The need for alternative energy sources has led to renewed research interests in electrochemical energy storage systems, especially supercapacitors [1]. Carbon materials such as carbon blacks, carbon fibres, cloths and nanotubes [2], have been used as electrode supports in supercapacitors. Carbon nanotubes (CNTs) have attracted attention due to their unique properties such as high surface area and high porosity that lead to high power densities of supercapacitors [2]. In the quest for an alternative sources, researchers have explored the charge storage properties of different metal oxide systems such as anhydrous Co-Ni oxides in alkaline medium, MnO₂ in neutral and acidic conditions, NiO in an acidic conditions [3], Co₃O₄ in an alkaline medium [4], and Fe₃O₄ in neutral solution (Na₂SO₄) and in both neutral and alkaline media [5], as an inexpensive alternatives to RuO₂. In addition to good supercapacitive behaviour, metal oxides also have the advantage that they can be readily made into thin films.

Although, supercapacitive properties of metal oxides on different substrates have been reported, this work represents the first time a comparative study of the supercapacitive properties of three metal (Ni, Fe, Co) oxide nanoparticles electrochemically deposited onto SWCNTs was carried out. In this work, Supercapacitive properties of single-walled carbon nanotubes/metal oxides nanocomposites (SWCNT-MO where M=Ni, Fe, Co) is described. The SWCNT-MO nanocomposites were confirmed with SEM, EDX and XPS techniques. Supercapacitive properties of the modified electrodes in H₂SO₄ and Na₂SO₄ electrolytes was investigated using cyclic voltammetry (CV), galvanostatic constant current charge-discharge (CD) and the electrochemical impedance spectroscopy (EIS) techniques. Electrodecorating acid-functionalised SWCNTs with metal (Ni, Fe, Co) oxide nanoparticles leads to significant enhancements on the supercapacitive properties of these materials in acidic and neutral media compared to many other literature reports. SWCNT-NiO nanocomposite modified electrodes gave better supercapacitive performance with a specific capacitance of 186 mFcm^-2 (or 928 Fg^-1). This value compared quite favourably and even higher than values hitherto reported in several literature.

References

1. M. Winter, R. J. Brodd, Chem. Rev. 2004, 104, 4245.

2. A. T. Chidembo, K. I. Ozoemena, B. O. Agboola, V. Gupta, G. G. Wildgoose, R. G. Compton, Energy Environ. Sci. 2010, 3, 228.

3. Q. Wang, Z. Wen, J. Li, Adv. Funct. Mater. 2006, 16, 2141.

4. L. Cao, M. Lu, H. L. Li, J. Electrochem. Soc. 2005, 152, A871.

5. S. Y. Wang, K. C. Ho, S. L. Kuo, N. L. Wu, J. Electrochem. Soc. 2006, 153, A75.