In-situ chemical oxidative polymerization of aniline monomer in the presence of cobalt molybdate for supercapacitor applications

https://doi.org/10.1016/j.jiec.2016.01.031Get rights and content

Highlights

  • CoMoO4/PANI was prepared by in-situ chemical oxidative polymerization method.

  • FE-SEM studies show the spherical shaped particles of PANI covered over the CoMoO4.

  • Specific capacitance of 246 F/g was achieved for composite material at 5 mV/s.

  • A maximum energy density of 33 Wh/kg was obtained for CoMoO4/PANI composite.

Abstract

A simple and green approach for the preparation of cobalt molybdate/polyaniline (CoMoO4/PANI) composite via in-situ polymerization method has been reported. The growth of PANI conductive layer on the surface of plate-like CoMoO4 nanostructures has been confirmed by XRD, FT-IR, Raman and FE-SEM techniques. The prepared CoMoO4/PANI composite delivered a maximum specific capacitance of 246 F/g at scan rate of 5 mV/s, whereas pristine PANI exhibits only 160 F/g which attributed to the synergic effect on the conducting network between CoMoO4 and PANI. The cyclic stability measurement revealed that above 80% of its initial capacitance is retained even after long cycles.

Introduction

In recent times, many efforts have been made by the researchers to develop for environmental friendly energy storage and conversion systems including batteries, fuel cells, capacitors, supercapacitors in the fast-growing markets [1], [2], [3]. Among them, supercapacitors, (also known as electrochemical capacitors or ultracapacitors) are important energy-storage devices that possess high energy density than dielectric capacitors and high power density than the rechargeable batteries [4], [5]. Electrochemical capacitors (ECs) are categorized as electrical double layer capacitors (EDLC) and redox pseudocapacitors according to the mechanism of energy storage. The former one is accumulated via physical charge separation at the electrode/electrolyte interface while the later one utilizes reversible redox reactions occurring at the electrode surface. Recently, materials such as activated carbon, carbon aerogel, CNTs, graphene, polyaniline (PANI), polypyrrole (Ppy), polythiophene (PT), poly(3,4-ethyelenedioxythiophene) (PEDOT), RuO2, MnO2, Fe2O3, V2O5, NiO, ZnO, are used as active electrode materials for supercapacitors [1], [6], [7], [8], [9]. In these electrode materials, energy can be stored based on electrical double layer capacitance mechanism for carbon based supercapacitors [1] and based on pseudocapacitive charge storage mechanism for transition metal oxide and conducting polymers. Among these pseudocapacitive electrode materials, RuO2 is one of the promising materials for the pseudocapacitors [10]. However, the high cost of ruthenium has greatly limited it to commercial energy storage applications. Therefore, researchers have made immense efforts to explore alternative and inexpensive electrode materials. Nowadays, metal molybdates constitute an important class of semiconducting materials widely used in catalysis, sensors, magnetic, photoluminescence, and energy storage devices [11], [12], [13], [14], [15], [16]. Especially, pseudocapacitive CoMoO4 was extensively investigated as an active electrode material due to its better electrochemical properties such as high capacitance and high rate capability [17]. Many researchers focused on the cobalt molybdate for supercapacitor applications. At first, Mai et al. [18] synthesized heterostructured MnMoO4–CoMoO4 nanowires by micro-emulsion method and studied their capacitance behavior. Heterostructured MnMoO4–CoMoO4 nanowires show a capacitance of 187.1 F/g and excellent cycling stability. Xia et al., [19] reported the one-pot hydrothermal synthesis of CoMoO4/reduced graphene oxide composite and with enhanced electrochemical properties for supercapacitors.

Conducting polymers are generally considered to be an ideal electrode material for flexible energy storage devices [20], [21], [22], [23]. Among them, PANI is a unique conducting polymer due to its environmentally friendly nature, facile synthesis, and promising optical, electrical, and electrochemical properties [24]. But it suffers from the poor electrochemical cyclic stability of PANI. To overcome this demerit, many researchers are focused to make composites with carbon based materials, and metal chalcogenides and metal oxides to enhance the electrochemical cyclic stability [25], [26]. More significantly, it is reported that some binary metal oxides acquires a much better electronic conductivity and higher electrochemical activity than single component metal oxide [27], [28]. In addition, it is well known that the rate capability of electrode materials is mainly determined by the kinetics of ion diffusion and electronic conductivity [29], [30], [31]. Nowadays, abundant researches focused on the metal molybdates due to their various important properties [32]. In order to enhance the electrochemical properties of PANI, researchers are focusing on incorporating the binary metal oxide into the PANI [33]. However, the development of PANI based materials with a simple, reliable synthetic method and improved electrochemical properties still remains a massive challenge. Only a few reports are available on the binary metal oxide based PANI composite for electrochemical supercapacitor applications. On the basis of this strategy, we have successfully synthesized CoMoO4/PANI for electrochemical supercapacitor applications. Briefly, in this article, CoMoO4/PANI was synthesized via in-situ chemical polymerization of aniline monomer in the presence of CoMoO4 nanostructures. The spherical shaped PANI was uniformly spread over CoMoO4 nanostructures. The synthesized CoMoO4/PANI composite based electrode material demonstrated a high specific capacitance, high energy density than the pristine PANI and also better long term cyclic stability, showing that the auspicious evidences for this synthesized CoMoO4/PANI material could be utilized for supercapacitor applications.

Section snippets

Materials and methods

Aniline monomer (C6H5NH2) was purchased from Junsei, Japan. Ammonium peroxodisulfate (APS—(NH4)2S2O8) was purchased from Kanto Chemicals Co., Inc., Japan. Carbon black, polyvinylidine difluoride (PVDF), sodium molybdate (Na2MoO4) were purchased from Sigma-Aldrich Ltd., South Korea. Cobalt chloride hexahydrate (CoCl2·6H2O), sulfuric acid (H2SO4), hydrochloric acid (HCl), methanol (CH3OH), and ethanol (C2H5OH) were procured from Daejung chemicals Ltd., South Korea. All chemicals used in this

Results and discussion

In this study, an in-situ chemical oxidative polymerization of aniline monomer was performed in the presence of sonochemically synthesized CoMoO4 nanostructures. Fig. 1, shows XRD pattern of PANI and CoMoO4/PANI composites. The presence of broad peaks at 20.3° and 25.3° corresponds to the planes (0 2 0) and (1 1 0), respectively, indicating the periodicity parallel and perpendicular characteristics of polymer chain and also no sharp peak was observed which suggests the semi crystalline nature and

Conclusions

In conclusion, CoMoO4/PANI composite was successfully synthesized by an in-situ chemical oxidative polymerization approach and successfully applied for supercapacitor applications. The structure, surface morphology, and electrochemical behavior of synthesized material were thoroughly investigated. A maximum specific capacitance of 245.9 F/g was achieved for CoMoO4/PANI composite material which is significantly higher than the pristine PANI (159.8 F/g). Also, higher value of energy density of

Acknowledgement

This work was supported by the National Research Foundation of Korea (NRF) funded by the Korea Government GRANT (2013R1A2A2A01068926).

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