Elsevier

Synthetic Metals

Volume 175, 1 July 2013, Pages 138-145
Synthetic Metals

Highly stable polypyrrole film prepared by unipolar pulse electro-polymerization method as electrode for electrochemical supercapacitor

https://doi.org/10.1016/j.synthmet.2013.05.013Get rights and content

Highlights

  • Superstable PPy thin film was fabricated using a facile UPEP method.

  • The growing PPy film was found to keep at an oxidized state during polymerization process.

  • Ordered structure with reduced chain defects of PPy film was obtained.

  • The PPy film exhibited an excellent cycling stability even in a neutral solution.

Abstract

Polypyrrole (PPy) film was fabricated on platinum substrate by a facile unipolar pulse electro-polymerization (UPEP) method. Mechanism for the formation of highly stable PPy film was proposed based on the chronoamperogram obtained during the polymerization process. Structure, surface morphology and hydrophilic property of the PPy film prepared using either UPEP method or potentiostatic method (PM) were characterized by Fourier transfer infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and contact angle goniometer, respectively. Electrochemical performances of PPy films prepared by UPEP and PM were compared using cyclic voltammetry (CV), galvanostatic charge/discharge tests and electrochemical impedance spectroscopy (EIS) in 1.0 M of KCl solution. It is found that the PPy film prepared by UPEP method under the conditions of ultra short on-time pulse (10 ms) and low temperature (10.0 °C) showed an ordered structure with reduced chain defects and exhibited high specific capacitance and excellent cycling stability in neutral solution. The capacitance of such a PPy film electrode retained 93.6% of its initial value even after 50,000 charge/discharge cycles. The specific capacitance of the UPEP PPy film reached 406.0 F g−1 at a scan rate of 5 mV s−1 when temperature, pulse potential, pulse time ratio (ton/toff) and pulse cycles were 10.0 °C, 0.7 V, 10 ms/100 ms and 12,000, respectively.

Introduction

Conducting polymer (CP) has attracted considerable attention for the development of electrochemical capacitor (EC) because of its high electrochemical activity, remarkable environmental stability and low cost [1], [2], [3]. Among the CPs, polypyrrole (PPy) was considered a particularly appropriate electrode material for EC due to its better electrochemical activity in neutral (pH  7) aqueous media and lower carcinogenic risk associated with its degradation product [4], [5].

However, similar to other CPs, PPy showed instability after long-term cyclical usage because the redox sites in its backbone were not sufficiently stable during the repeated redox processes [6], [7]. Recently, several strategies, such as compositing PPy with porous carbon materials [8], [9] and doping of various ions in its microstructure [10], [11], were applied to improve the electrochemical performance of PPy-based supercapacitor. It is found that the surface morphology and the intrinsic capacitive property of PPy material were significantly depended on the polymerization method and synthesis condition [12], [13], [14], [15]. Generally, PPy film can be synthesized either by chemical method or by electrochemical polymerization [16], [17]. In comparison with the chemical method, the electrochemical polymerization method, such as galvanostatic [18], potentiostatic [19] or cyclic voltammetric [20], [21] polymerization, was considered as a simpler and more attractive technique to obtain the PPy film adhered well on the anode. Furthermore, the film thickness could be tuned by controlling the total charge passed during the deposition process. Recently, pulse potentiostatic method (PPM) [22], [23], [24], [25], [26] and pulse galvanostatic method (PGM) [27], [28], [29], [30] were developed. The PPy film fabricated by PPM was found to have better electrical conductivity and more excellent level of molecular anisotropy [23]. Furthermore, its surface became smoother due to the application of the pulse mode. However, a part of the electrical input was simultaneously consumed for the reduction of PPy, resulting in lower coulombic efficiency. When the PPy film was fabricated on porous carbon materials, such as graphene [25] and carbon nanotube network [26], and applied for the supercapacitor by PPM, higher specific capacitance and higher energy density were obtained owing to the higher specific surface area of the conductive matrix. On the other hand, the PPy film prepared by PGM was found to have lower defect density in the polymer structure and higher doping degree with excellent electrochemical reversibility [28]. However, the corresponding oxidation potential of the film was found to be changed with time, and the PPy film could be over-oxidized at the higher pulse peak current during the polymerization process.

