Influence of medium on structure, morphology and electrochemical properties of polydiphenylamine/vanadium pentoxide composite
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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/V2O5 composite shows good electrochemical properties.
KeywordsPolydiphenylamine Vanadium pentoxide Reaction medium Electrochemical properties
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 . 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 . 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 . 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 . 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 . For instance, Tao et al.  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. , 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.
Diphenylamine (DPA) monomer (C12H11N, mol. wt. 169.22) Merck Germany, Vanadium pentoxide (V2O5, mol. wt. 181.88) Thomas baker chemicals, Ammonium peroxydisulphate (APS, mol. wt. 228) Alfa Aesar, hydrochloric acid (HCl, mol. wt. 36.46, %assay 36.5, sp. gravity 1.18) Merck India and distilled water.
PDPA/V2O5 was synthesized according to our previously reported work . However, to investigate the effect of medium, the same was synthesized in acidic medium. In the process, 0.507 g (0.01 mol) fine powder of vanadium pentoxide (V2O5) was dissolved in 50 mL of 1 M HCl and taken in a round bottom flask fitted with thermometer, ice bath and magnetic stirrer. Further, the addition of 1.69 g (0.01 mol) of DPA monomer was carried out that provides pre-oxidative polymerization of DPA, which was established by the change in colour from yellow to light green. After this, 50 mL of 0.01 m APS aqueous solution was added dropwise that further changes the colour from light to dark green indicating that APS promotes the oxidising ability of V2O5 in HCl medium. The reaction was further proceed for 24 h. After the completion of reaction, precipitate of was filtered, washed and dried at 80 °C for 24 h in oven.
This indicates that the presence of V2O5 alone does not contribute to the polymerization of DPA, as no change in colour was observed. This behaviour suggest that the V2O5 does not participate in the oxidation of DPA monomer for its polymerization. However, V2O5 gets enveloped by PDPA and formed PDPA/V2O5 composite. The reaction was further allowed to proceed for 24 h. After the completion of reaction, the precipitate of PDPA/V2O5 composite was filtered, washed with distilled water and methanol repeatedly until the filtrate become colourless. The collected composite was dried at room temperature (37 °C) followed by further drying at 80 °C for 24 h in oven.
2.3 Materials characterization
The structural characterization of the PDPA polymer and PDPA/V2O5 composite was carried out with the help of Fourier Transform Infrared (FTIR) spectra (Shimadzu FT-IR spectrometer) using KBr pellets. The advance X-ray diffractometer (Rigaku Rodaflex 200B) was used to record the X-ray diffraction (XRD) patterns at the 2θ range of 10°–70° using Cu Kα radiation. The morphology and elemental analysis were characterized by SEM and EDS analysis using EVO18, Carl Zeiss, Germany equipped with EDS detector. The electrical properties of PDPA/V2O5 composite and PDPA were characterized by temperature dependent DC conductivity meter in the temperature range 364–463 K. For measuring the DC conductivity, the pellets of the synthesized composites were used. A constant voltage of 1.5 V was applied across the pellets and measured the current. The temperature was measured with the help of copper-constantan thermo couple, which was kept between the two steel electrodes.
The electrochemical property of polymer and polymer composite was studied by cyclic voltammetry, measured by Autolab type III potentiostat (μ3AVT70762 Netherland). The measurement was carried out in 0.5 M H2SO4 aqueous solution on a standard three-electrode system using platinum wire as a counter electrode and Ag/AgCl (saturated KCl) as the reference electrode, respectively. The CV curves were recorded in the potential window from + 1.2 to − 1.2 V (vs. Ag/AgCl) at scan rate of 2 mV/s. Electrochemical cyclic stability of the electrodes were also carried out by CV over 200 cycles. The electrochemical impedance measurements were carried out in a frequency range of 10 Hz–100 MHz using Wayne Kerr 6500B instrument.
3 Results and discussion
3.4 Thermal stability
3.5 Electrical conductivity
The temperature dependent DC conductivity was measured in the temperature range of 364–463 K using constant voltage of 1.5 V, which is shown in Fig. 6. The dc conductivity of both PDPA and PDPA/V2O5 composite increased with the increasing temperature, this can be attributed to the increase in thermal vibration activity that led to the formation of polaron and bipolaron along the conjugated chains of the polymers. Thus, the mobility of charge carriers (polarons and bipolarons) increases with the increase in temperature that led to the increase in the electrical conductivity .
3.6 Dielectric properties
3.7 Electrochemical properties
The electrochemical properties (capacitance and resistance) of PDPA and PDPA/V2O5 composites were further examined with the help of EIS measurement. The imaginary impedance (Z’’) versus real impedance (Z’) is a Nyquist plot (Fig. 9b) of the same was recorded. The curves exhibit a semicircle at high and low frequency region, which corresponds to the charge transfer reaction at electrode/electrolyte interface [37, 38]. The PDPA/V2O5 composite displayed a semicircle with smaller diameter than that of PDPA. This indicates that the PDPA/V2O5 composite exhibits low impedance on electrode–electrolyte interface .
Resistance and capacitance values (fitted to the parameters in the Nyquist plot) of PDPA/V2O5 and PDPA
Resistance and capacitance
Various properties of PDPA/V2O5 composite and PDPA polymer
Conductivity S cm−1
Char residue (%)
Dielectric constant (ɛ)
7.44 × 10−5
3.0 × 10−6
In the present study, we have discussed the influence of reaction medium (aqueous and acidic) on the formation of PDPA and PDPA/V2O5 composite for the first time. The synthesis were facile and one pot. The structural, morphological, electrical and thermal properties are tuned just by the changing the reaction medium i.e. acidic to aqueous medium. XRD and EDX analysis revealed that in aqueous medium PDPA/V2O5 composite has formed, while in case of acidic medium only the PDPA polymer is formed, as in acidic medium V2O5 acts only as a catalyst that finally leaches out. Additionally, SEM analysis revealed that the PDPA showed granules while PDPA/V2O5 exhibits rod like morphology. TGA studies revealed that PDPA/V2O5 composite displayed excellent thermal properties (i.e. char residue of 43% at 850 °C) than PDPA (char residue of 29% at 850 °C). The electrical conductivity at 463 K for PDPA/V2O5 composite was found to be 7.44 × 10−5 S cm−1, which is higher than that of PDPA (2.36 × 10−6 S cm−1). Moreover, PDPA/V2O5 composite exhibited superior dielectric properties (i.e. dielectric constant of 257.32 at 1 kHz), which is much higher than that of PDPA (218.39 at 1 kHz). Thus, these studies revealed that the aqueous medium is suitable for the synthesis of PDPA/V2O5 composite to avail better properties. Thus, it can be concluded that PDPA/V2O5 composite has a potential scope in the field of energy storage devices e.g. capacitor and batteries.
One of the author, Halima Khatoon, gratefully acknowledge MANF-UGC (F1-17.1/2014-15) for financial assistance. We further extend our sincere thanks to Dr. Javed Alam, Department of Physics, Jamia Millia Islamia, for temperature dependent dc conductivity measurement.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interests.
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