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104 A. Petrovski et al. of methods for its production and application in many different fields of modern life. There are several well-developed methods for graphene production such as mechanical exfoliation, among them chemical vapor deposition (CVD), chemical exfoliation, liquid phase exfoliation of graphite or thermal decomposition of SiC etc. [6]. Particular attention was paid to the development of methods for production of high quality graphene (monolayerd or few layers only) with increased production yield and low production costs. Electrochemical approaches are a suitable alterna- tive for a high-yield production of graphene since electrolysis is simple, environ- mentally friendly, economic (taking place at ambient conditions) and flexible (the thickness can be controlled by potential or current adjusting). From the electrode reaction’s point of view, there are two basic approaches to produce graphene: (i) anodic oxidation of graphite to produce graphene oxide (GO) and further cathodic reduction to graphene and (ii) direct cathodic reduction to for produce non-oxidized graphene [7–9]. From the electrolyte’s point of view the electrochem- ical procedures can be divided in electrolysis in (i) aqueous and (ii) non-aqueous solutions. The mostly used aqueous electrolytes are sulfuric [10] and perchloric acids [11]. Non-aqueous electrolytes used for the electrochemical production of graphene are organic solvents, ionic liquids or molten salts. Ionic liquids have the added advantage of being non-volatile; they are also biodegradable [12]. The aim of this work is to produce graphene using a reverse potential in a sulfuric acid electrolyte. 11.2 Experimental Electrolytic exfoliation of highly-oriented graphite electrodes in an aqueous electrolyte with reverse change of the voltage between anode and cathode was performed in order to produce graphene. The electrochemical setup is schemati- cally shown in Fig. 11.1. As electrodes, two types of commercial graphite were used (M1 and M2). The reverse voltage was changed from +15 V to 15 V. Before the electrolysis, all electrodes were pretreated at constant reverse voltages of +5 V to 5 V for 5 min. The electrolytes used were (i) pure sulfuric acid (pH 1⁄4 0.5), (ii) sulfuric acid with KOH (pH1⁄41.2) and (iii) sulfuric acid with NaOH (pH1⁄41.2), prepared using chemicals of high purity. During the electrolysis, as a result of exfoliation of graphite electrode, sheets of graphene are suspended into the electrolytic solution. After electrolysis, the solu- tions were filtered through vacuum-filter; thereafter, the fine graphene sheets were washed several times with distillated water. The studied graphene samples were observed by scanning electron microscopy (JEOL 6390) and transmission electron microscopy (FEI Tecnai G2 Spirit TWIN equipped with LaB6). Structural characterisation as well as an estimation of the crystallite size and the number of layers were performed by Raman spectroscopy (micro-Raman multichannel spectrometer Horiba JobinYvon LabRam 300 Infinity). pericap@tmf.ukim.edu.mkPDF Image | Graphene Produced by Electrolysis
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