3.1 FTIR Analysis
The functional groups present in samples PTh and the binary polymer nanocomposite (PTh-nAg2O) were studied using the FTIR spectroscopy technique. The spectra were recorded between 4000 cm− 1 and 400 cm− 1 in wavelength. Figure 1a shows the FTIR spectrum of the polymer, which has characteristic absorption peaks at 3448, 1635, 1404, 1335, 1173, 1119, 1034, 679, and 486 cm− 1 corresponding to the O-H stretching vibration, C = C asymmetric stretching vibration, C = C symmetric stretching vibration, C-N stretching vibration, C-H in-plane deformation, C-H bending vibration, C-H inplane bending vibration, C-S stretching vibration, and C-S-C ring deformation, respectively [22, 23]. Figure 1b shows all the characteristic peaks of polymers with some slight spectral intensity changes in the binary polymer nanocomposite (PTh-nAg2O) FTIR spectrum, in which the peaks of PTh at wave numbers 1404, 1335, 1173, 679, and 486 cm− 1 were shifted to 1427,1366, 1196, 694, 478 cm− 1, respectively [24–26].
Figure 1 FTIR Spectrum of a) PTh, b) Binary polymer nanocomposite (PTh-nAg2O).
In Fig. 1b, the peak seen at 3448 cm-1 may be due to O-H stretching and deformation assigned to the water adsorption on the metal surface. The absorption band observed at 1628 cm-1 Ag − O are due to stretching vibration [25], while the band at 694 cm-1 corresponds to Ag-O interaction [27, 28].
3.2 XRD Analysis
The size phase and crystallinity of the synthesized samples were determined by analyzing their XRD patterns. The powder was analyzed between 20° to 80° using a Cukα source (λ = 1.54178A ͦ) at a rotation speed of 6° with a voltage of kV and a current of 30mA. The resultant XRD pattern is shown in Fig. 2a and 2b. The existence of strong and sharp diffraction peaks located at 2θ = 27.8°, 32.39°, 38.19°, 46.42°, 54.90°, 57.56°, 67.48°, 74.73°, 76.67° and the corresponding lattice planes are related to (1 1 0), (1 1 1), (2 0 0), (2 1 1), (2 2 0), (2 2 1), (3 1 1), (2 2 2), (1 2 3), respectively. The obtained results are well in accordance with a standard ICDD file No: 761393, Which is indexed to the face-centred cubic structure, indicating they have a relatively high degree of crystallinity. In the XRD pattern of the PTh-nAg2O polymer nanocomposite, the planes (111) and (110) represent the pointers of silver oxide nanoparticles, and the peaks (211) and (220) correspond to the face-centred cubic crystal structure [27, 28].
Figure 2 XRD pattern of a) PTh, b) Binary polymer nanocomposite (PTh-nAg2O).
The Debye's Scherrer relation is given by Eq. (1), and it is used to calculate the average crystalline size of the binary polymer nanocomposite (PTh-nAg2O),
--------(1)
Where D is the crystalline size, λ is the X-Ray wavelength 1.5418 Aº, θ is the half diffraction angle of the peak (in degrees), and β is the true half peak width. This increase in the XRD peak's intensity could indicate that metal oxide nanoparticles are well disseminated in the polymer matrix. The Binary polymer nanocomposite (PTh-nAg2O), 2ϴ values and corresponding hkl planes, d-spacing, and relative intensity values are shown in Table.1.
Table. 2 XRD values of Binary polymer nanocomposite (PTh-nAg 2 O).
The sharpness and clarity of the peak indicate the crystallinity of the synthesized materials. The crystalline size of binary polymer nanocomposite (PTh-nAg2O) has been estimated and it is around 29 nm.
3.3 UV-VIS Spectroscopy
The UV-visible spectrum of PTh and Binary polymer nanocomposite (PTh-nAg2O) are shown in Figs. 3a & 3b. It demonstrates that the absorption spectra of PTh exhibit an absorption peak at 300 nm caused by the PTh rings Π- Π* inter-band transition [5]. Both synthesized samples' band gap energies were determined using the equation
Band gap (E g ) = hc/λ ------- (2).
Where Eg is the band gap, h is Planck's constant, c is the velocity of light (m/s), λ is the wavelength (nm). Band gap Energy (E) for PTh and Binary polymer nanocomposite (PTh-nAg2O) are 4.27eV and 2.663 eV, respectively. The absorption maximum for PTh is 290 nm. Whereas for Binary polymer nanocomposite (PTh-nAg2O) the value is 455nm [32, 33].
Figure 3 UV-Vis Spectrum of a) PTh, b) Binary polymer nanocomposite (PTh-nAg2O).
