Influence of medium on structure, morphology and electrochemical properties of polydiphenylamine/vanadium pentoxide composite

Date: Feb 25, 2019

Abstract

A facile, one-pot oxidative polymerization approach was used to synthesize polydiphenylamine (PDPA) and polydiphenylamine/vanadium pentoxide (PDPA/V₂O₅) composite using APS as an oxidizing agent. The reactions were carried out in two different reaction media (i.e. aqueous and acidic). The influence of these two mediums on molecular structure, morphology and thermal stability was investigated using FTIR spectroscopy, X-ray diffraction, SEM–EDS and thermogravimetric analysis. The temperature dependent electrical conductivity and dielectric properties (dielectric loss and dielectric constant) of these materials were also conducted. These studies revealed that in aqueous medium PDPA/V₂O₅ composite has formed however, in acidic medium only the PDPA polymer formed, suggesting different nature of V₂O₅ in these two medium. The results also showed that the PDPA/V₂O₅ composite has higher yield, good electrical conductivity, charge transport, dielectric losses and thermal properties as compared to that of PDPA. Furthermore, the electrochemical properties were evaluated by cyclic voltammetry, and electrochemical impedance spectroscopy and found that PDPA/V₂O₅composite shows good electrochemical properties.

Keywords

Polydiphenylamine Vanadium pentoxide Reaction medium Electrochemical properties 

1 Introduction

Continuous efforts for the development of strategic materials with controlled structure and property relationship have suggested a new direction for the formulation of polymer–metal oxide composites, with versatile properties. These polymer–metal oxide composites have wide applications in the field of energy storage, solar cell, batteries and supercapacitors [1, 2, 3]. These materials came to the new track, especially after the discovery of conducting polymers (CPs). CPs possess unique optical property, high electrical conductivity, good thermal and environmental stabilities, and inherent microporosity [4]. CP have versatile applications in the field of supercapacitors, batteries, solar cells, corrosion guards etc. [5, 6, 7]. However, it has been observed that CPs alone have failed to provide high conductivity and value added properties. Thus, to overcome these drawbacks researchers have moved towards the synthesis of their copolymers and composites by incorporating metal oxide into the CP matrix. Various metal oxides such as nickel oxide, cobalt oxide, manganese oxide, copper oxide vanadium oxide etc., have intensively been used due to their availability, chemically stability, mechanically, eco-friendly, and high performances in supercapacitor application [8, 9]. On this account, the introduction of transition metal oxide in CPs has gained more attention, which shows good expandability, chemical resistance and cation exchange ability [10, 11]. Among these, the introduction of V₂O₅ in CPs has attained a great deal of attention due to their various promising properties including their interesting charge transport characteristics, that make them suitable for various applications [12, 13]. The interaction between CP and V₂O₅ influences the polymer conformation, chain length, and electron transport properties [12]. Moreover, the synergistic effects of V₂O₅ and CPs generate the electron transport between the CP and V₂O₅, which ultimately led to the development of new properties.

Literature reveals that several groups have reported the composite of V₂O₅ with different CPs like polypyrrole, polyaniline, polythiophene and their derivatives. However, the Polyaniline (PANI) and its derivatives (alkyl or aryl substituted) have extensively been studied because of their good solubility and ease of synthesis [14]. Amongst these, Polydiphenylamine (PDPA), an N-substituted derivative of PANI, consisting intermediate properties of polyaniline and poly (phenylene) have emerged as a new conducting polymer [15]. Several reports have been published for the chemical and electrochemical synthesis of PDPA and PDPA composite [16, 17]. It has been noted that the synthesis and morphology of CPs and CP based composites are strongly affected by the selection of different catalysts and the reaction media used [18]. For instance, Tao et al. [19] have reported the synthesis of aniline oligomers in alkaline solution, which was further used as a seed to grow the PANI nanofibers in acidic solution. Further, they have reported that the synthesis is low cost environment friendly. Further, in a study reported by Katarzyna et al. [20], the effect of reaction medium (m-cresol, DMSO, and NMP) on conductivity and morphology of PANI doped with camphorsulphonic acid. They have inferred that the composite synthesized in presence of m-cresol, exhibited good conductivity and uniform and continuous polymer films. While the composite with DMSO and NMP, showed non-uniform and granular films with lower conductivity. To the best of our knowledge, no work has been reported till date on the influence of reaction medium (aqueous and acidic) in the processing of PDPA and PDPA/V₂O₅ composite. Interestingly V₂O₅, in these reaction mediums is able to alter the bulk properties of PDPA and PDPA/V₂O₅ composite.

On this account, here we report one pot facile synthesis of polydiphenylamine/V₂O₅ composite in two different media i.e. aqueous (H₂O) and acidic (HCl). The influence of these media on their structural, morphological, thermal and electrical behaviour was investigated. It was found that in aqueous medium PDPA/V₂O₅ composite has formed, which exhibited better thermal and electrical properties than PDPA polymer that synthesized in acidic medium.

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