Contribution Of Electrode Polarization Research Articles

Ionic transport and segmental dynamics in poly(ethylene oxide) based polymer electrolytes: Dependence on molecular weight of host polymer matrix

We have investigated the ion transport and segmental dynamics in poly(ethylene oxide) (PEO) and sodium tetrafluoroborate (NaBF4) salt based solid polymer electrolytes as a function of molecular weight of PEO polymer matrix at a fixed salt concentration (EO/Na = 18) using broadband dielectric spectroscopy. The molecular weight (Mv) of PEO polymer matrix was varied from 1 × 105 to 6 × 105 g/mol. The ionic conductivity of the PEO based electrolytes obtained from the complex impedance plot showed a correlation with the glass transition temperature, crystallinity and ion diffusion coefficient. The AC conductivity spectra were analyzed by using the universal power law model, except the low frequency region, where the electrode polarization contribution was dominant. The temperature dependence of ionic conductivity and the hopping frequency followed the Vogel-Tammann-Fulcher (VTF) relation, indicating a coupling between the ion transport and the segmental dynamics of polymer chains. The segmental dynamics was investigated using the derivative dielectric constant spectra. The modulus spectra were well described by the Havriliak-Nigami and the Kohlrausch-Williams-Watts functions. The temperature dependence of the conductivity relaxation time also followed the VTF relation. The ion transport in PEO based polymer electrolytes with higher molecular weight was found more cooperative than that of the other polymer electrolytes.

Non-overlapping small polaron and overlapping large polaron assisted conduction relaxation in polycrystalline YFe0·9Cr0·1O3 – An impedance spectroscopic and AC conductivity studies

Detailed ac electrical investigations within the frequency range 100 Hz-1 MHz have been conducted on the polycrystalline YFe 0·9 Cr 0·1 O 3 samples prepared via solid state reaction route, in a broad thermal interval of 298–673 K. A systematic development of grain, grain boundary and electrode polarization contribution have been observed with increasing temperature. The thermal variation of the grain resistance (R g ) and grain boundary resistances (R gb ) followed the non-adiabatic small polaron hopping (SPH) model and is responsible for the long-range conduction with different values of the activation energies at different thermal regimes. The ac conductivity of the material exhibited series of dispersive regions with broad region, where the slope changes occurred up to 473 K. Above 473 K, appreciable dc conductivity in the material can be seen. Different dispersive regions in the conductivity spectrum obeyed single power law and power law variation (Aω n ).

Dielectric polarization and relaxation processes of the lithium-ion conducting PEO/PVDF blend matrix-based electrolytes: effect of TiO2 nanofiller

The effect of TiO2 nanofiller concentration on the dielectric polarization and relaxation processes of (75PEO/25PVDF)/25 wt% LiClO4–x wt% TiO2 (x = 0, 2, 5, 10, 15, and 20) compositions based nanocomposite solid polymer electrolyte (NSPE) films has been investigated by employing the dielectric relaxation spectroscopy. The SEM micrographs demonstrate that the dispersion of TiO2 nanoparticles enormously alters the spherulitic morphology with the development of some cracks, pores, and wrinkles of these solution-cast prepared NSPE films. The X-ray diffraction study confirms that the heterostructures of these NSPE materials are semicrystalline and their degree of crystallinity increases irregularly with the increase of TiO2 concentration, however the crystallinity of host polymer blend matrix of these electrolytes decreases. The complex dielectric permittivity spectra of these NSPE materials in the frequency range from 20 Hz to 1 MHz at 27 °C reveal that there is a dominant contribution of electrode polarization and interfacial polarization at lower frequencies, whereas the high frequency permittivity values attribute to dipolar and ionic polarizations. Four types of relaxation processes have been probed by the ‘master curve representation’ of the dielectric and electrical spectra of these solid ion–dipole complexes. It is observed that the addition of TiO2 nanoparticles up to 10 wt% in these electrolytes influences the dielectric properties anomalously, but a huge decrease in the dielectric polarization and increase in the relaxation times are noted resulting in a significant decrease in the ionic conductivity of the film at 20 wt% TiO2 concentration. The dependence of dc ionic conductivity of these lithium-ion conducting NSPE materials on the chain segmental relaxation time and also the degree of crystallinity has been explored. The results of these NSPE materials have also been compared with the TiO2 nanoparticles loaded different polymer matrices and salts based electrolytes and discussed appropriately. These lithium-ion based electrolyte films are accredited for the solid-state ion-conducting energy storing devices from their electrochemical parameters characterized by LSV, CV, and CA techniques.

