Graphene Supercapacitors

Prior to the use of graphene, a carbon-based material such as activated carbon was extensively used as an electrode material in the construction of supercapacitors due to its large surface area and low cost. However, in such stmctures, there are a lot of carbon atoms that cannot be accessed by the electrolyte ions, as illustrated in Fig. 4.11, and are effectively wasted consequently this is a major factor that limits the specific capacitance (which is F/g) of activated carbon electrodes. Additionally, it is reported that the low electrical conductivity of 

Carbon Specific surface area/m Density/g cm Electrical conduct vity/S cm Cost Aqueous electrolyte F F cm Organic electrolyte F g F cm  

Reproduced from Ref. [57] with permission from The Royal Society of Chemistry 

Other notable work [58] has used the approach shown in Fig. 4.12 where a specific capacitance value of 326 F g at 20 mV s was observed, which compared to 83 F g where CNTs were not used. 

These unique flexible supercapacitors have been shown to exhibit high stability and lose only 6 % of their electrical conductivity after being physically manipulated (bent) 1,000 times [59]. The high capacitance per geometric area is 81 mF cm which is equivalent to 120 F g of which 99 % of the capacitance is retained over 5,000 cycles. 

---

Chen, W., R. B. Rakhi, and H. N. Alshareef. 2013. Capacitance enhancement of polyaniline coated curved-graphene supercapacitors in a redox-active electrolyte. Nanoscale 5 4134-4138. 

Le LT, Ervin MH, Qiu H, Fuchs BE, Lee WY (2011) Graphene supercapacitor electrodes fabricated by inkjet printing and thermal reduction of graphene oxide. Electrochem Commun 13 355-358... 

G. Ning, Z. Fan, G. Wang, J. Gao, W. Qian, F. Wei, Gram-scale synthesis of nanomesh graphene with high surface area and its application in supercapacitor electrodes, Chemical Communications, 47 (2011) 5976. 

Electrostatic interactions have recently been exploited for the synthesis of gra-phene-CNT hybrids. For example, poly(ethyleneimine) (PEI) coated graphene has been mixed with acid treated CNTs in a layer-by-layer method to form high surface area electrodes for supercapacitors [90]. Furthermore, Lu et al. prepared a supercapacitor electrode by mixing PDDA coated CNT-Mn02 hybrid with RGO [91]. 

Li, Z., et al., Electrostatic layer-by-layer self-assembly multilayer films based on graphene and manganese dioxide sheets as novel electrode materials for supercapacitors. Journal of Materials Chemistry, 2011. 21(10) p. 3397-3403. 

Yu, D. and L. Dai, Self-assembled graphene/carbon nanotube hybrid films for supercapacitors. The Journal of Physical Chemistry Letters, 2009.1(2) p. 467-470. 

Lei, Z., F. Shi, and L. Lu, Incorporation of Mn02-coated carbon nanotubes between graphene sheets as supercapacitor electrode. ACS Applied Materials Interfaces, 2012. 4(2) p. 1058-1064. 

Niu, Z., et al., Electrophoretic build-up of alternately multilayered films and micropatterns based on graphene sheets and nanoparticles and their applications in flexible supercapacitors. Smaii, 2012. 8(20) p. 3201-3208. 

Dong, X., et al., Synthesis of a Mn02-graphene foam hybrid with controlled Mn02 particle shape and its use as a supercapacitor electrode. Carbon, 2012. 50(13) p. 4865-4870. 

Fig. 27 Supercapacitor study using graphene electrodes (5 mg each), (a) Cyclic voltammogram of chemical vapor deposited graphene (CG) nanodiamond derived graphene (NG) and exfoliated graphene (EG), (b) Evolution of specific capacitance vs scan rate. (Reprinted with permission Ifom [243])...

Yu A, Roes 1, Davies A et al (2010) Ultrathin, transparent, and flexible graphene films for supercapacitor application. Appl Phys Lett 96 253105... 

Vivekchand SRC, Rout CS, Subrahmanyam KS et al (2008) Graphene-based electrochemical supercapacitors. J Chem Sci 120 9-13... 

Fan, Z. et al.. Asymmetric supercapacitors based on graphene/MnOj and activated carbon nanofiber electrodes with high power and energy density. Adv. Funct. Mater. 2011,27(72 , 2366-2375. 

Zhu Y, MuraliS,StollerMD,GaneshKJ,CaiW,FeiTeiraPJ,Pirkle A, WallaceRM,Cychosz KA, Thommes M, Su D, Stach EA, Ruoff RS (2011) Carbon-based supercapacitors produced by activation of graphene. Science 332 1537-1541... 

---