The λmax value shift from 290 nm to 455 nm is caused by the interaction of nanosilver oxide with polythiophene. It is well understood that the interaction of Ag2O nanoparticles with polymers causes a change in the polymer's stability and, consequently, in the polymer’s structure. Due to the flaws, there are more localized states in the band gap, which lowers the band gap energy of the polymer. [34].
3.4 Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) was used to examine the surface morphology of polymers and polymer nanocomposites. The surface morphology of the polymer PTh and its binary polymer nanocomposite (PTh-nAg2O) are shown in Figs. 4a and 4b, respectively. Figure 4a shows an SEM micrograph of the polymer PTh, which has an unclear spherical-shaped polymer structure, is agglomerated, and forms clusters-like stringent in the PTh [6]. Figure 4b represents SEM micrograph of the Binary polymer nanocomposite (PTh-nAg2O), which shows the agglomeration of Ag2O particles with a polymer matrix and stringent surface broken into the uneven crystalline surface. Based on the structural differences between the polymer and its binary polymer nanocomposite, we can conclude that good contact between PTh and binary polymer nanocomposite (PTh-nAg2O) improves electron transport, thereby increasing specific capacitance [27].
Figure 4 SEM images of a) PTh, b) Binary polymer nanocomposite (PTh-nAg2O).
3.5 Field Emission Scanning Electron Microscopy (FESEM)
The FE-SEM image of PTh and its binary polymer nanocomposite (PTh-nAg2O) are shown in Figs. 5a and 5b. PTh polymer matrix displays a hard-stringent surface area [35], as shown in Fig. 5a. In Fig. 5b, binary polymer nanocomposite (PTh-nAg2O) shows the dispersion of Ag2O nanoparticles with PTh. As a result, the rough surface of the polymer was changed into a smooth surface, relatively uniform in polymer nanocomposites. The FESEM image of polythiophene has a hard-stringent surface area. Due to the polymer's surface absorption property, some of the silver oxide nanoparticles in the binary polymer nanocomposite appeared to be incorporated into the polymer matrix, and they began to aggregate (a tendency to combine and form agglomerates) (PTh-nAg2O). The absorption and intercalation of Ag2O on the polymer matrix could explain the morphological change [36].
Figure 5 FESEM images of a) PTh, b) Binary polymer nanocomposite (PTh-nAg2O) polymer nanocomposite
3.6 EDX Spectrum
The EDX spectrum of the binary polymer nanocomposite (PTh-nAg2O) is shown in Fig. 6. The presence of Ag metal around 40.92 and oxygen around 14.27 are confirmed in the EDX spectrum, as shown in the Figure. 6.
Figure 6 SEM-EDX images of Binary polymer nanocomposite (PTh-nAg2O).
3.7 A.C CONDUCTIVITY MEASUREMENTS
Utilizing the two-probe method, the PSM 1735 frequency response analyzer was used to evaluate the A.C. conductivity of the polymer and its binary polymer nanocomposite within the frequency range from 1Hz to 10MHz. using Eq. (3),
σA.C = εoεrωtanσᵟ s/cm ------- (3)
In the equation, where εo is the permittivity of the free space, εr is the material’s dielectric constant.
ω = 2πf ------- (4)
Where f is the frequency, tanᵟ is the dielectric loss.
The electrical conductivity of binary polymer nanocomposite (PTh-nAg2O) and PTh was calculated to be 1.76 x 10− 7 S/cm and 2.00 x 10− 5 S/cm, respectively. The magnitude of conductivity of the binary polymer nanocomposite (PTh-nAg2O) is two orders greater than that of pure polythiophene, as measured by A.C. conductivity values. These electrical conductivity results show that the binary polymer nanocomposite (PTh-nAg2O) has a higher electrical conductivity than the polymer PTh. The increase in polymer nanocomposite conductivity may also be attributable to electron delocalization; the dopant Ag2O nanoparticle also plays an important role in the conductivity level [35]. Because of the dispersion of Ag2O nanoparticles in the polymer matrix, mobile charge carriers are injected into the polymer backbone, resulting in increased conductivity in binary polymer nanocomposite (PTh-nAg2O) [37]. The increase in conductivity due to charge carrier propagation increased as the filler quantity in the polymer nanocomposite increased [38].
Figure 7 Conductivity measurements of a) PTh b) Binary polymer nanocomposite (PTh-nAg2O) polymernanocomposite.