Ion conduction and relaxation mechanism in ionogels embedded with imidazolium based ionic liquids

The impact of physicochemical properties of imidazolium based different ionic liquids such as BDMIMBF4, BMIMBF, and EMIMBF4 on the ion conduction and relaxation mechanisms in ionogels is investigated using broadband dielectric spectroscopy. The complex conductivity isotherms of these ionogels are analyzed using a universal power law coupled with a modified Poisson-Nernst-Planck model for the contribution of electrode polarization dominated in the low frequency region. The effect of electrode polarization is analyzed by using the Macdonald-Coelho model to determine free-ion diffusivity and number density in these ionogels. The relaxation process of ions is also systematically studied using electric modulus spectroscopy over wide frequency and temperature ranges. The temperature dependence of the ionic conductivity, free-ion diffusivity, and relaxation times follows the Vogel-Tammann-Fulcher relationship, indicating existence of coupling between the ion transport and segmental dynamics in these ionogels. The EMIMBF4 ionic liquid doped ionogel shows the highest ionic conductivity, lowest relaxation time, highest free-ion diffusivity and highest number density due to the smallest size of cations, highest static dielectric constant, and lowest viscosity of the EMIMBF4 ionic liquid. It is observed that the stretched exponents for different ionogels obtained from Havriliak-Negami and Kohlrausch-Williams-Watts fits of electric modulus are lower than unity, indicating highly nonexponential relaxation in the investigated ionogels.

Effectively improved ionic conductivity of montmorillonite clay nanoplatelets incorporated nanocomposite solid polymer electrolytes for lithium ion-conducting devices

Synergistic effects of lithium salt concentration and inorganic nanofiller incorporation on the ionic conductivity of polymer blend matrix based nanocomposite solid polymer electrolytes (NSPEs) have been examined. The montmorillonite (MMT) clay nanoplatelets incorporated NSPE films based on poly(ethylene oxide) and poly(methyl methacrylate) blend matrix with lithium tetrafluoroborate (LiBF4) ionic salt have been prepared by the solution-cast method followed by melt-press technique. The 1, 3, and 5 wt% MMT amounts along with 13.3 wt% LiBF4 amount as compared to the weight of polymer blend have been used for the preparation of NSPE films. X-ray diffractometer (XRD) and the Fourier transform infrared (FTIR) spectrometer have been employed for structural characterization of these NSPE films. The complex permittivity and ac electrical conductivity spectra are investigated by using the dielectric relaxation spectroscopy, whereas the electrochemical performance of these materials has been characterized by the electrochemical analyzer. The XRD patterns reveal that the NSPEs are predominantly amorphous and have the intercalated and exfoliated MMT platelets, whereas the relative changes in their FTIR spectra confirm the ion–dipolar–nanofiller interactions between the functional groups of the blended polymers, lithium ions, and the MMT nanoplatelets. The permittivity and conductivity spectra of these materials are analyzed for exploring the dominant contribution of electrode polarization and dipolar polarization in the low and high frequency regions, respectively, and the presence of relaxation processes associated with structural dynamics of the solid-state ion–dipolar complexes. It has been found that the NSPE of relatively fast polymer chain segmental dynamics exhibits higher ionic conductivity. The room temperature ionic conductivity of the 13.3 wt% LiBF4 containing SPE is found more than two times higher as compared to that of the SPE film having 9.7 wt% LiBF4. When the MMT is incorporated, the ionic conductivity of 13.3 wt% LiBF4 containing NSPEs enhances by about one order of magnitude at room temperature. The dc ionic conductivity of the 13.3 wt% LiBF4 containing SPE film is found 1 × 10–5 S/cm at 55 °C, whereas it is 1.65 × 10–5 S/cm at 27 °C for the 5 wt% MMT incorporated NSPE film. The significantly enhanced ionic conductivity with ions transference number close to unity, high electrochemical stability voltage window and good reversibility of these NSPE materials confirm their potential applications as ion conductor/separator for the development of all-solid-state ion conducting devices and the lithium-ion batteries.

