Elsevier

Electrochimica Acta

Volume 235, 1 May 2017, Pages 623-631
Electrochimica Acta

Polyethylenedioxythiophene and molybdenum disulfide nanocomposite electrodes for supercapacitor applications

https://doi.org/10.1016/j.electacta.2017.03.102Get rights and content

Highlights

  • MoS2-PEDOT nanocomposite electrode material was synthesized using polyanion ‘PSS’ and surfactant CTAB in an aqueous media.

  • The supercapacitor based on composite MoS2-PEDOT electrode revealed higher energy density than graphene composite electrodes.

  • The specific capacitance of 361 Farad/gram (F/g) was obtained for 1:2 weight ratio of MoS2 to the EDOT monomer in MoS2-PEDOT nanocomposite based electrodes.

Abstract

An innovative nanocomposite electrode was chemically synthesized using molybdenum disulphide (MoS2)- polyethylenedioxythiophene (PEDOT) to understand the charge mechanism in a symmetric supercapacitor. The MoS2-PEDOT nanocomposite was produced at various ratios of MoS2 to ethylenedioxythiophene (EDOT) in an aqueous medium of polyanions polystyrene sulfonate (PSS) and cetyltrimethylammonium bromide (CTAB) at controlled conditions. The morphology, crystallinity, and optical properties of MoS2-PEDOT nanocomposite materials were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, particle size analyzer, Raman spectroscopy, X-ray-diffraction, and transmission electron microscopy (TEM) techniques, respectively. The electrochemical properties of the supercapacitor were investigated using cyclic voltammetry, charging–discharging at constant current and electrochemical impedance spectroscopy (EIS) techniques. The specific capacitance, power and energy densities of the supercapacitor were estimated using cyclic voltammetry (CV), charging–discharging, Nyquist and Bode plots. The specific capacitance was estimated to be 361 Farad/gram (F/g) for the 1:2 weight ratio of MoS2 to the EDOT monomer in the MoS2-PEDOT nanocomposite based electrodes. Nevertheless, this study provides a fundamental aspect of synthesis of nanocomposite material for optimum attainment supercapacitive properties based on the MoS2-PEDOT nanocomposite electrode for practical energy storage applications.

Introduction

Electrochemical supercapacitors have become a new and revolutionized energy storage field due to their specific capacitance, charging-discharging characteristics, compactness, power density and energy density applications [1], [2]. The recent advancement has shown that 2D-nanomaterials such as metal dichalcogenide nanosheets of MoS2 or others could replace graphene as candidate for obtaining high energy based supercapacitor electrode material [3], [4], [5]. The 2D-dichalcogenide MoS2 reveals high specific capacity and cycle stability when used as anode in lithium ion battery [6]. The 2D-layered MoS2 shows double layer charge storage capacity, and provides excellent supercapacitive properties due to the large surface area [7], [8], [9]. MoS2 also displays pseudocapacitance properties similar to ruthenium dioxide (RuO2) due the +2 to +6 oxidation states of Mo in the structure [8], [10]. Various conducting polymers (polyaniline ‘PANI’, polypyrrole ‘PPY’, polyethenedioxythiophene (PEDOT) and polythiophene ‘PTh’) have been used for supercapacitor applications due to their superior redox properties, high electrical conductivity and environmental stability [11], [12], [13], [14], [15], [16]. PEDOT possesses fast redox reactions, charging-discharging characteristics and stable conducting polymer, and it is used as an electrode material in various electrolytic solutions for supercapacitor applications [17], [18].

However, conducting polymers also illustrate poor stability and recyclability due to the Ohmic polarization in several solvents for supercapacitors applications [19]. The stability and recyclability of conducting polymers has been resolved by formation of nanocomposite with RuO2, TiO2, carbon nanotubes, graphite, activated carbon, graphene, etc. [19], [20], [21], [22]. MoS2 composites with conducting polymer (CP) have also been used as an electrode for supercapacitor applications [23], [24], [25]. The PEDOT/MoS2 composite electrode materials are synthesized using exfoliation of MoS2 and in-situ polymerization technique, and applied for supercapacitor and lithium battery applications [26], [27]. The surface analysis of the MoS2-CP nanocomposites has shown high porosity and active surface area [28]. MoS2 is a hydrophobic material, and its immiscibility in water creates an issue for the successful synthesis of nanocomposites in aqueous media. We have exploited the surface chemistry by using CTAB as surfactant for the presence of MoS2 in the aqueous solution. The use of CTAB allowed MoS2 to disperse uniformly in the resulting EDOT based polymerizing solution. The EDOT was dissolved in the aqueous solution in presence of PSS polyanions. As demonstrated in this work, MoS2-PEDOT nanocomposite materials were successfully synthesized using modified MoS2 in aqueous media using surfactant. The simplistic synthesis, superior electrochemical redox properties and higher specific capacitance of electrode material are key in the foundation of practical supercapacitor applications for energy storage applications.

Section snippets

Synthesis of MoS2-PEDOT

The MoS2-PEDOT was obtained by chemical oxidative polymerization technique using the monomer ‘ethylenedioxythiophene (EDOT)’ dissolved in a solution of 1 M HCl containing 2 mg/ml of polystyrene sulfonate salt. The MoS2 was dispersed in water using surfactant CTAB before combining with dual oxidants containing a solution of 0.05 M ammonium peroxydisulfate [(NH4)2S2O8)] and 0.05 iron chloride (FeCl3) under controlled conditions. Fig. 1 shows 1:1 MoS2-PEDOT, 2:1 MoS2-PEDOT, and 1:2 MoS2-PEDOT,

Physical and Structural Characterization

The porous structure of MoS2-PEDOT nanocomposite is illustrated in SEM and TEM images. Fig. 2 shows SEM pictures of 1:2, 2:1 and 1:1 based MoS2-PEDOT nanocomposite samples. The SEM pictures show the platelet structure for MoS2, while the PEDOT has wrapped around the MoS2 similar to studies as shown in literature [26], [30]. The TEM pictures (Fig. 3a–c) depict that the PEDOT is wrapped with MoS2 structure similar to the obtained SEM images. However, TEM images also reveal the lattice structure

Conclusions

The MoS2-PEDOT nanocomposite was chemically synthesized by oxidative polymerization of ethylenedioxythiophene (EDOT) and MoS2 using PSS polyanions and surfactant CTAB under controlled conditions. The MoS2-PEDOT composite showed uniform structure with plate like MoS2 structure wrapped in PEDOT. The infrared spectrum was sensitive to Csingle bondH vibrations and showed shifts to identify the prominent changes in the polymer structure. The Raman study has shown the Cdouble bondC asymmetric stretching vibration due to

Acknowledgements

The authors are grateful to Dr. Ashok Kumar for allowing the authors using the laboratory facilities and Michael McCrory in assisting in XRD and Raman measurements. The authors are also grateful to NREC at USF for the providing various instruments for materials characterization. We are thankful to CERC at USF for particle size measurement.

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