**3. Colloidal graphene**

A colloidal solution of graphene (**Figure 1**) has graphene nanoparticles evenly distributed throughout the solution. In the colloidal solution of graphene the graphene nanoparticles remain dispersed in the solution without settling to the bottom, for quite a long time. Further, The colloidal solution of graphene has very large surface area and exhibits high electrochemical behavior. Further, the advantage of using solution phase to form various graphene devices such as sensors, electrodes, energy storage devices makes it more prominent method as compared

**35**

*Recent Progress in the Electrochemical Exfoliation of Colloidal Graphene: A Review*

to other synthesis methods of graphene such as chemical vapor deposition, liquid phase exfoliation, mechanical exfoliation method, epitaxy and hummer's method. Due to large surface area of colloidal dispersion of graphene, it has been suitably

The colloidal graphene has high specific surface area and does not exhibit aggregation. The colloidal graphene was produced by the intercalation of the sulfate ions in between the individual graphene nanosheets present in the graphite rod. This intercalation process separates the individual graphene nanosheets which accumulate in the electrolyte solution at the end of electrochemical exfoliation process to form the colloidal solution of graphene [14]. Various steps involved in the formation of colloidal solution of graphene through electrochemical exfoliation process are

The quality of colloidal graphene produced by the electrochemical exfoliation depends upon the type of the aqueous electrolyte used. Therefore, to improve the quality of colloidal graphene various electrolytes have been studied by researchers [8]. Some of the electrolytes used to prepare colloidal solution of graphene are ammonium sulfate, phosphoric acid, potassium sulfate, sodium sulfate, sulfuric acid electrolytes. In addition of these aqueous electrolytes lithium sulfate has also been observed to produce colloidal solution of graphene via electrochemical route [16]. The electrochemical exfoliation of graphene is performed by using one graphite rod and one platinum wire immersed in any aqueous solution containing sulfate ions. A DC voltage source is used for the exfoliation process [8]. Usually, a DC voltage of 10 V is applied for 1 to 1.5 hour for the exfoliation of graphene to complete. After 1.5 hour, the colloidal solution of graphene is obtained in the aqueous electrolyte solution (**Figure 3**). When the exfoliation process is completed, the graphite rod has been completely converted into graphene colloids in the solution. Later, the colloidal solution of graphene is used for the preparation of the graphene based electrodes.

utilized for the preparation of flexible energy storage devices [12–15].

**4. Electrochemical exfoliation**

*Colloidal solution of graphene in aqueous electrolyte.*

shown in **Figure 2**.

**Figure 1.**

*DOI: http://dx.doi.org/10.5772/intechopen.95522*

*Recent Progress in the Electrochemical Exfoliation of Colloidal Graphene: A Review DOI: http://dx.doi.org/10.5772/intechopen.95522*

**Figure 1.** *Colloidal solution of graphene in aqueous electrolyte.*

*Colloids - Types, Preparation and Applications*

of graphene sheets.

**2. Limitations of graphene synthesis methods**

the colloidal solution form so that it will be easy to fabricate these graphene based flexible electronics devices using spray coating, brush coating, screen printing techniques [8]. Therefore, it is absolutely necessary to produce the colloidal solution of graphene.

Various methods have been used for the preparation of graphene each having its own limitations as compared to others. Some of the prominent methods are mechanical exfoliation, Hummer's method, liquid phase exfoliation, epitaxial growth, chemical vapor deposition etc. First, the mechanical exfoliation method by which the graphene was first exfoliated from solid graphite source is a very time consuming technique of producing graphene from graphite [1]. It is a hit and trial method in which the researcher is not sure whether the graphene exfoliated on the scotch tape is single layered or multi layered graphene sheet. So, it is not a controllable and leads to a lot of wastage of time. Similarly the hummer's method uses very harmful acids and is also very time consuming method. The quality of graphene obtained from this method is not of high quality as indicated from the TEM results

Chemical vapor deposition requires very expensive and sophisticated equipment, hence the synthesis cannot be performed in all the laboratories [9, 10]. Liquid phase exfoliation is a technique where long hours of sonication process is required which is very time consuming process [11]. Further the long hours of sonication deteriorates the quality and size of graphene nanosheets in the dispersion. Therefore, among other methods of graphene synthesis it is found that the colloidal dispersion of graphene prepared by electrochemical exfoliation is time saving method, economical and easy to use in any laboratory without any sophisticated and expensive equipment. The relative advantages of electrochemical exfoliation

A colloidal solution of graphene (**Figure 1**) has graphene nanoparticles evenly

distributed throughout the solution. In the colloidal solution of graphene the graphene nanoparticles remain dispersed in the solution without settling to the bottom, for quite a long time. Further, The colloidal solution of graphene has very large surface area and exhibits high electrochemical behavior. Further, the advantage of using solution phase to form various graphene devices such as sensors, electrodes, energy storage devices makes it more prominent method as compared

method in comparison to others methods is shown in **Table 1**.

*Relative advantages of electrochemical exfoliation method in comparison to others.*

**S.No. Graphene synthesis method Relative advantage/disadvantage**

 Liquid phase exfoliation Requires Long hours of sonication, Time consuming Epitaxial growth Low yield, Difficult in graphene layer transfer Chemical vapor deposition Requires expensive and sophisticated equipment Mechanical exfoliation Not suitable for large scale production of graphene Hummer's method Harmful chemicals, acids used, graphene not pure Electrochemical exfoliation FASTER, HIGH YIELD, ENVIRONMENT FRIENDLY

**34**

**Table 1.**

**3. Colloidal graphene**

to other synthesis methods of graphene such as chemical vapor deposition, liquid phase exfoliation, mechanical exfoliation method, epitaxy and hummer's method. Due to large surface area of colloidal dispersion of graphene, it has been suitably utilized for the preparation of flexible energy storage devices [12–15].