Conductivity and dielectric permittivity studies of KI‐based nanocomposite (PEO/PMMA/KI/I2/ZnO nanorods) polymer solid electrolytes

In this present study, we have studied the relaxation behaviour and dynamics of charge carriers in poly(ethylene oxide; PEO)/poly(methyl methacrylate; PMMA) blend with potassium based iodide–triiodide redox couple as polymer solid electrolyte dispersed with different concentration of ZnO nanorods as fillers. Various composition of potassium iodide (KI)‐based nanocomposite (PEO/PMMA/KI/I2/x wt% ZnO nanorods, x = 0, 2, 4, 6, 8, and 10) polymer solid electrolytes (NCPSEs) films were prepared by solution casting technique. Structural properties of the prepared solid electrolytes are studied by X‐ray diffraction and Fourier transform infrared spectroscopy. Among the prepared NCPSEs, 6 wt% sample of solid electrolyte showed high conductivity of 4.698 × 10−5 S/cm. The relaxation and dynamics of charge carriers are studied by analyzing complex conductivity and dielectric permittivity through power law along with the contribution of electrode polarization and Havriliak–Negami formalism, respectively, for the prepared polymer solid electrolytes to find out their usefulness for dye‐sensitized solar cell applications. © 2018 Society of Plastics Engineers POLYM. COMPOS., 40:2919–2928, 2019. © 2018 Society of Plastics Engineers

Electrical property investigations and microstructure characterization of a nuclear borosilicate glass ceramic

Abstract The electrical properties of a borosilicate glass ceramic used as a conditioning matrix for nuclear waste management are investigated by impedance spectroscopy over frequency and temperature ranges from 1 Hz to 1 MHz and from room temperature to 500 °C respectively. The microstructure of the glass ceramic was studied by scanning electron microscopy which revealed a phase separation phenomenon. The single circle arcs obtained from a complex impedance plot ( − Z ' ' ( ω ) v s Z ' ( ω ) ) indicate a pure ionic conduction mechanism and no Maxwell-Wagner-Sillars (MWS) polarization effect. The dependence of ac conductivity on frequency follows Jonscher's power law (known as the UDR: Universal Dielectric Response) very well. The plateau at low frequency corresponding to dc conductivity ( σ d c or σ 0 ) is mainly associated with the long-distance motion of alkali ions and increases linearly with temperature in Arrhenius coordinates. Scaling of both conductivity and dielectric properties were performed to avoid electrode polarization contribution and to provide better understanding of the relaxation behaviour in this sample. The master curves obtained from Summerfield scaling and normalized peaks ( Z ' ' ( ω ) / Z m a x ' ' and M ' ' ( ω ) / M m a x ' ' ) formalism suggest a conductivity due to short and long range mobility for the lowest temperatures and only a long-range mechanism associated with a non-Debye relaxation process at higher temperatures.

Investigation of ionic conductivity and relaxation in plasticized PMMA-LiClO4 solid polymer electrolytes

Abstract We have studied ion conduction and relaxation in plasticized PMMA-LiClO4 solid polymer electrolyte for different salt concentrations over a wide range of temperature. We have measured the complex conductivity spectra in a wide frequency range of 0.01 Hz–3 GHz and analyzed the experimental results using the random barrier model coupled with the contribution of electrode polarization in low frequency region. The temperature dependence of ionic conductivity and charge carrier relaxation time obtained from the analysis follows Vogel-Tammann-Fulcher behavior. The nearly constant loss response has been observed at low temperatures and/or at high frequency region. The temperature and frequency range of nearly constant loss response depends on the salt concentration in polymer matrix. The electric modulus spectra have been used to study charge carrier relaxation further. The stretched exponent, obtained from Kohlrausch-Williams-Watts (KWW) function, indicates highly non-exponential relaxation in the polymer electrolytes.

