In another study, Zhao et al. [47]

In another study, Zhao et al. [47] used an electrochemical method for the synthesizes of graphene/WO3 nanocomposite. To synthesize the nanocomposite, 2 graphite rods, as both electrodes, were utilized and placed in the electrolyte with a distance of 4.0 cm. Twelve tungsten phosphate (H3PW12O40.xH2O) and sodium tungstate dihydrate (Na2WO4.2H2O) solution (1.0 g in 40 ml water) were electrolytes and employed respectively. As a result of the electrochemical method, WO3 nanorods on the surface of graphene were dispersed after applying 10 V DC to the electrolyte. Once the current was applied to the solution, positively charged graphite rod (anode) started to be corroded and after 30 min black precipitates deposited at the bottom of electrolyte. As a final step, the Na2S2O4 was added every half an hour and finally, the product was heated at 60 °C for 6 h. Fig. 5 provides the TEM image and XRD patterns of graphene and graphene/WO3 nanocomposite. TEM image of graphene/WO3 nanocomposite approved the proper dispersion of the WO3 nanorods on the surface of graphene sheets (Fig. 5a). Besides, the XRD patterns from graphene-based composite, despite simple graphene displayed diffraction peaks due to the presence of the WO3 crystalline nanoparticles (Fig. 5b).Fig. 5Download : Download high-res image (363KB)Download : Download full-size imageFig. 5. (a) TEM image of graphene sheets decorated with WO3 nanoparticles, and (b) the XRD patterns of graphene sheets decorated with WO3 nanoparticles and graphene prepared by electrochemical method, reproduced from [47].In a study by Kotkin et al. [48], an electrochemical method assisted by plasma was carried out for the exfoliation and decoration of cobalt on the surface of graphene. The used electrolyte was prepared by mixing the 1 M Na2SO4 and 0.01 M CoSO4 solution. The graphite electrodes were used as both anode and cathode materials. The alternating voltage of -150 V (cathodic) and +300 V (anodic) was applied for 10 h. In the anodic mode of process, the deposition of cobalt on the surface of cathode occurs. After that, the graphene/cobalt oxide composites are formed by cathodic type process; the deposited cobalt particles are dissolved in this condition.3.2. Functionalization of graphene with other nanoparticlesIn this section, the application of the electrochemical method for the synthesis of nanocomposites of graphene with other types of nanoparticles is reviewed. A single-stage simultaneous electrochemical exfoliation and decoration of graphene with metal nanostructures process was reported by Ejigu et al. [49]. The mixture of organic solvents of dimethyl carbonate (DMC), and ethylene carbonate (EC) was used as the electrolyte in their work. Then, the LiClO4 and tetraethylammonium tetrafluoroborate (TEABF4) with 0.1 M concentration was added in the mentioned organic solvents. For functionalization of the electrochemically exfoliated graphene with Au and Co, 0.15 mM of NaAuCl4 and Co(NO3)2 were added to the mentioned electrolytes, respectively. A graphite foil tape as a working electrode (pre-expanded by immersing in liquid nitrogen for 30 s followed by transferring into absolute ethanol), a Pt mesh as a counter electrode, and an Ag wire quasi-reference electrode was used for the electrochemical measurements. The electrochemical exfoliation testament was carried out by applying the anodic voltage of 4 V for 12 h under N2 atmosphere. Fig. 6 depicts the SEM images of the functionalized graphene with Au and Co with different magnifications prepared by the electrochemical method. Fig. 6a–c indicate the SEM images with different magnifications of the graphene/ Au composites. As can be seen, different forms of Au nanoparticles including the dendrites, lamellar, and whiskers have been decorated on the surface of graphene sheets. Fig. 6d depicts the SEM image of graphene/ Co composites, indicating the presence of small tips of Co nanoparticles on the surface of electrochemically exfoliated graphene.