Carbon onions are multi-layered carbon materials that receive less attention than their carbon cousins graphene and nanotubes. This may soon change.
Carbon based nanomaterials have been extensively theoretically examined, demonstrate and commercialized in the last decade due to their exceptional electronic and structural properties. Carbon onions (COs) are relatively new members of the carbon nanomaterials family that consist of multilayered spherical closed carbon shells concentrically arranged one inside the other, like the layer of an onion. They were discovered by Ugarte in 1992 1 and obtained via intense electron irradiation of carbon soot. Their typical size is ~5nm-10nm.
They are also referred to as carbon nano-onions (CNOs) or onion-like carbon (OLC), and can be prepared using different carbon precursors. 2 3
Properties
COs are not as widely studied as other carbon nanomaterials such as graphene and nanotubes but possess exceptional properties due to their O-D structure such as:
• high surface area
• high mechanical and electrochemical stability
• high conductivity
• easy dispersion compared to nanotubes and graphene
• exceptionally fast charge-discharge rates stemming from their non-porous structure
• improved electronic properties.
Figure 1: TEM image of carbon onion.
Synthesis
A number of different synthesis methods for carbon onions have been developed such as:
• Arc discharge 4
• Laser ablation 5
• Plasma method 6
• Chemical vapor deposition (CVD)
• High temperature annealing in vaccum 7
• Thermolysis.
Applications
COs are mainly investigated as conductive additives in lithium-ion battery (LIB) and supercapacitor electrodes, or as active material for supercapacitor electrodes for high-power applications and for low temperature devices using ionic liquid electrolytes in hydrogen storage. CO-ECs demonstrate more than ten times the power density of activated carbon. They have also been investigated as counter electrode materials in dye-synsitized solar cells.
Another main area of application is their use as solid lubricants with superior tribological properties (friction and wear reduction) in machining and semiconductor manufacturing. They have also been investigated for application in catalysts, sensors 8 and composites.9
References
1. Ugarte, D. Nature 1992, 359, 707–709. doi:10.1038/359707a0
2. V. L. Kuznetsov, A. L. Chuvilin, Y. V. Butenko, I. Y. Mal’kov, V. M. Titov, Chemical Physics Letters, 222 (1994) 343-348.
3. J.Cebik, J.K.McDonough, F.Peerally, R.Medrano, I. Neitzel, Y.Gogotsi, S. Osswald, Nanotechnology, 24 (2013) 205703.
4. Tomita S., Hikita M., Hayashi S., Yamamoto K. A New and Simple Method for Thin Graphitic Coating of Magnetic-Metal Nanoparticles. Chem Phys Lett. 2000, 316(5–6), 361–364.
5. Radhakrishnan G., Adams P.M., Bernstein L.S. Room Temperature Deposition of Carbon Nanomaterials by Excimer Laser Ablation. Thin Solid Films. 2006, 515(3), 1142–1146.
6. Cota-Sanchez G., Soucy G., Huczko A., Lange H. Induction Plasma Synthesis of Fullerenes and Nanotubes Using Carbon Black-Nickel Particles. Carbon. 2005, 43(15), 3153–3166.
7. Qiao Z.J., Li J.J., Zhao N.Q., Shi C.S., Nash P. Graphitization and Microstructure Transformation of Nanodiamond to Onionlike Carbon. Scr Mater. 2006, 54(2), 225–229.
8. http://www.h2sense.eu/
9. V.A.Popov. Metal matrix composites with non-agglomerated nanodiamond reinforcing particles. In: Xiaoying Wang (Ed.) “Nanocomposites: Synthesis, Characterization and Applications», Nova Science Publishers, New York, 2013, pp.369-401.