Ion dynamics in AgI doped silver selenium-tellurite mixed former glasses

The ionic conductivity and the conductivity spectra of the glass compositions xAgI-(1-x)[yAg2O-(1-y)(0.5SeO2-0.5TeO2)] have been studied at different temperatures The activation energy for the dc conduction has been analyzed using the Anderson-Stuart model, and a correlation between the dc conductivity and the doorway radius has been obtained. We have analyzed the conductivity spectra using the random free-energy barrier model, taking into account the contribution of electrode polarization. It is observed that the Barton-Nakajima-Namikawa relation between the conductivity and the relaxation time is valid for these glasses. The time-temperature superposition principle has been verified using the scaling of the conductivity spectra in the framework of the random barrier model. The charge carrier density, obtained from the Nernst-Einstein relation, is found to be almost independent of temperature, but dependent weakly on composition. We have also studied the influence of the modification of the network structure of these glasses on ion migration and correlated the conductivity with the relative strength of the structural units.

Dynamics and relaxation of charge carriers in poly(methylmethacrylate)-lithium salt based polymer electrolytes plasticized with ethylene carbonate

In this paper, we have studied the dynamics and relaxation of charge carriers in poly(methylmethacrylate)-lithium salt based polymer electrolytes plasticized with ethylene carbonate. Structural and thermal properties have been examined using X-ray diffraction and differential scanning calorimetry, respectively. We have analyzed the complex conductivity spectra by using power law model coupled with the contribution of electrode polarization at low frequencies and high temperatures. The temperature dependence of the ionic conductivity and crossover frequency exhibits Vogel-Tammann-Fulcher type behavior indicating a strong coupling between the ionic and the polymer chain segmental motions. The scaling of the ac conductivity indicates that relaxation dynamics of charge carriers follows a common mechanism for all temperatures and ethylene carbonate concentrations. The analysis of the ac conductivity also shows the existence of a nearly constant loss in these polymer electrolytes at low temperatures and high frequencies. The fraction of free anions and ion pairs in polymer electrolyte have been obtained from the analysis of Fourier transform infrared spectra. It is observed that these quantities influence the behavior of the composition dependence of the ionic conductivity.

High temperature dielectric response in Sm3Fe5O12 ceramics

Abstract Polycrystalline Sm3Fe5O12 ceramics are synthesized by a sol–gel method. High temperature dielectric properties in the frequency range from 100 Hz to 10 MHz are investigated at different temperatures from 300 to 800 K. This material exhibits high dielectric permittivity and low dielectric loss in a wide range of temperature and frequency. The contribution of electrode polarization to the dielectric permittivity is ruled out by the dc bias voltage measurement at room temperature. Two types of dielectric relaxations are clearly observed, and both of them are thermal activated relaxations following the Arrhenius law. The high frequency relaxation is shown to originate from the carrier hopping between Fe2+ and Fe3+, while the low frequency relaxation most likely arises from the conduction. The concentration of Fe2+ is proved to influence the low frequency dielectric relaxation.

Dynamics and relaxation of charge carriers in poly(methylmethacrylate)-based polymer electrolytes embedded with ionic liquid.

In the present paper, we have studied dynamics and relaxation of the charge carriers in polymethylmethacrylate-lithium bis(trifluoromethane sulfonyl)imide polymer electrolytes embedded with 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid. We have analyzed the frequency dependent conductivity spectra using the random free-energy barrier model coupled with the contribution of electrode polarization in the low frequency region. The temperature dependence of ionic conductivity, and relaxation time obtained from the analysis of the spectra exhibits Vogel-Tammann-Fulcher type behavior. The Barton-Nakajima-Namikawa relation is consistent with the results obtained from the random free-energy barrier model. The scaling of ac conductivity spectra has been performed to understand the effect of temperature as well as the composition on the relaxation mechanism. The analysis of the ac conductivity also clearly indicates the existence of a nearly constant loss phenomenon at low temperatures or at high frequencies.

