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4. Experimental Section Electrochemical exfoliation of graphite. A graphite rod (Mersen, 99.995 % purity, 3.05 mm diameter) was used as working electrode connected to the anode for electrochemical exfoliation. A platinum mesh was used as counter- electrode (cathode) and placed parallel to the anode at a distance of around 2 cm. An aqueous solution of ammonium sulphate (Alfa-Aesar) with a concentration of 0.2 M was used as electrolyte. The electrochemical exfoliation process was carried out by applying a preliminary DC voltage of 2 V for 2 min in order to wet the graphite electrode, as recommended by Ambrosi and Pumera. [8d] Then, a positive DC voltage of 10 V was applied to the graphite electrode using DC power (Promax, DC-405) for the time required to attain the complete exfoliation of the graphite rod (∼ 2 h). This process was carried out under stirring, taking care to keep the reaction temperature within the 20-30oC range. The expanded graphite particles (EG) detached from the rod during the electrochemical exfoliation were collected by filtration and washed with abundant DI water. Immediately after the washing step, the EG sample was dispersed in water by sonication at high power (Sonics, Ultrasonic Vivracell, 750 W, 40 %) for 1.5 h. Afterwards, the sample dispersed in water was centrifuged at a speed of 3000 rpm (4300g) for 15 min to obtain a precipitated solid (REG) and a supernatant dispersion. The aqueous dispersion was formed by oxidized graphene (OG) sheets in concentrations of ∼ 2-3 mg/mL. Figure S1 shows the experimental setup employed in these experiments. Processable graphene dispersion. In a typical preparation of an aqueous graphene colloidal dispersion (ROG), 120 mL of OG dispersion (0.5 mg/mL) was mixed with 0.24 mL hydrazine (35 wt.% in water, Aldrich) and 0.42 mL 17PDF Image | Graphene from Electrochemically Exfoliated Graphite
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