechanical, and chemical properties. Graphene, ideally, is a single-atom-thick sheet of sp 2-bonded carbon atoms arrayed in a hexagonal lattice. We hope this review stimulates more studies to realize the on-demand production of graphene materials with desired properties using electrochemical exfoliation methods.
Lastly, we propose our perspectives on further research. For all synthesis methods, we compare the properties of resulting graphene materials such as C/O ratios, lateral size, layer numbers, and quality characterized by Raman spectroscopy. Further, we summarize electrochemical exfoliation methods used to dope graphene materials, introduce covalent functional groups, incorporate various nanoparticles, and assembly of graphene architectures. Next, we survey synthesis methods for GO and examine how the pretreatment of the graphite electrodes, electrolytes, and operation parameters, such as applied voltages, electrolyte temperatures, and mechanical forces, affect the quality of GO. Thus, in this review, we first discuss synthesis methods for graphene materials with high C/O ratios from four aspects: graphite electrodes, equipment engineering, electrolytes, and additional reduction methods. The synthesis conditions for synthesizing pristine graphene, graphene oxide (GO), and graphene composites are significantly different. Graphene material synthesis methods generally have a trade-off between increasing production yield and achieving better material property control. This review examines research progress in the last 5 years, from 2015 to 2019. The electrochemical exfoliation of graphite has emerged as a simple method to produce graphene materials.
Synthesis of structurally controlled graphene materials is critical for realizing their practical applications.
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