Dielectric relaxations of poly(acrylic acid)-graft-poly(ethylene oxide) aqueous solution: Analysis coupled with scaling approach and hydrogen-bonding complex

Dielectric properties of poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) aqueous solution were measured as a function of concentration and temperature over a frequency range of 40 Hz to 110 MHz. After subtracting the contribution of electrode polarization, three relaxation processes were observed at about 20 kHz, 220 kHz, and 4 MHz, and they are named low-, mid- and high-frequency relaxation, respectively. The relaxation parameters of these three relaxations (dielectric increment Δε and relaxation time τ) showed scaling relations with the polyelectrolyte concentration. The mechanisms of the three relaxations were concluded in light of the scaling theory: The relaxations of low- and mid frequency were attributed to the fluctuation of condensed counterions, while the high-frequency relaxation was ascribed to the fluctuation of free counterions. Based on the dielectric measurements of varying temperatures, the thermodynamic parameters (enthalpy change ΔH and entropy change ΔS) of the three relaxations were calculated and these relaxation processes were also discussed from the microscopic thermodynamical view. In addition, the impacts of PEO side chains on the conformation of PAA-g-PEO chains were discussed. PEO side chains greatly strengthen the hydrogen-bonding interactions between PAA-g-PEO chains, resulting in the chains overlapping at a very low concentration and the formation of a hydrogen-bonding complex. Some physicochemical parameters of PAA-g-PEO molecules were calculated, including the overlap concentration, the effective charge of the chain, the friction coefficient, and the diffusion coefficient of hydrogen counterions.

Increased bandwidth for dielectric spectroscopy of proteins through electrode surface preparation

Dielectric spectroscopy measurements of liquids are often limited by electrode polarization. The influence of surface polishing and deposition of the conducting polymer polypyrrole/polystyrenesulfonate (PPy/PSS) on the polarization impedance is investigated. A quantitative description of the electrode polarization contribution to the real-valued permittivity spectrum is derived. This description explains the origin of the ω(-const). (const.>1) dependency commonly observed in permittivity measurements. Electrode surface roughness is correlated with both the magnitude and phase of the constant phase element. Generally, rougher electrodes have better performance, and an order of magnitude bandwidth improvement is achieved using PPy/PSS electrodes.

Polarization measurements of anode-supported solid oxide fuel cells studied by incorporation of a reference electrode

Abstract A three-electrode system configuration was applied to an anode-supported solid oxide fuel cell where the anode to cathode surface area ratio was ∼7.9, and Ni/YSZ was used as the anode, LSM as the cathode, Pt as the reference electrode, and thin YSZ film as the electrolyte. The cell was polarized potentiostatically at −0.2, −0.4, −0.6 and −0.8 V versus open circuit voltage (OCV) and the potential change versus a reference electrode were recorded to ascertain the relative electrode polarization contributions. The results of these studies suggested that, while the anode contributions to cell polarization were less significant than that observed for the cathode, they were not negligible. Furthermore, the disparity in the relative electrode polarization contribution was observed to decrease with increasing temperature and polarization. Electrode polarization studies suggested that cathodic overvoltage decreased remarkably with increasing temperature whereas anodic overvoltage increased slightly with increasing temperature. Electrode kinetic parameters were extracted from these polarization experiments and the implications of these parameters to cell performance were discussed. Lastly, electrochemical impedance spectroscopy (EIS) data was presented to further elucidate the relative contributions of the anode and cathode impedances on button cell performance.

Electrode Polarization Impedance in Weak NaCl Aqueous Solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.

Low-temperature SOFC with thin film GDC electrolyte prepared in situ by solid-state reaction

Dense electrolyte thin film made of Ce 0.8 Gd 0.2 O 1.90 (GDC20) with a thickness of about 10 μm and supported by Ni-Gd 0.1 Ce 0.9 O 1.95 (GDC) cermet anode was fabricated in situ by solid-state reaction of ceria and gadolinia. The open circuit voltage of this GDC20 cell is 0.86 V at 600 °C and 0.95 V at 500 °C. With La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3 (LSCF)-GDC composite cathode, we could achieve an excellent cell performance with the maximum power density of 578, 358, and 167 mW/cm 2 at 600, 550 and 500 °C, respectively, under open-air conditions. With airflow through the cathode, the maximum power density increases to 625 mW/cm 2 at 600 °C. It was also found that the cell impedance/polarization under open circuit is dominated by electrode polarization contribution; while under high cell overpotential, it is governed by both ohmic loss and electrode polarization contribution.