In our previous studies, a unipolar pulse electro-deposition method, which combines the advantages of PPM and PGM, was developed for the preparation of organic and inorganic composited electroactive materials [31], [32], [33]. In this technique, an on-time period, in which a potential is fixed and current can be generated, is applied, followed by an off-time period, in which no current is allowed to flow. Using this method, inorganic NiHCF film with controllable structure [31], nanorod polyaniline (PANI) film [32] and NiHCF/CS/CNTs composite film with high electrocatalytic activity were successfully fabricated [33]. In the present study, the PPy film with high specific capacitance and excellent cycling stability in neutral solution was also prepared on platinum substrate using this unipolar pulse method; here we called it unipolar pulse electro-polymerization (UPEP) method. Microstructure, hydrophilic property and electrochemical performance of the PPy film were characterized and compared with those films prepared by potentiostatic method (PM). In order to investigate the cycling stability of the film in neutral solution, 50,000 cycles of charge/discharge were performed.

Section snippets

Materials

Pyrrole (Sigma–Aldrich) was distilled under reduced pressure and stored in nitrogen atmosphere prior to use. Other chemicals were reagent grade and used without further purification. All solutions were prepared using ultra pure water (Millipore 18.2  cm).

Electrode preparation

Electrochemical preparation and characterization of the PPy film were performed using a three-electrode system in conjunction with a VMP3 Potentiostat (Princeton, USA) operated with a computer interface using a software EC-Lab for control and

Electro-polymerization process of PPy films

The optimum operation parameters for the electrochemical polymerization of PPy employing UPEP method was found to be 0.7 V, on-time of 10 ms and off-time of 100 ms over 12,000 cycles. Fig. 1A and B shows the first 0.3 s and the last 0.6 s current density/potential-time transient curves respectively during the pulse polymerization process for the fabrication of PPy film. As shown in Fig. 1A, the initial open circuit potential (OCP) on the working electrode was approximately 0.35 V and no current

Conclusions

Highly stable PPy film was successfully synthesized by using a facile UPEP method. UPEP PPy film exhibited an ordered structure with reduced chain defects. Such a structure improved the hydrophilicity and charge transfer rate of the film. EIS measurements indicated that the UPEP PPy film provided lower impedance than the PM PPy film. The PPy films prepared by UPEP method showed a specific capacitance as high as 406.0 F g−1 at a scan rate of 5 mV s−1 and an excellent cycling stability, with only

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (No. 21276173), Natural Science Foundation of Shanxi Province (No. 2012011020-5 and 2012011006-1), International Joint Research Project of Shanxi Province (No. 2011081028) and JSPS KAKENHI Grant Number 24651066.

References (50)

  • X.F. Lu et al.

    Progress in Polymer Science

    (2011)
  • G.A. Snook et al.

    Journal of Power Sources

    (2011)
  • B.C. Kim et al.

    Synthetic Metals

    (2011)
  • Y.K. Zhou et al.

    Electrochimica Acta

    (2004)
  • B. Muthulakshmi et al.

    Journal of Power Sources

    (2006)
  • M.N. Akieh et al.

    Synthetic Metals

    (2011)
  • B. Ding et al.

    Electrochimica Acta

    (2012)
  • B.C. Thompson et al.

    Biomaterials

    (2011)
  • I. Carrillo et al.

    Synthetic Metals

    (2012)
  • K. Fukami et al.

    Electrochemistry Communications

    (2008)
  • M. Wei et al.

    Synthetic Metals

    (2010)
  • K.F. Babu et al.

    Synthetic Metals

    (2009)
  • B.C. Kim et al.

    Journal of Power Sources

    (2008)
  • J.C. Vidal et al.

    Biosensors and Bioelectronics

    (1998)
  • P.A. Fiorito et al.

    Journal of Electroanalytical Chemistry

    (2005)
  • P.A. Fiorito et al.

    Talanta

    (2006)
  • H.H. Zhou et al.

    Synthetic Metals

    (2007)
  • M.S. Kiani et al.

    Polymer

    (1992)
  • H.F. Jiang et al.

    Electrochimica Acta

    (2010)
  • Y.P. Fang et al.

    Journal of Power Sources

    (2010)
  • R.K. Sharma et al.

    Electrochemistry Communications

    (2008)
  • J.P. Wang et al.

    Synthetic Metals

    (2010)
  • X. Li et al.

    Materials Letters

    (2012)
  • X.G. Hao et al.

    Thin Solid Films

    (2012)
  • Y. Li et al.

    Synthetic Metals

    (2012)
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