Role of Dielectric Constant on Ion Transport: Reformulated Arrhenius Equation

Solid and nanocomposite polymer electrolytes based on chitosan have been prepared by solution cast technique. The XRD results reveal the occurrence of complexation between chitosan (CS) and the LiTf salt. The deconvolution of the diffractogram of nanocomposite solid polymer electrolytes demonstrates the increase of amorphous domain with increasing alumina content up to 4 wt.%. Further incorporation of alumina nanoparticles (6 to 10 wt.% Al2O3) results in crystallinity increase (large crystallite size). The morphological (SEM and EDX) analysis well supported the XRD results. Similar trends of DC conductivity and dielectric constant with Al2O3 concentration were explained. The TEM images were used to explain the phenomena of space charge and blocking effects. The reformulated Arrhenius equation (σ(ε′,T)=σoexp(-Ea/KBε′T)) was proposed from the smooth exponential behavior of DC conductivity versus dielectric constant at different temperatures. The more linear behavior of DC conductivity versus 1000/(ɛ′×T) reveals the crucial role of dielectric constant in Arrhenius equation. The drawbacks of Arrhenius equation can be understood from the less linear behavior of DC conductivity versus 1000/T. The relaxation processes have been interpreted in terms of Argand plots

Structure, Dielectric Properties and AC Behavior of Commercial Polytetrafluroethylene (PTFE) Polymer

In this work the relative permittivity (ε''), dielectric loss (ε'') and AC-conductivity for commercial polytetrafluroethylene (PTFE) have been measured at different temperatures (20-110°С) and over the frequency range from 10 KHz to 1 MHz. The infrared (IR) spectra of PTFE also been investigated to detect the presence of polar groups and carbon double bonds. The relative permittivity had observed to decrease with increasing frequency and temperature. Some loss peaks were observed in the dielectric loss spectra, which referred to the relaxation, arises from the orientation of unsaturated double (C=C) bond and polar additives. The diameter of the semicircles in Cole-Cole (ε' versus ε'') plots are not coincides with x-axis at different temperature which reveals that the relaxation processes are non-Debye type. The AC-conductivity increases with increasing of frequency and almost independent on the temperature

New Method for the Development of Plasmonic Metal-Semiconductor Interface Layer: Polymer Composites with Reduced Energy Band Gap

Silver nanoparticles within a host polymer of chitosan were synthesized by using in situ method. Ultraviolet-visible spectroscopy was then carried out for the prepared chitosan : silver triflate (CS : AgTf) samples, showing a surface plasmonic resonance (SPR) peak at 420 nm. To prepare polymer composites with reduced energy band gap, different amounts of alumina nanoparticles were incorporated into the CS : AgTf solution. In the present work, the results showed that the reduced silver nanoparticles and their adsorption on wide band gap alumina (Al2O3) particles are an excellent approach for the preparation of polymer composites with small optical band gaps. The optical dielectric loss parameter has been used to determine the band gap experimentally. The physics behind the optical dielectric loss were interpreted from the viewpoint of quantum mechanics. From the quantum-mechanics viewpoint, optical dielectric loss was also found to be a complex equation and required lengthy numerical computation. From the TEM investigation, the adsorption of silver nanoparticles on alumina has been observed. The optical micrograph images showed white spots (silver specks) with different sizes on the surface of the films. The second semicircle in impedance Cole-Cole plots was found and attributed to the silver particles

The effect of number of vacuum thermal evaporation cycles to the optoelectronic and morphological properties of ZnO

Zinc oxide (ZnO) is a wide band gap material (~3.37 eV) which has small exciton Bohr radius ~2.34 nm. In dye-sensitized solar cell, ZnO thin film is used as photoelectrode. Light-sensitive organic/ inorganic fluorophores could be adsorbed on the surface of the ZnO film, which later will be sandwiched with electrolyte and a counter electrode. The aim of this paper is to study the effect of number of evaporation cycle to the yielded morphology and size of ZnO building blocks; deposited using one, two, and three cycles of vacuum thermal evaporation technique. The ZnO thin films have been deposited on ITO glass substrate at vacuum pressure of 5 ´ 10-5 Torr, 116 A, and 2.6 V. The morphology of the thin films has been examined under Field Emission Scanning Electron Microscope (FESEM), which showed nanosphere morphology. The morphological observation is supported by a simulation; which calculated based on the crystallographic properties of the synthesized ZnO – characterized by X-ray diffractometer (XRD). Three sets of the ZnO thin films consists of ZnO particles in the range of 8 – 20 nm, 11 – 37 nm, and 6 – 16 nm respectively. According to the optical properties characterized by absorption spectrometer, it has been observed that the band gap of the thin films increased with increasing number of evaporation cycles. The values of the optical bandgap, Eg evaluated from Tauc’s plot, were found in the range between 2.40 eV to 2.60 eV

