Preparation of High-quality Graphene via Electrochemical Exfoliation in Acidic Electrolytes: A Review
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Preparation of High-quality Graphene via Electrochemical Exfoliation in Acidic Electrolytes: A Review
Youning Gong1 and Chunxu Pan1 1 School of Physics and Technology, Wuhan University, Wuhan 430072, China ABSTRACT Since the discovery of graphene in 2004, graphene has already been one of the researching hotspots in the material science. As a promising method, electrochemical exfoliation has drawn great attention for producing graphene on industrial scale with high efficiency, low cost, and non-pollution. However, like other wet-chemical methods, the induced oxidation and chemical functionalization are unavoidable during the exfoliation process. Several solutions have been reported to overcome this issue and improve the graphene quality. In this review, we summarize the recent progress in preparation and potential applications of high-quality graphene via electrochemical exfoliation in acidic electrolytes, focusing on the technological innovation and related properties of obtained high-quality graphene. INTRODUCTION As a 2-D material made up of sp2-hybridized carbon atoms, graphene has drawn great attention for materials researchers, due to its remarkable optical, mechanical, electronic and thermal properties [1]. However, the limited scalability and extreme high cost for graphene preparation have limited its practical applications into everyday life products. Among various preparation methods such as mechanical exfoliation, epitaxial growth, chemical exfoliation and chemical vapor deposition (CVD), electrochemical exfoliation may present feasible alternatives for producing graphene on an industrial scale. Involving the use of electrolytes and an electrical current or voltage, the graphite working electrode is driven to corrode into graphene sheets by anodic oxidation or cathodic reduction [2]. Compared to cationic intercalation, anionic intercalation (mainly in aqueous electrolytes) is more effective and less time-consuming, which has almost predominated the recent works on the electrochemical exfoliation of graphite [3]. Like other liquid-phase exfoliation approaches, the successful electrochemical exfoliation mainly relies on the choices of proper electrolytes. The electrolyte plays a key role in the exfoliation process as it provides ions for the graphite intercalation and separation, as well as dissolves the obtained graphene sheets and restricts the agglomeration [4]. Sulfuric acid is the most widely used electrolyte for the interlayer spacing of graphite (0.335 nm) is slightly smaller to the size of sulfate ion (0.46 nm), which is favorable for the intercalation of sulfate ions [5]. What’s more, sulfate ions can also serve as the surfactant to reduce the
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re-stacking of graphene sheets in aqueous solution. Nevertheless, the induced oxidation and chemical functionalization are unavoid
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