Synthesis and electrochemical characterizations of amorphous manganese oxide and single walled carbon nanotube composites as supercapacitor electrode materials

https://doi.org/10.1016/j.elecom.2006.02.027Get rights and content

Abstract

Long cycle performance at a high charge–discharge current of 2 A/g for the amorphous MnO2 (a-MnO2) and single walled carbon nanotubes (SWNTs) composites have been studied for the first time. The a-MnO2 and SWNT composites have been successfully synthesized via a novel room temperature route starting with KMnO4, ethanol and commercial SWNTs. Homogeneity of the synthesized composites was established by electron microscopic studies. Electrochemical properties of the synthesized composites were elucidated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. All the composites with different SWNT loads showed excellent cycling capability, even at the high current of 2 A/g, with the MnO2:20 wt% SWNT composite showing the best combination of coloumbic efficiency of 75% and specific capacitance of 110 F/g after 750 cycles. However, the composite with 5 wt% SWNTs showed the highest specific capacitance during initial cycles.

Introduction

Development of metal oxide-carbon nanotube (CNT) composites have gained interest in recent years owing to their potential applications requiring both high energy and high power densities, which are much sought in present day portable electronics.

Various metal oxides, such as RuO2, Co3O4, NiO, Fe2O3, Ir2O3, SnO2, MnO2 etc., are being studied for the supercapacitor applications [1], [2], [3], [4], [5], [6], [7]. Manganese oxide is one of the most promising pseudocapacitor electrode materials with respect to both its specific capacitance and cost effectiveness. Similarly, various carbonaceous materials, such as CNTs, mesoporous carbon, carbon blacks, and activated carbons have been studied as electrodes for electrical double layer capacitors (EDLCs) [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19].

CNTs are interesting class of materials that find applications in variety of energy storage/conversion applications, such as lithium ion battery anodes, catalyst supports in direct methanol fuel cells and electrodes for the EDLC based supercapacitors [10], [11], [12]. The main criteria for the EDLC based supercapacitor electrodes is the large surface area which contributes to the formation of a double layer at the electrode–electrolyte interface. While various carbonaceous materials, such as activated carbon, disordered carbon, mesoporous carbon and CNTs are under close scrutiny for use as EDLC electrode materials [10], [11], [12], [13], [14], [15], composites involving, carbon or CNT and RuO2 or MnO2 oxides, have also been reported [20], [21], [22], [23]. Among them, all the above preliminary studies involving MnO2 and CNT composites focused on optimal composition of CNTs and their rate capability for few cycles, and showed promising. However, long cycle performance at a considerably higher charge–discharge current has not been reported so far. Obviously, long cycle and high rate stability of an energy storage system is a very important parameter for its applications and needs to be evaluated. In this paper, we employed a simple precipitation technique to prepare the homogeneous composites of MnO2:SWNTs at room temperature and investigated their electrochemical properties as a supercapacitor electrode material cycled at a high specific current. The long cycle performance of the MnO2:SWNT composites at a high current has therefore been reported for the first time.

Section snippets

Experimental

The MnO2:SWNT composites with different weight ratios of 5–40 wt% SWNTs were prepared by a simple precipitation technique developed in our lab [24]. Briefly, the starting materials for the preparation of MnO2 are KMnO4 and ethanol. Firstly, the KMnO4 was made a saturated solution in deionized water. The SWNTs were procured in purified form from Helix materials Inc. and used as received. According to their technical data sheet, the diameter distribution is <2 nm and length 0.5–40 μm and exist as

Results and discussion

Structural characterizations for the room temperature synthesized a-MnO2 have been done using TEM, X-ray diffraction (XRD) technique, X-ray photoelectron spectroscopy (XPS), BET surface area measurements and the details are presented elsewhere [24]. The X-ray diffraction studies revealed an amorphous structure for the as synthesized material. Since the oxidation state of Mn is very critical for the electrochemical performance of the system as an electrode, XPS studies was performed and the Mn

Conclusions

A simple method for forming a homogenous composite of a-MnO2 and SWNTs has been demonstrated and for the first time a long cycle performance study at a high current for the composites has been studied. TEM observations showed entangled SWNT homogeneously mixed with the MnO2 nanoclusters. The EIS measurements showed a decrease in resistance with respect to the increase of SWNT content in the composites. The cyclic voltammetric studies showed typical capacitive behavior for the pure MnO2, the

Acknowledgements

The authors gratefully acknowledge financial support from National Science Foundation under the NSF award number DMI-0457555 and Louisiana Board of Regents under the award number LEQSF(2005-08)-RD-B-05.

References (29)

  • Y.S. Yoon et al.

    J. Power Sources

    (2001)
  • B.E. Conway et al.

    J. Power Sources

    (1997)
  • C.C. Hu et al.

    J. Electroanal. Chem.

    (2001)
  • K.S. Ryu et al.

    J. Power Sources

    (2002)
  • H.Y. Liu et al.

    Carbon

    (2005)
  • E. Frackowiak et al.

    Carbon

    (2001)
  • H.Y. Lee et al.

    J. Solid State Chem.

    (1999)
  • J.P. Zheng et al.

    J. Electrochem. Soc.

    (1995)
  • K.C. Liu et al.

    J. Electrochem. Soc.

    (1996)
  • C. Lin et al.

    J. Electrochem. Soc.

    (1998)
  • H. Kim et al.

    J. Electrochem. Soc.

    (2003)
  • Y.U. Jeong et al.

    J. Electrochem. Soc.

    (2002)
  • A.S. Claye et al.

    J. Electrochem. Soc.

    (2000)
  • Z.L. Liu et al.

    Langmuir

    (2002)
  • Cited by (280)

    • Mn<inf>3</inf>O<inf>4</inf> based materials for electrochemical supercapacitors: Basic principles, charge storage mechanism, progress, and perspectives

      2022, Journal of Materials Science and Technology
      Citation Excerpt :

      Subramanian et al. [63] successfully deposited the composite of amorphous-MnO2/SWCNT for the first time using a simple novel room-temperature route using KMnO4. This composite exhibited a specific capacitance of 110 F/g at 2 A/g with 75% Columbia efficiency after 750 cycles [63]. Thereafter, this strategy was also used to improve the conductivity of Mn3O4 by various synthetic protocols like successive ionic layer adsorption and reaction (SILAR) [64], dip-casting [65], and electrophoretic deposition [66] and chemical deposition [67].

    View all citing articles on Scopus
    View full text