Characterization of opto-electronic properties of thermally evaporated ZnO

Photoelectrode plays significant role in excitonic solar cells i.e., (i) as an acceptor and (ii) transport media of excited state electron from the fluorophore upon absorption of energy of photon; which prevents from electron-hole recombination in the fluorophore. The evolution of opto-electronic properties of the ZnO upon change of size, however, receives insufficient attention from researchers. Therefore, the aim of this paper is to establish few realistic clusters of (ZnO)n (n = 3, 6, 12, 13, and 21) to study their opto-electronic properties using quantum chemical calculations at the level of B3LYP functional and lanl2dz basis set. Geometry of the clusters were optimized to the lowest energy structures; evaluated as realistic using a combination of harmonic frequency calculations, and experimental works. A device structure of cadmium selenide-based solar cell was used in the study to analyze the energy level alignment, and compatibility of the ZnO realistic clusters

Effect of ohmic-drop on electrochemical performance of EDLC fabricated from PVA:dextran:NH4I based polymer blend electrolytes

Proton conducting solid polymer blend electrolytes based on poly(vinyl alcohol)(PVA):dextran that were doped with different quantities of ammonium iodide (NH4I) were prepared. The X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) study were carried out to examine the compatibility of NH4I withPVA:dextran polymers. FTIR spectroscopy assessment was used to establish the presence of a complex formation between the PVA:dextran and added salt through the modification and reduction in the intensity of FTIR bands relevant to the functional groups. The field emission scanning electron microscopy (FESEM) examination was used to assess the channels for proton transport. Electrical impedance spectroscopy (EIS) was used to analyse the samples conductivity behaviour. The sample with 20 wt.% of added salt has shown a high DC conductivity which can be employed in electrochemical devices such as EDLC. It is also demonstrated by the transference number (TNM) and linear sweep voltammetry (LSV) that it is appropriate to use the largest conducting sample for electrochemical device. There was electrochemical stability of the electrolyte sample with voltage sweeping linearly to 1.3 V. It is shown by the outcome of cyclic voltammetry (CV) plot that charge storage at the site of electrode-electrolyte is non-Faradiac. A high drop voltage (Vd=IR) is implied by the usual galvanostatic charge-discharge. The equivalent series resistance (Res) increases as a result of the increase in Vd all the way through the charge-discharge cycle. Specific capacitance (Csp) is nearly constant from the foremost cycle to the 100th cycle, with average of 4.2 F/g

Compatible solid polymer electrolyte based on methyl cellulose for energy storage application: structural, electrical, and electrochemical properties

Compatible green polymer electrolytes based on methyl cellulose (MC) were prepared for energy storage electrochemical double-layer capacitor (EDLC) application. X-ray diffraction (XRD) was conducted for structural investigation. The reduction in the intensity of crystalline peaks of MC upon the addition of sodium iodide (NaI) salt discloses the growth of the amorphous area in solid polymer electrolytes (SPEs). Impedance plots show that the uppermost conducting electrolyte had a smaller bulk resistance. The highest attained direct current DC conductivity was 3.01 × 10−3 S/cm for the sample integrated with 50 wt.% of NaI. The dielectric analysis suggests that samples in this study showed non-Debye behavior. The electron transference number was found to be lower than the ion transference number, thus it can be concluded that ions are the primary charge carriers in the MC–NaI system. The addition of a relatively high concentration of salt into the MC matrix changed the ion transfer number from 0.75 to 0.93. From linear sweep voltammetry (LSV), the green polymer electrolyte in this work was actually stable up to 1.7 V. The consequence of the cyclic voltammetry (CV) plot suggests that the nature of charge storage at the electrode–electrolyte interfaces is a non-Faradaic process and specific capacitance is subjective by scan rates. The relatively high capacitance of 94.7 F/g at a sweep rate of 10 mV/s was achieved for EDLC assembly containing a MC–NaI system