The findings reveal that nanocomposite materials have higher electrical conductivity than PTh. The nano metal particles inserted into the polymer matrix are responsible for the increased conductivity of the binary polymer nanocomposite (PTh-nAg2O). Doping may have increased the A.C conductivity of the binary polymer nanocomposite (PTh-nAg2O) due to the equal distribution of nanoparticles and an increase in crystallite density per unit space, as revealed by XRD. The mixture of crystalline and amorphous features in the composite material may also contribute to improved conductivity. [39, 40].
3.8 Cyclic Voltammetry
Using cyclic voltammetry in a 1 M H2SO4 solution at room temperature, the performance of these synthesized samples as supercapacitor electrodes were analyzed. Electrochemical experiments were carried out in a three-electrode cell with a voltage window ranging from 0 to 1V. The cyclic voltammetry of the PTh and PTh-nAg2O polymer nanocomposite is shown in Figs. 8a and 8b. The cyclic curves are measured from three electrodes system and carried out under different scan rates from 10 to 50 mVs− 1. All curves show an increase in cyclic behaviour as the scan rates are increased from 10 to 50 mVs− 1, which is common in supercapacitor research. In contrast to the two synthetic materials, Binary polymer nanocomposite (PTh-nAg2O) outperforms significantly. According to cyclic voltammetry, CV loops gradually increased from 10 mVs− 1 to 50 mVs− 1 cycles in the cyclic voltammetry measurements.
The specific capacitance of materials is calculated from Eq. (5).
C sp = (I*Δt/)/(m*ΔV) F/g--------- (5)
in which the product of current (I) and the discharging time (t) are divided by the product of the potential drop during discharge (V) and the material mass (m).
Figure 8: Cyclic voltammetry measurements of a) PTh b) Binary polymer nanocomposite (PTh-nAg2O)
For PTh and binary polymer nanocomposite (PTh-nAg2O), the curves distorted the rectangular geometry, irrespective of the low scan rate of 10–50 mVs− 1, which might be attributed to the higher equivalent serial resistance (ESR) of the composite electrode that becomes a dominant factor at a high scan rate of more than 10 mVs− 1 [41]. The wider area coverage of the curve reveals exceptional charge storage performance. [42]. The scan rate versus the specific capacitance diagram is given in Fig. 9.
Figure 9 Specific Capacitance Versus Scan rate Diagram of Binary polymer nanocomposite (PTh-nAg2O).
According to the CV diagram, specific capacitance increases with decreasing scan rate or decreases with increasing scan rate due to decreased electrolyte ion diffusion to the electrode material's active site, resulting in a decrease in diffusion time [43, 44]. Table. 2 shows a comparison of previous and current research findings on specific capacitance values of silver oxide-based polymer nanocomposites. At the lowest scan rate, the specific capacitance values of the binary polymer nanocomposites (PTh-nAg2O) produced are 725 F/g, respectively.
3.8.2 Electron Impedance Spectroscopy
Figure 10 depicts the electrochemical impedance spectroscopy result of the binary polymer nanocomposite (PTh-nAg2O) using a Nyquist plot. EIS measurements were performed to understand the electrochemical reaction and conductivity of the materials under investigation. The Nyquist impedance graph displays the imaginary and real components of the impedance throughout the frequency range from 1 Hz to 100 kHz. In the Nyquist plot, the semicircle diameter (Rct) shows charge transfer resistance on the electrode surface (Rs), which was calculated by the intercept of the plot at the real axis. This Rs value indicates the total resistance of the electrochemical system. In EIS measurements, Figs. 9a and 9b show the semicircle is invisible.
Figure 10 Nyquist plot of a) PTh b) Binary polymer nanocomposite (PTh-nAg2O) polymer nanocomposite
The plot shows two regions in all the electrode materials: high- and low-frequency regions. The high-frequency region is associated with interfacial processes. At low frequencies, with an ideal capacitor, the imaginary portion of the impedance spectrum associated with the capacitive behaviour of the charging mechanism usually forms a 90° vertical line. Charge carrier buildup is connected to the diameter of the semicircle zone, which influences frequency-dependent ionic conduction or transport in the electrolyte and spikes. [44]. As the inclined angle is less than a straight angle, it is possible to see nonhomogeneity in the electrolyte/electrode interface. Since the spur should be vertical for an ideal capacitance, the Rct value of the binary polymer nanocomposite (PTh-nAg2O) nanocomposite corresponds to the lowest frequency region relative to PTh. [45, 46]. In comparison to PTh and other nanocomposites, the Rct value of the binary polymer nanocomposite (PTh-nAg2O) is in the region of the lowest frequency. Electrochemical experiments on binary polymer nanocomposite (PTh-nAg2O) have demonstrated enhanced electrochemical performance.