Preparation and performance of polyaniline–multiwall carbon nanotubes–titanium dioxide ternary composite electrode material for supercapacitors

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Abstract

Multi-walled carbon nanotubes (MWNTs), and titanium oxide (TiO2) were incorporated in polyaniline (PANI) to enhance the pseudocapacitance and cycle stability of PANI. PANI–MWNTs–TiO2, ternary composite was prepared by in-situ chemical polymerization of aniline in the presence of MWNTs and TiO2. Morphology analysis of ternary composite revealed the uniform covering of MWNTs by PANI nanofibers and TiO2 nanoparticles. The specific capacitance of PANI–MWNTs–TiO2 is 270 F g−1, much higher than that of MWNTs (30 F g−1) and PANI (210 F g−1) electrodes. PANI–MWNTs–TiO2 showed good rate capability with excellent cycling stability.

Introduction

Supercapacitors, offering excellent power density, long cycle life, short charge–discharge times, safety, and low maintenance costs, are emerging as one of the most principal and advanced electrochemical energy storage devices, alongside batteries and fuel cells. They find applications in hybrid electronic vehicles, space ship, portable electronics, fast acting short term power backup for UPS, digital camera, etc. [1], [2]. Electrical double layer (EDLCs) capacitors using carbon materials store energy by ion adsorption, whereas pseudocapacitors (PCs) use redox active materials (conducting polymers or transition metal oxides) to store energy by fast electrochemical redox reactions are the two types of supercapacitors, categorized on storage mechanism [3]. To combine the advantageous properties of both EDLCs (excellent cycle life) and PCs (high specific capacitance), the recent research was focused on the hybrid materials by combining EDLC and PC-based materials. This had outcome in the development of novel binary or ternary composites with improved properties [4], [5], [6], [7].

Carbon nanotubes (CNTs) are the smart electrode materials for their use in EDLCs, because of their large accessible surface area, high conductivity, and superior stability. However, the specific capacitance of pristine CNTs was very low (generally <100 F g−1) [7]. Thus by incorporating high capacitive PC material such as transition metal oxide or conducting polymers will result in a hybrid material with enhanced properties retaining the high cycling stability of CNTs and the high capacitance of PC materials. Binary composites of CNT with polyaniline (PANI) is frequently investigated, because of the attractive properties of PANI viz., cheapness and easy availability of raw materials, environmental stability, ease of synthesis, redox tunability, electrical conductivity, biocompatibility, and easy acid–base doping–dedoping process [8], [9], [10]. Recent reports show the enhanced properties for PANI–CNT composite materials regarding thermal, electrical, and mechanical properties for application in sensors, capacitors, electrochromic devices, fuel cells, etc. [11], [12], [13], [14]. To further develop the electrochemical properties of PANI–CNT, a ternary composite of PANI–CNT with transition metal oxides such as manganese dioxide [15], [16], [17], ruthenium oxide [18], tin dioxide [19], iron oxide [19] and titanium dioxide [19], [20], [21] have been tried out. Among transition metal oxides, recently TiO2 has attracted as a promising PC electroactive material because of its excellent properties of chemical stability, electrochemical activity, low cost, low toxicity, and eco-friendly [22]. In our previous reports, we have shown the improved properties of PANI by incorporation of TiO2 [22].

In the present work, we have made an attempt to prepare a ternary composite of PANI–MWNTs–TiO2 and used as electrode material for supercapacitor. The ternary composite, PANI–MWNTs–TiO2 was synthesized by an in-situ chemical polymerization method. The spectral, morphological, thermal and electrochemical characteristics of the material was discussed.

Section snippets

Materials

Aniline, ammonium persulfate (APS), and sulfuric acid (H2SO4) were purchased from Rankem, India. Multi-walled carbon nanotubes (MWNTs) and sodium lauryl sulfate (SLS) were purchased from Sigma–Aldrich, USA, and used as received. Aniline and solvents were distilled under reduced pressure and stored in a refrigerator before use.

Synthesis of PANI–MWNTs–TiO2 composite

0.19 g of SLS is dissolved in a 50 mL of 1 M H2SO4, then 20 mg of MWNTs, 20 mg of TiO2 and 1.0 mL of aniline were added and sonicated for 1 h to obtain a uniform dispersion. To

Results and discussion

The electrochemical performance of conducting polymer PANI was improved by incorporation of MWNTs and TiO2, wherein the monomer, aniline was polymerized by using ammonium persulfate as an oxidant via chemical oxidation polymerization pathway in the presence of MWNTs and TiO2. SLS was used as an emulsifying agent. The performance and properties of resulting ternary composite were compared with PANI and MWNTs. The schematic representation for the synthesis of PANI–MWNTs–TiO2 is given in Scheme 1.

Conclusions

The PANI–MWNTs–TiO2 ternary composite was synthesized via in-situ chemical polymerization method. The composite was characterized by FE-SEM, TGA, and XRD. FESEM results show that the PANI and TiO2 was uniformly coated on MWNT and the materials were bound together in a three-dimensional nanoporous network. These network structures of the PANI–MWNTs–TiO2 composite comprise large surface area that gives rise to the excellent energy density of the supercapacitor. The maximum specific capacitance of

Acknowledgments

SBS and PS are thankful to IICT for carrying out this work at IICT; SBS is thankful to UGC-New Delhi for providing Ph.D. research fellowship. The National Research Foundation of Korea Grant funded by the Korean Government (MEST) (NRF2016R1D1A1B03934229) and Hannam University research fund in 2017 supported this work.

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