The Study of Plasticized Amorphous Biopolymer Blend Electrolytes Based on Polyvinyl Alcohol (PVA): Chitosan with High Ion Conductivity for Energy Storage Electrical Double-Layer Capacitors (EDLC) Device Application

In this study, plasticized films of polyvinyl alcohol (PVA): chitosan (CS) based electrolyte impregnated with ammonium thiocyanate (NH4SCN) were successfully prepared using a solution-casting technique. The structural features of the electrolyte films were investigated through the X-ray diffraction (XRD) pattern. The enrichment of the amorphous phase with increasing glycerol concentration was confirmed by observing broad humps. The electrical impedance spectroscopy (EIS) portrays the improvement of ionic conductivity from 10−5 S/cm to 10−3 S/cm upon the addition of plasticizer. The electrolytes incorporated with 28 wt.% and 42 wt.% of glycerol were observed to be mainly ionic conductor as the ionic transference number measurement (TNM) was found to be 0.97 and 0.989, respectively. The linear sweep voltammetry (LSV) investigation indicates that the maximum conducting sample is stable up to 2 V. An electrolyte with the highest conductivity was used to make an energy storage electrical double-layer capacitor (EDLC) device. The cyclic voltammetry (CV) plot depicts no distinguishable peaks in the polarization curve, which means no redox reaction has occurred at the electrode/electrolyte interface. The fabricated EDLC displays the initial specific capacitance, equivalent series resistance, energy density, and power density of 35.5 F/g, 65 Ω, 4.9 Wh/kg, and 399 W/kg, respectively

Morphological and Optical Characteristics of Chitosan(1−x):Cuox (4 ≤ x ≤ 12) Based Polymer Nano-Composites: Optical Dielectric Loss as an Alternative Method for Tauc’s Model

In this work, copper (Cu) nanoparticles with observable surface plasmonic resonance (SPR) peaks were synthesized by an in-situ method. Chitosan host polymer was used as a reduction medium and a capping agent for the Cu nanoparticles. The surface morphology of the samples was investigated through the use of scanning electron micrograph (SEM) technique. Copper nanoparticles appeared as chains and white specks in the SEM images. The strong peaks due to the Cu element observed in the spectrum of energy dispersive analysis of X-rays. For the nanocomposite samples, obvious peaks due to the SPR phenomena were obtained in the Ultraviolet-visible (UV-vis) spectra. The effect of Cu nanoparticles on the host band gap was understood from absorption edges shifting of absorption edges to lower photon energy. The optical dielectric loss parameter obtained from the measurable quantities was used as an alternative method to study the band structure of the samples. Quantum mechanical models drawbacks, in the study of band gap, were explained based on the optical dielectric loss. A clear dispersion region was able to be observed in refractive indices spectra of the composite samples. A linear relationship with a regression value of 0.99 was achieved between the refractive index and volume fractions of CuI content. Cu nanoparticles with various sizes and homogenous dispersions were also determined from transmission electron microscope (TEM) images

Structural, Impedance and Electrochemical Characteristics of Electrical Double Layer Capacitor Devices Based on Chitosan: Dextran Biopolymer Blend Electrolytes

This report presents the preparation and characterizations of solid biopolymer blend electrolyte films of chitosan as cationic polysaccharide and anionic dextran (CS: Dextran) doped with ammonium iodide (NH4I) to be utilized as electrolyte and electrode separator in electrical double-layer capacitor (EDLC) devices. FTIR and XRD techniques were used to study the structural behavior of the films. From the FTIR band analysis, shifting and broadening of the bands were observed with increasing salt concentration. The XRD analysis indicates amorphousness of the blended electrolyte samples whereby the peaks underwent broadening. The analysis of the impedance spectra emphasized that incorporation of 40 wt.% of NH4I salt into polymer electrolyte exhibited a relatively high conductivity (5.16 × 10−3 S/cm). The transference number measurement (TNM) confirmed that ion (tion = 0.928) is the main charge carriers in the conduction process. The linear sweep voltammetry (LSV) revealed the extent of durability of the relatively high conducting film which was 1.8 V. The mechanism of charge storage within the fabricated EDLC has been explained to be fully capacitive behavior with no redox peaks appearance in the cyclic voltammogram (CV). From this findings, four important parameters of the EDLC; specific capacitance, equivalent series resistance, energy density and power density were calculated as 67.5 F/g, 160 ohm, 7.59 Wh/kg and 520.8 W/kg, respectively