**3. Applications of reduced graphene oxide aerogels**

combination of polymer chains and graphene oxide layers led to the mechanical strength of the material, whose structure was not fundamentally changed even after deformation by 60% (**Figure 7c**). Therefore, x-rGO aerogel exhibits 8.6 times higher compressive stress as

**Figure 9.** (a–c) SEM image of rGO aerogel, PI monolith, and rGO/PI nanocomposite, respectively. (d, e) Digital images show the high-level deformation of bend and torsion of rGO/PI nanocomposite. (f) Retention of maximum stress at 50%

The second cross-linking option is the use of sol-gel technology, which is the preparation of a sol followed by its conversion to a gel-colloid system consisting of a liquid dispersion medium enclosed in a spatial grid formed by the connected particles of the dispersed phase. For the first time to produce aerogels based on reduced graphene oxide, this technology was applied by Worsley et al. [26]. The authors proposed the use of polymerization of resorcinol and formaldehyde in the presence of sodium carbonate in an aqueous dispersion of graphene oxide. The obtained material showed an increased electrical conductivity (~102 S/m) compared to the

et al. also obtained an rGO aerogel with a high degree of nitrogen doping (5.8 atomic %), having

/g. Later Sui

reduced graphene oxide (~0.5 S/m), as well as a high specific surface area of 584 m<sup>2</sup>

compared with rGO aerogel (**Figure 7d**).

48 Graphene Oxide - Applications and Opportunities

strain and total loss during 2000 cycles. (g) Tensile σ-ε curve for the rGO/PI [30].

The first and the most developing direction of applications is the use of such aerogels as active electrode materials for supercapacitors. The supercapacitor is an electrochemical device for storage of electric energy on the surface of highly porous materials with an organic or inorganic electrolyte. At the heart of the work of supercapacitors, there are two processes—the formation of a double electrical layer at the material/electrolyte boundaries and electrochemical reactions on the surface of the electrode material, leading to the appearance of pseudocapacitance [32]. Both processes occur on the surface of the material during the charge/discharge of the device, so the energy capacitance of these devices is highly dependent on the surface area of the aerogels used. The combination of an electrically conductive three-dimensionally connected structure and good electrical conductivity of graphene-like materials makes them extremely attractive for this application. The high specific surface area of aerogels based on the reduced graphene oxide provides high capacity on a double electrical layer. To introduce a pseudocapacitive component, the aerogel surface is ordinarily decorated with transition metal oxides (Mn, V, etc.) capable of participating in redox reactions during charge/discharge of the device, making a significant contribution to the overall capacitance value [33–36]. Also interesting is the direction in the creation of flexible supercapacitors. In the framework of this direction, in addition to the reduced graphene oxide, various polymers are introduced into the aerogel, such as glucose [37], polyvinyl alcohol [25], polyaniline [38], etc.

The second, but not less interesting and intensively developing, direction is the use of aerogels based on reduced graphene oxide for rechargeable lithium-ion batteries. Graphene-like materials are the most widespread anode materials in commercial Li-ion batteries [39, 40]. The main role of rGO aerogel is to facilitate the multidimensional electronic transport routes and to reduce transport spaces between the electrode and the electrolyte. The consequence of this is an increase in the performance of the batteries and their cyclic stability. Sometimes, rGO aerogels containing metal, metal oxide, and metal sulfide are used as hybrid materials for the cathode of Li-ion batteries [41]. Similar structures containing Fe3 O4 [42, 43] and Fe<sup>2</sup> O3 [39] show promising capacities (900–1100 mA\*h\*g−1) with good cyclicality. SnO<sup>2</sup> is also used as an integral part of the FOG aerogel for this application [44]. Batteries with this material also show high performance (600–1200 mA\*h\*g−1) [45].

to develop simple methods for obtaining regular structures based on reduced graphene oxide, suitable for real use. Secondly, special attention needs to be given to a detailed study of the mechanisms of the structure formation of such materials, since at the moment many of the processes are only described, but not explained theoretically. Third, one of the main factors is the high cost of graphene-like materials, which means that efforts should be made to develop cheaper methods for the synthesis of GO and rGO. However, despite the fact that in the near future the researchers will have to solve a number of the problems described above, one can say unambiguously that materials based on graphene-like particles are among the most promising for revolutionary changes in technology, science, and the life of all mankind.

Graphene Oxide/Reduced Graphene Oxide Aerogels http://dx.doi.org/10.5772/intechopen.78987 51

This work was partially supported by Russian Foundation for Basic Research (project

The authors declare that the research was conducted in the absence of any commercial or

Semenov Institute of Chemical Physics of Russian Academy of Sciences, Moscow, Russia

[1] Zhang X, Sui Z, Xu B, Yue S, Luo Y, Zhan W, et al. Mechanically strong and highly conductive graphene aerogel and its use as electrodes for electrochemical power sources.

[2] Chen W, Yan L. In situ self-assembly of mild chemical reduction graphene for threedimensional architectures. Nanoscale. 2011;**3**:3132-3137. DOI: 10.1039/C1NR10355E [3] Wu ZS, Winter A, Chen L, Sun Y, Turchanin A, Feng X, et al. Three-dimensional nitrogen and boron co-doped graphene for high-performance all-solid-state supercapacitors.

Journal of Materials Chemistry. 2011;**21**:6494-6497. DOI: 10.1039/C1JM10239G

Advanced Materials. 2012;**24**:5130-5135. DOI: 10.1002/adma.201201948

financial relationships that could be construed as a potential conflict of interest.

Gudkov Maskim Vladimirovich\* and Valery Pavlovich Melnikov

\*Address all correspondence to: gudkovmv@gmail.com

**Acknowledgements**

**Conflict of interest**

**Author details**

**References**

16-29-06440).

Three-dimensional electroconductive structures of rGO aerogels are an excellent platform for creating electrochemical sensors, strain gauge sensor, and biosensors. Introduction to the structure of metals, oxides, and hydroxides of metals provides high sensitivity and electrochemical stability [46]. Ultraelastic aerogels based on rGO and carbon nanotubes were fabricated for use in a strain gauge sensor with adjustable voltage/pressure measurement [47]. The sensitivity is adjusted by changing the aerogel density. In the compression test, the measurement coefficient was 230 and 125% for deformations of 30 and 60%, respectively. The aerogel containing gold nanoparticles in its structure was used for the electrochemical determination of hydroquinone and o-dihydroxybenzene [48]. The detection limit is 1.5 × 10−8 M for hydroquinone and 3.3 × 10−9 M for o-dihydroxybenzene.

In the technique, actuators are transducers that convert an input signal (electrical, optical, mechanical, pneumatic, etc.) into an output signal (usually in motion) that acts on the control object. Devices of this type include electric motors; electric, pneumatic, or hydraulic actuators; relay devices; comb drives; DMD mirrors; electroactive polymers; robotic grasping mechanisms, drives for their moving parts, including solenoid actuators and voice coils; and many others. Recently, the actuators have been intensively studied as potential devices in flexible displays, soft robotics, and haptic devices. rGO-based aerogels are ideal candidates for such devices, because they have high porosity, are ultra-light, flexible, and resilient. To be able to act on the aerogel with magnetic forces, magnetic nanoparticles of Fe3 O4 were introduced into it [49]. This material demonstrated great magnetic field-induced actuations of 52 and 35% along the radial and axial directions, respectively. Also, several works on actuators based on materials with shape memory are known. Li et al. developed an actuator based on an aerogel from rGO and trans-1,4-polyisoprene, which showed a strain of 80% at 10 V [31].
